Self-adaptive driving control method for liquid metal

Abstract

The invention discloses a self-adaptive driving control method for liquid metal. The method comprises the following steps: S1, constructing a microfluid channel structure of the liquid metal; s2, detecting the position of the liquid metal by adopting a plurality of groups of detection assemblies for detecting the position of the liquid metal; s3, performing analog-to-digital conversion on the information detected by the detection assembly by adopting an ADC module to obtain an ADC value; s4, establishing communication between the single-chip microcomputer and the PC terminal through a USART serial port, transmitting the converted ADC value to the PC terminal through the single-chip microcomputer, and storing the converted ADC value as an ADC array through the PC terminal; and S5, the PC terminal processes the ADC array corresponding to the current liquid metal flowing state, calculates the position of the front end of the liquid metal, and performs high-precision driving control on the microfluid pump based on a PID (Proportion Integration Differentiation) algorithm. The motion state of the liquid metal can be fed back in real time, the output speed of the liquid metal is adaptively controlled through data processing, and the control precision is high.

Description

Technical Field

[0001] The present invention relates to the field of liquid metal reconstruction, and in particular to a liquid metal adaptive drive control method. Background Art

[0002] In recent years, liquid metal alloys have been gradually applied to the field of device reconstruction. With the characteristics of liquid form at room temperature, metal alloys can reshape the metal structure of antennas to change the electromagnetic response of devices. Compared with the use of electrical switches or mechanical adjustments, liquid metal reconfiguration can switch between more reconfiguration states.

[0003] Compared with switching devices, liquid metal has the characteristics of continuous tunability and flexible reconstruction; compared with other special materials, it has the advantages of high conductivity, non-toxicity and tastelessness. Therefore, liquid metal has greater advantages in reconfigurable design. However, liquid metal has problems such as easy residue generation when in contact with oxygen, long driving time, and uncontrollable driving, so there are challenges in controlling liquid metal. Among them, the most critical difficulty is to achieve smooth flow of liquid metal in microfluidic channels. Liquid metal is often used in liquid metal electronic devices because of its non-toxicity, high conductivity and low melting point. It can also form a metal oxide layer on the surface under low oxygen concentration conditions. This oxide skin adheres to the surface of most dielectric substrates, leaving tiny droplets or residues of thin conductive coating on the channel wall. Therefore, it is difficult to reversibly and repeatedly circulate the liquid metal in the hollow channel, which hinders the reconfiguration of the device.

[0004] At present, the control scheme for liquid metal reconfiguration mainly adopts two methods: air pressure control and voltage control. In terms of air pressure control, air pumps and syringes are mainly used as air pressure control components to control the movement of liquid metal in the channel by changing the air pressure difference at both ends of the microfluidic channel in the antenna; in terms of voltage control, antenna reconstruction relies on electrochemical methods to control the movement of liquid metal by changing the bias voltage. However, both methods rely on visual feedback from the human eye, and engineers need to manually adjust the reconstruction state. This results in problems such as low reconstruction speed, low liquid metal control accuracy, and more oxide residues. At present, there is no automated drive solution for liquid metal reconstruction.

[0005] In addition, this driving scheme can be applied to multiple liquid metal reconstruction fields, such as the design and implementation of reconfigurable antennas, the manufacture of flexible circuits and sensors, the control and distribution of fluid positions in smart fluid systems, the creation and deformation of conductive connections in wearable technologies, etc. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a liquid metal adaptive drive control method. By establishing a feedback module, the movement state of the liquid metal can be fed back in real time, and the output speed of the liquid metal can be adaptively controlled through data processing, with high control accuracy.

[0007] The object of the present invention is achieved through the following technical solution: A liquid metal adaptive drive control method comprises the following steps:

[0008] S1. Constructing a liquid metal microfluidic channel structure, including:

[0009] A microfluidic channel, one end of which is connected to a liquid storage bottle containing liquid metal through a PTFE tube, and the other end of which is connected to a syringe through a PTFE tube, wherein the syringe is fixed on the microfluidic pump and extracts the liquid metal according to the instructions received by the microfluidic pump;

[0010] S2. Using multiple sets of detection components for detecting the position of liquid metal to detect the position of liquid metal;

[0011] S3. Using the ADC module to perform analog-to-digital conversion on the information detected by the detection component to obtain an ADC value;

[0012] S4. Establish communication between the MCU and the PC through the USART serial port, transmit the converted ADC value from the MCU to the PC, and save it as an ADC array by the PC;

[0013] S5. The PC processes the ADC array corresponding to the current liquid metal flow state, calculates the front end position of the liquid metal, and performs high-precision drive control on the microfluidic pump based on the PID algorithm.

[0014] The beneficial effects of the present invention are as follows: the present invention can provide real-time feedback on the movement state of liquid metal, and adaptively control the output speed of the liquid metal through data processing, thereby achieving high control accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of the architecture adopted by the adaptive drive control method of the present invention;

[0016] Figure 2 It is the PID algorithm execution process;

[0017] Figure 3 Schematic diagram of drive control effect. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0019] A liquid metal adaptive drive control method, the architecture used is as follows Figure 1 As shown, the three-month non-violation period includes the following steps:

[0020] S1. Constructing a liquid metal microfluidic channel structure, including:

[0021] A microfluidic channel, one end of which is connected to a liquid storage bottle containing liquid metal through a PTFE tube, and the other end of which is connected to a syringe through a PTFE tube, wherein the syringe is fixed on the microfluidic pump and extracts the liquid metal according to the instructions received by the microfluidic pump;

[0022] In the embodiment of the present application, in order to avoid oxidation of the liquid metal, mineral oil may be provided on the upper layer of the liquid metal through a layered structure to achieve sealing of the liquid metal;

[0023] In the embodiments of the present application, the forming process of the microfluidic channel is as follows:

[0024] (1) Runner production

[0025] The microfluidic channel integrates the liquid metal flow channel and the PTFE tube fixed short column. In order to achieve higher quality structural production, the microfluidic channel material of this project mainly uses optically transparent resin (Godart8001, GreatSimpleInc). The microfluidic channel model is established using Solidworks, and the microfluidic module is printed using a 3-D printer. The structural accuracy can reach 0.1mm. The transparent resin has a certain strength, and the high light transmittance increases the visibility of the subsequent operation when the liquid metal is injected. Two PTFE tubes are fixed to the fixed short columns at both ends of the microfluidic channel by light-curing glue. One PTFE tube is connected to the liquid storage bottle, and the other is connected to the syringe installed on the microfluidic pump.

[0026] (2) Antioxidant treatment

[0027] Since liquid metal is easily oxidized, it is considered to fill a section of non-oxygen-permeable liquid that is incompatible with it at both ends of EGaIn for sealing. The present invention uses mineral oil as the driving carrier liquid of EGaIn. Mineral oil is a transparent liquid and has a lower radio frequency loss rate than water containing impurities (tanδ<0.01), which is an ideal carrier liquid for anti-oxidation treatment of EGaIn. In order to make EGaIn located between two sections of mineral oil during the injection process, PTFE tube is used as a medium to extract the liquid. The PTFE tube does not need to be moved in the two liquid storage bottles. It only needs to adjust the position of the tube mouth in the liquid to complete the extraction of two different liquids, which also reduces the introduction of oxygen to a certain extent.

[0028] Step 1: Fill the liquid storage bottle with liquid metal and mineral oil. Due to their different densities, stratification will occur (liquid metal is at the bottom and mineral oil is at the top).

[0029] Step 2: Extract liquid so that the liquid metal is sealed in mineral oil. First, place the PTFE tube mouth on the upper layer of PTFE and extract about 2ml of mineral oil. Then, place the PTFE tube on the lower layer and extract the liquid metal. At this time, the liquid metal in the tube is sealed by the first section of mineral oil and the mineral oil on the upper layer of the liquid storage bottle, and is not easy to oxidize.

[0030] (3) Driver architecture:

[0031] One end of the microfluidic channel is connected to a liquid storage bottle containing mineral oil and liquid metal through a PTFE tube, and the other end is connected to a syringe through a PTFE tube. The syringe is fixed on the microfluidic pump and extracts the liquid metal according to the instructions received by the microfluidic pump.

[0032] S2. Using multiple sets of detection components for detecting the position of liquid metal to detect the position of liquid metal;

[0033] In the embodiment of the present application, the single-chip microcomputer and the ADC module adopt the stm32 single-chip microcomputer; since the stm32 single-chip microcomputer has a digital-to-analog conversion channel (ADC), the single-chip microcomputer can realize both the control function of the single-chip microcomputer and the analog-to-digital conversion function;

[0034] Multiple groups of detection components for detecting the position of liquid metal are arranged along the microfluidic channel, and each group of the detection components includes an LED module located above the microfluidic channel and a PD module located below the microfluidic channel; the LED module and the PD module are controlled by a single chip microcomputer;

[0035] The LED module emits a uniform light signal. When the liquid metal flows to the target position, the light signal at the target position will be blocked, and the corresponding PD unit cannot receive the light signal. Each PD module outputs the corresponding voltage data according to the collected light signal.

[0036] In the microfluidic channel, one end of a liquid storage bottle containing liquid metal connected by a PTFE tube is used as the starting point, and the position of each PD module is measured in advance. The position of the PD module refers to: the distance between the projection of the center of the PD module on the microfluidic channel and the initial point, in mm; the PD module uses a photodiode.

[0037] S3. Using the ADC module to perform analog-to-digital conversion on the information detected by the detection component to obtain an ADC value;

[0038] The voltage data is processed by the ADC module in the STM32 and converted into ADC data. The output voltage value will be mapped into an integer value between 0 and 4095 through the digital-to-analog conversion channel of the STM32.

[0039] In each group of detection components, the voltage data output by the PD module is converted into ADC data after passing through the ADC module: specifically, the output voltage value is mapped into an integer value in a preset area through the conversion channel of the ADC module. The mapped ADC value is shown in formula (1):

[0040] ADC value = (input voltage / reference voltage) * ADC resolution (1)

[0041] The voltage data output by each PD module needs to be converted into an ADC value using an ADC module. The number of conversion channels of the ADC module needs to be greater than or equal to the number of PD modules, so that the voltage data output by each PD module has a conversion channel to complete the mapping of the above ADC value;

[0042] S4. Establish communication between the MCU and the PC through the USART serial port, transmit the converted ADC value from the MCU to the PC, and form an ADC array;

[0043] Establish communication between the MCU and the PC through the USART serial port, and transmit the converted ADC value from the MCU to the PC;

[0044] The ADC module sends an ADC value every 0.5s. The ADC value of each transmission is set to a four-digit number in the single-chip microcomputer, that is, the data transmitted by the single chip each time is sent in a four-digit format. If the ADC value is less than four digits, 0 is added in front of the ADC value.

[0045] In the MATLAB program on the PC, four ASCII codes are read each time and converted into ADC values ​​for storage;

[0046] Since there are multiple PD modules, the ADC values ​​corresponding to each PD module need to be sent to the PC, which saves them as an ADC array and records the PD module corresponding to each ADC value in the ADC array.

[0047] S5. The PC processes the ADC array corresponding to the current liquid metal flow state in MATLAB, calculates the front end position of the liquid metal, and performs high-precision drive control on the microfluidic pump based on the PID algorithm.

[0048] The PC processes the ADC array corresponding to the current liquid metal flow state and calculates the front end position of the liquid metal, including:

[0049] First, two thresholds are set in MATLAB on the PC, denoted as ADC1 and ADC2, where ADC1 is less than ADC2;

[0050] It is defined that when the ADC value is less than ADC1, the corresponding PD unit is completely blocked by the liquid metal, and when the ADC value is greater than ADC2, the corresponding PD module is not blocked by the liquid metal; it is defined that when the ADC value is greater than or equal to ADC1, and less than or equal to ADC2, the corresponding PD module is partially blocked by the liquid metal, and the end of the current liquid metal is located within the projection of the PD module in the microfluidic channel;

[0051] When completely blocked, the light received by the PD module is mainly ambient light, so the ADC value is low, so ADC1 is generally set to 50; when not blocked, the PD module can receive relatively complete LED light, so the ADC value is high, so ADC2 is generally set to 2000; and partially blocked is between the two, so as long as the ADC value is greater than or equal to ADC1 and less than or equal to ADC2, the partially blocked PD module can be determined;

[0052] From the ADC values ​​in the ADC array, select the value that is greater than or equal to ADC1 and less than or equal to ADC2, and record it as ADC n , and the corresponding PD module position is recorded as PD n ;

[0053] In MATLAB on the PC, the ADC array corresponding to the current liquid metal flow state is processed to calculate the front position of the liquid metal. The calculation formula is shown in formula (2). This formula is fitted by the experimental results of liquid metal in a flow channel with a width of 2 mm and a height of 0.5 mm. This formula needs to be adjusted according to the different reconstructed antenna structures.

[0054] Current liquid metal position = PD n +0.0005*ADC n *ADC n -0.03*ADC n +0.23(2)

[0055] EGaIn liquid metal is very likely to produce an oxide layer after contacting oxygen, leaving residues in the flow channel. This phenomenon is difficult to avoid in actual experiments, so the operating state of the liquid metal each time has a certain degree of operating difference. When the target distance is the same, EGaIn cannot run the same distance when the same operating requirements are set for the microfluidic pump. The oxidizability of liquid metal and the hysteresis effect during flow require precise control of the drive of liquid metal in practical applications. According to the current liquid metal fitting position, the PID algorithm is used to control the movement of the microfluidic pump until the position information is detected to meet the preset requirements. The PID execution process is as follows Figure 2 shown.

[0056] First, specify the target position of the liquid metal in MATLAB, and the system Figure 2 Iterate. In the kth iteration, PD first monitors the flow state of the liquid metal, and the data is transmitted to STM32 in the form of voltage, and further transmitted to MATALB in the form of ADC array. In MATLAB, the current position of the front end of the liquid metal can be calculated by (2). The difference between the target position of the liquid metal and the current running position of the liquid metal is used as the input of the PID algorithm. After proportional, integral, and differential operations, the output speed of the liquid metal drive pump in the current state can be obtained. The specific relationship is shown in formula (3):

[0057] u(k)=K p (err(k)+K i ∑err(k)+K d (err(k)-err(k-1))) (3)

[0058] Wherein, u(k) is the operating speed of the microfluidic pump after the kth iteration, and err(k) is the difference between the target position of the liquid metal and the current operating position of the liquid metal. p , K i , K d Represent the control parameters of proportional, integral and differential operations respectively. After calculating the current running speed u(k), the output speed is sent to the pump in the form of ASCII code to control the running speed of the pump. After the pump runs for 0.5s, PD reads the running status of the liquid metal again and performs the k+1th round of iteration. This process is iterated cyclically with a time interval of 0.5s until the error condition is met. The specific PID parameters need to be adjusted according to the running status. Under the conditions of a flow channel width of 2mm and a height of 0.5mm, the PID control parameters are as follows: K p =8,K i =0.01,K d = 1. Ultimately, high-precision automatic control of liquid metal can be achieved, and the design of high-precision driving methods also makes continuous reconstruction of liquid metal possible.

[0059] In the embodiments of the present application, the control effect is as follows Figure 3 As shown. After the liquid metal moves to the target position, it continues to move forward a certain distance due to the hysteresis effect. Under the action of the PID algorithm, the pump changes from the extraction state to the injection state, and switches between the two states according to the position of the liquid metal, so that the front end of the liquid metal finally reaches the specified position. It can be seen from the experimental results that the control accuracy of the liquid metal in the present invention can reach ±0.5mm.

[0060] The above is a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not depart from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A liquid metal adaptive drive control method, characterized in that: The following steps are involved: S1. Constructing a liquid metal microfluidic channel structure, including: A microfluidic channel, one end of which is connected to a liquid storage bottle containing liquid metal through a PTFE tube, and the other end of which is connected to a syringe through a PTFE tube, wherein the syringe is fixed on a microfluidic pump and extracts liquid metal according to instructions received by the microfluidic pump; S2. Using multiple sets of detection components for detecting the position of liquid metal to detect the position of liquid metal; S3. Using the ADC module to perform analog-to-digital conversion on the information detected by the detection component to obtain an ADC value; S4. Establish communication between the MCU and the PC through the USART serial port, transmit the converted ADC value from the MCU to the PC, and save it as an ADC array by the PC; S5. The PC processes the ADC array corresponding to the current liquid metal flow state, calculates the front end position of the liquid metal, and performs high-precision drive control on the microfluidic pump based on the PID algorithm.

2. A liquid metal adaptive driving control method according to claim 1, characterized in that: The microfluidic channel is a transparent channel.

3. The liquid metal adaptive driving control method according to claim 1, characterized in that: In step S2, multiple groups of detection components for detecting the position of liquid metal are arranged along the microfluidic channel, and each group of the detection components includes an LED module located above the microfluidic channel and a PD module located below the microfluidic channel; the LED module and the PD module are controlled by a single chip microcomputer; The LED module emits a uniform light signal. When the liquid metal flows to the target position, the light signal at the target position will be blocked, and the corresponding PD unit cannot receive the light signal. Each PD module outputs the corresponding voltage data according to the collected light signal. In the microfluidic channel, one end of a liquid storage bottle containing liquid metal connected by a PTFE tube is used as the starting point, and the position of each PD module is measured in advance. The position of the PD module refers to the distance between the projection of the center of the PD module on the microfluidic channel and the initial point.

4. The liquid metal adaptive driving control method according to claim 1, characterized in that: In step S3, in each group of detection components, the voltage data output by the PD module is converted into ADC data after passing through the ADC module: specifically, the output voltage value is mapped into an integer value of a preset area through the conversion channel of the ADC module, and the mapped ADC value is shown in formula (1): ADC value = (input voltage / reference voltage) * ADC resolution (1) The voltage data output by each PD module will need to be converted into an ADC value using an ADC module. The number of conversion channels of the ADC module needs to be greater than or equal to the number of PD modules so that the voltage data output by each PD module has a conversion channel to complete the mapping of the above ADC value.

5. The liquid metal adaptive driving control method according to claim 1, characterized in that: In step S4, communication between the single-chip microcomputer and the PC is established through the USART serial port, and the converted ADC value is transmitted from the single-chip microcomputer to the PC; The ADC module sends an ADC value every 0.5s. The ADC value of each transmission is set to a four-digit number in the microcontroller, that is, the data transmitted by the chip each time is sent in a four-digit number. If the ADC value is less than four digits, 0 is added in front of the ADC value. In the MATLAB program on the PC, four ASCII codes are read each time and converted into ADC values ​​for storage; Since there are multiple PD modules, the ADC values ​​corresponding to each PD module need to be sent to the PC, which saves them as an ADC array and records the PD module corresponding to each ADC value in the ADC array.

6. The liquid metal adaptive driving control method according to claim 1, characterized in that: In step S5, the PC processes the ADC array corresponding to the current liquid metal flow state to calculate the front end position of the liquid metal, including: First, two thresholds are set in MATLAB on the PC, denoted as ADC1 and ADC2, where ADC1 is less than ADC2; It is defined that when the ADC value is less than ADC1, the corresponding PD unit is completely blocked by the liquid metal, and when the ADC value is greater than ADC2, the corresponding PD module is not blocked by the liquid metal; it is defined that when the ADC value is greater than or equal to ADC1, and less than or equal to ADC2, the corresponding PD module is partially blocked by the liquid metal, and the end of the current liquid metal is located within the projection of the PD module in the microfluidic channel; From the ADC values ​​in the ADC array, select the value that is greater than or equal to ADC1 and less than or equal to ADC2, and record it as ADC n , and the corresponding PD module position is recorded as PD n ; Calculate the current liquid metal position, the calculation formula is shown in formula (2): Current liquid metal position = PD n +a* ADC n * ADC n -b* ADC n +c; (2) Among them, a, b, and c are fitting coefficients.

7. The liquid metal adaptive driving control method according to claim 1, characterized in that: The step S5 comprises: Specify the target position of the liquid metal in MATLAB on the PC, and then perform precise control through iteration: In the kth iteration, the PD first monitors the flow state of the liquid metal, and the data is transmitted to the ADC module in the form of voltage for analog-to-digital conversion. The microcontroller receives the conversion result and transmits it to the PC. In MATLAB on the PC, the current position of the front end of the liquid metal is calculated by (2); The difference between the target position of the liquid metal and the current running position of the liquid metal is used as the input of the PID algorithm. After proportional, integral and differential operations, the output speed of the liquid metal driving pump in the current state is obtained. The specific relationship is shown in formula (3): u(k)=K p (err(k)+K i ∑err(k)+K d (err(k)-err(k-1))) (3) Wherein, u(k) is the running speed of the microfluidic pump after the kth iteration, err(k) is the difference between the target position of the liquid metal and the current running position of the liquid metal, and K p , K i , K d They represent the control parameters of proportional, integral and differential operations respectively; when u(k) is positive, the microfluidic pump performs extraction action, and the liquid storage bottle transports liquid metal to the channel; when u(k) is 0, the microfluidic pump has no action; when u(k) is negative, the microfluidic pump performs retraction action, and the metal in the channel flows back to the liquid storage bottle; After calculating the current round running speed u(k), the output speed is sent to the pump in the form of ASCII code to control the running speed of the pump; after the pump runs for ts, PD reads the running status of the liquid metal again and performs the k+1th round of iteration. Steps S2 to S4 are repeated in each iteration process; Each iteration uses ts as the time interval until the error condition is met. The error condition means that the error between the target position and the liquid metal position is less than the set threshold. The error condition is met for m consecutive times, and the speed u(k) is set to 0 until the target position changes, and then steps S2 to S4 are repeated.

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