CN117269323B - Micro-resonance type mass sensor for magnetic suspended matters in liquid and detection method - Google Patents
Micro-resonance type mass sensor for magnetic suspended matters in liquid and detection method Download PDFInfo
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Abstract
The invention relates to a magnetic suspended matter micro-resonance type mass sensor in liquid and a detection method thereof, comprising the following steps: the device comprises a circuit board, a control unit, an energy supply unit, a receiving unit, a voltage control unit, a digital-analog conversion unit, an output unit and a detection unit, wherein the detection unit comprises an R-shaped orthogonal micro-cantilever, a piezoelectric driving mechanism, a vibration pickup mechanism, a magnetic adsorption layer and an insulating film, the piezoelectric driving mechanism is used for driving the micro-cantilever to vibrate through power supply of an operational amplifier, the vibration pickup mechanism is used for converting vibration signals into voltage signals and transmitting the voltage signals to the receiving unit, the insulating film is used for preventing the magnetic adsorption layer from adsorbing sundries to cause detection errors before use, and the magnetic adsorption layer is used for adsorbing magnetic suspended matters in liquid; the invention has the advantages that: the rear end of the cantilever girder is immersed in the liquid to sense the mass of the magnetic suspended matters in the liquid, and meanwhile, the inner resonance information of the rear end of the girder, the tail end of which is immersed in the liquid, and the auxiliary girder exposed in the air is collected to detect, so that the separation of sensing and detection is realized.
Description
Technical Field
The invention belongs to the technical field of micro-mass sensing, and relates to a STM 32-based control micro-resonance type liquid magnetic suspended matter mass sensor and a detection method.
Background
Magnetic suspensions are impurities in the oil that, when present in the oil, may lead to a reduction in the quality of the oil. These suspensions may include metal particles, iron powder, rust, and the like. They may cause wear on mechanical equipment, reduce equipment life, and reduce oil performance. The presence of the magnetic suspension may alter the fluid properties of the oil. They may cause an increase in viscosity, making the oil more viscous, which may affect the flow properties of the fluid in the lubrication system. The presence of magnetic suspensions may alter the thermal and insulating properties of the oil. This can have negative effects on certain industrial applications and systems where lubrication requirements are very high. In industrial production, it is critical to ensure that no additional impurities are present in the product. By measuring the amount of magnetic suspended matter in the liquid, the quality on the production line can be monitored and controlled, and the product is ensured to meet the specification. In mining and mineral processing, measuring the amount of magnetic suspension aids in the separation and extraction of useful minerals or ores. Therefore, researchers have been eager to develop and research liquid magnetic suspended matter mass sensors. The micro-resonant sensor is a multifunctional, high-sensitivity, miniaturized and low-power-consumption sensing technology and is widely applied to various fields.
In most conventional micro-resonant sensors, a single cantilever beam is used as a core detection element, the single cantilever beam is completely immersed in a liquid, and a piezoelectric sheet is used to collect a voltage signal containing vibration information. However, in the experimental process, the single cantilever beam immersed in the liquid is affected by the large damping liquid, the quality factor of the output signal is very low, the subsequent signal processing and the liquid magnetic suspended matter mass resolving are not facilitated, and the traditional micro-resonance sensor mainly relies on the linear vibration information of the single cantilever beam to detect the magnetic suspended matter mass, so that the resonance frequency deviation of the cantilever beam in the liquid in the linear vibration state is small, and the detection sensitivity is very low.
Disclosure of Invention
In view of the above problems, the present invention is directed to a micro-resonant type mass sensor and a detection method for magnetic suspended substances in a liquid, which are used for solving the disadvantages of low detection sensitivity and low quality factor of output signals of the conventional micro-resonant type sensor. The liquid magnetic suspension quality detection device can detect the liquid magnetic suspension quality, has the advantages of miniaturization and intellectualization, and can greatly improve the detection sensitivity and the quality factor of output signals.
The invention provides a magnetic suspension micro-resonance type mass sensor in liquid, which comprises: the device comprises a circuit board, a control unit, an energy supply unit, a receiving unit, a voltage control unit, a digital-to-analog conversion unit, an output unit and a detection unit, wherein the control unit is arranged on the circuit board through leads and pins, the control unit comprises an STM32 control chip and a crystal oscillator, the energy supply unit is used for supplying power to the circuit board, the receiving unit is used for transmitting detection signals of the detection unit to the STM32 control chip, the voltage control unit is used for changing the voltage to reach rated voltage of the circuit board and components, the digital-to-analog conversion unit is used for converting digital signals of the STM32 control chip into analog signals to be transmitted to an operational amplifier so as to excite the detection unit, the output unit is used for outputting signals, and the detection unit is used for collecting vibration signals in a liquid, and the improvement is that the detection unit comprises an R-shaped orthogonal micro-cantilever beam, a piezoelectric driving mechanism arranged on the R-shaped orthogonal micro-cantilever beam, a vibration pickup mechanism, a magnetic adsorption layer and an insulating film tightly attached to the magnetic adsorption layer, wherein the piezoelectric driving mechanism drives the R-shaped orthogonal micro-cantilever beam to vibrate through an operational amplifier, the vibration pickup mechanism is used for converting the signals into analog signals to be used for blocking the voltage signals to be transmitted to the receiving signals to an operational amplifier, and the analog signals, and the output signals are used for absorbing magnetic signals and the magnetic signals are used for absorbing magnetic impurities and the magnetic signals;
wherein, the orthogonal micro-cantilever of R shape includes: the device comprises an upper main beam, a lower main beam and an auxiliary beam, wherein the upper main beam and the lower main beam are rectangular plate-shaped, the auxiliary beam is arranged on one side of the main beam and is integrally formed with the upper main beam, the upper main beam is fixedly connected with the lower main beam and is vertically arranged, a piezoelectric driving mechanism and a vibration pickup mechanism are arranged at the upper end of the upper main beam, the vibration pickup mechanism is arranged at a position, close to the upper main beam, on the auxiliary beam, a magnetic adsorption layer and an insulating film tightly attached to the magnetic adsorption layer are adhered to the lower main beam, and the piezoelectric driving mechanism and the vibration pickup mechanism comprise: a positive electrode plate connected with the positive electrode, a negative electrode plate connected with the negative electrode, and piezoelectric materials positioned below the positive electrode plate and the negative electrode plate; the piezoelectric material is a crystal material that generates a voltage between both end surfaces when subjected to pressure. The piezoelectric effect is to generate weak current when the piezoelectric material is deformed by external force. The upper main beam and the lower main beam are arranged at 90 degrees, so that liquid resistance borne by the R-shaped orthogonal micro-cantilever beam during detection in liquid is reduced, when the R-shaped orthogonal micro-cantilever beam is vertically inserted into the liquid and vibrated by a bending mode, the phenomenon that boundary layer separation phenomenon occurs at the tail end of the cantilever beam when a blunt body is regarded as in the liquid, so that turbulence is generated by liquid at the tail end of the cantilever beam to generate pressure difference to form extremely large differential pressure resistance, vibration of the micro-cantilever beam is hindered, good micro-cantilever beam vibration signals are difficult to collect, larger error is caused for detection, in order to reduce the differential pressure resistance of the liquid, the rear end of the R-shaped orthogonal micro-cantilever beam is rotated for 90 degrees in the vertical direction, at the moment, the upper main beam and the lower main beam are in an orthogonal relation in space, the rear end of the main beam moves in the liquid to perform shearing vibration, at the moment, the contact area with the liquid is greatly reduced, the streamline body is regarded as in the liquid, boundary layer separation phenomenon does not occur at the tail end of the beam, the turbulent flow is not generated at the tail end of the beam, the differential pressure resistance is not generated, the detection error caused by the differential pressure resistance is eliminated, and quality factor of detection is greatly improved.
The piezoelectric driving mechanism and the vibration picking mechanism on the upper main beam share a negative electrode plate, and the electrode plates of the piezoelectric driving mechanism and the vibration picking mechanism on the upper main beam are arranged at the edge of the upper end of the main beam and are arranged at two sides of the negative electrode plate in parallel;
the positive electrode plate and the negative electrode plate of the vibration pickup mechanism positioned on the auxiliary beam are arranged on the auxiliary beam at a position close to the upper main beam;
the positive electrode plate and the negative electrode plate of the piezoelectric driving mechanism drive the upper girder, the lower girder and the auxiliary girder to vibrate through the power supply of the operational amplifier, the positive electrode plate and the negative electrode plate of the vibration pickup mechanism on the upper girder and the auxiliary girder convert vibration signals into voltage signals and transmit the voltage signals to ADC pins of the receiving unit, and the receiving unit transmits the voltage signals to the STM32 control chip for signal identification.
As the optimization of the invention, by adding the auxiliary beam on the upper main beam, when the piezoelectric driving mechanism applies the frequency corresponding to the first-order mode to the R-shaped orthogonal micro-cantilever beam, the upper main beam vibrates greatly; when the piezoelectric driving mechanism applies a frequency corresponding to a second-order mode to the R-shaped orthogonal micro-cantilever, the auxiliary beam vibrates greatly; the first-order mode and the second-order mode refer to vibration frequencies set by the sensor, vibration of the piezoelectric driving mechanism is decomposed and coupled into a plurality of (N) orthogonal single-degree-of-freedom vibrations, the plurality of (N) modes of the sensor are corresponding, each mode has a natural frequency, and the frequency ratio of the first-order mode to the second-order mode is set to be 1:2, exciting the R-shaped orthogonal micro-cantilever beam by the piezoelectric driving mechanism at a frequency corresponding to a first-order mode, outputting a piezoelectric signal (vibration information) of the auxiliary beam through the vibration pickup mechanism, and obtaining a first harmonic wave and a second harmonic wave after Fourier transformation is carried out on the piezoelectric signal of the auxiliary beam, wherein the frequencies corresponding to the first-order mode and the second harmonic wave correspond to frequency values corresponding to the first-order mode and the second-order mode respectively; when the R-shaped orthogonal micro-cantilever beam is applied with mass, repeating the above operation to obtain new frequency values corresponding to the first harmonic and the second harmonic, wherein the frequency offset corresponding to the first harmonic and the frequency offset corresponding to the second harmonic obtained in the front and the back is 1:2, thereby forming a frequency multiplication mechanism, regulating and controlling the frequency ratio of the frequency offset of the first harmonic and the second harmonic by controlling the frequency ratio of the first-order mode and the second-order mode, and realizing the improvement of sensitivity by the frequency multiplication mechanism.
As the preferable mode of the invention, the control chip converts the digital signal into the analog signal through the digital-analog conversion unit and transmits the analog signal to the operational amplifier, controls the operational amplifier to excite the detection unit, and the detection unit transmits the detection signal to the receiving unit and then back to the STM32 control chip through the receiving unit, and the detection signal is transmitted to the output unit for signal output after being processed by the processing module of the STM32 control chip; the control unit crystal oscillator is used for providing a basic clock signal and mainly controlling the STM32 control chip, the processing module is used for calculating to obtain additional mass and additional damping digital signals, the digital signals are transmitted to the CAN interface chip, and finally the CAN interface chip is transmitted to the external display to display the obtained additional mass and additional damping specific values.
As a preferred aspect of the present invention, the power supply unit includes an external power supply and an operational discharge source chip inside the circuit board; the external power supply is used for supplying power to the PCB circuit board to enable the PCB circuit board to work normally; the operational amplifier is connected with the operational amplifier through the operational amplifier source chip.
As a preferred aspect of the present invention, the receiving unit includes a power pin, an output pin, and an ADC pin; the ADC pin header is used for transmitting detection signals of the detection unit to the STM32 control chip, the power pin header is used for connecting a power end, and the output pin header is used for being connected with the output unit.
As a preferred aspect of the present invention, the voltage control unit includes a schottky diode, an inductor, a capacitor, a resistor, a voltage stabilizer, a buck chip, and a boost chip; the Schottky diode is used for freewheeling and stabilizing voltage to enable the circuit to work normally; the inductor is used for storing energy and filtering so that the circuit works normally; the capacitor is used for filtering and stabilizing voltage to enable the circuit to work normally; the resistor is used for stabilizing current and dividing voltage to enable the circuit to work normally; the voltage stabilizer is used for stabilizing voltage to enable the circuit to work normally; the voltage reduction chip reduces the standard 5V voltage of an external computer to 3.3V to reach the normal working standard voltage of the circuit element; the boosting chip comprises an operational amplifier and an operational amplifier; the operation and discharge source chip increases the standard 5V voltage of an external computer to 12V and supplies power to the operational amplifier; the operational amplifier increases the 3.3V working standard voltage in the PCB to 10V and supplies power to the piezoelectric driving mechanism in the detection unit so as to detect vibration.
Preferably, the digital-to-analog conversion unit comprises a digital-to-analog conversion chip, and the digital-to-analog conversion chip is used for converting a digital signal of the STM32 control chip into an analog signal and transmitting the analog signal to the operational amplifier so as to excite the detection unit.
As the preferable choice of the invention, the said output unit includes CAN interface chip and external display pin header; and the CAN interface chip transmits the digital signals processed by the STM32 control chip to the external display through the external display pin header to output the digital signals.
Another object of the present invention is to provide a method for detecting a magnetic suspended matter micro-resonant mass sensor in a liquid, comprising the steps of:
step one: fixing a magnetic suspended matter micro-resonance type mass sensor controlled by an STM32 control chip on a three-dimensional moving platform, adjusting the three-dimensional moving platform to enable the direction of a detection unit to be downward and to be in a vertical relation with the horizontal plane of an experiment table, and then fixing the x direction and the y direction of the three-dimensional moving platform, wherein the three-dimensional moving platform can only move in the vertical direction of a z axis;
step two: placing the liquid to be detected into a beaker, and adjusting a three-dimensional moving platform to submerge the front end beam of the detection unit into the liquid to be detected;
step three: connecting the magnetic suspended matter micro-resonance type quality sensor with a power pin on a PCB (printed circuit board) and an external computer through a data line, and supplying power by using an external power supply;
step four: the PCB is electrified to work normally, the STM32 control chip controls the operational amplifier to input excitation voltage sweep frequency signals to the piezoelectric driving mechanism through the processing module, and the detection unit is driven to vibrate integrally;
step five: voltage values of main beam and auxiliary beam during internal resonance reading through ADC pin headerAnd the phase of the main beam and the auxiliary beam is obtained by carrying out Fourier transform processing through a control chip>According to the formula->Converting the voltage value to an amplitude +.>，/>For the electromechanical coupling coefficient of the piezoelectric material, +.>Parasitic capacitance of piezoelectric material, +.>For the output voltage of the piezo-electric sheet, < >>For the output ac voltage of the piezo-electric sheet, +.>Is a resistor in the circuit;
step six: additional mass to liquid using liquid mass sensing equationAdditional damping->Performing solution;
step seven: the solution equation for the liquid mass sensing equation is derived as follows:
firstly, after immersing an R-shaped orthogonal micro-cantilever into liquid, establishing a motion equation to obtain:
formula 1;
formula 2;
then solving for the additional mass using a multiscale methodAdditional damping->：
Introducing small disturbance parameters=0.001，
Order the；
；
；
；
；
；
The approximate solution of the final periodic solution can be expressed as:
formula 3;
formula 4;
the external excitation is in the form ofcoswt，Therefore, it is- 、 />The phase difference of the responses of the low-frequency sensing beam and the high-frequency detecting beam is respectively calculated by +.>And->Indicating (I)>And->，/>And->Are equal in value to each other in terms of the number,/>、/>the phase parameter is used for representing the response phase difference of the cantilever beam;
wherein the method comprises the steps ofIs equivalent to the main beam in mass->Is equivalent mass of the auxiliary beam->Is the inherent damping of the main beam->Is the inherent damping of the secondary beam->For the vibration response of the main beam, +.>For the vibrational response of the secondary beam +.>Is the vibration amplitude of the main beam>For the vibration amplitude of the auxiliary beam +.>For the phase of the vibration of the main beam->For the phase of the vibration of the secondary beam +.>For the linear rigidity of the main beam->For the linear stiffness of the secondary beam +.>Is nonlinear rigidity>And->For the excitation frequency, is a coordinated quantity,for externally excited acceleration->Additional mass applied to the girder for the liquid, < >>Additional damping applied to the main beam for the liquid; />Is the vibration speed of the main beam, +.>The vibration speed of the auxiliary beam; />Is the vibration acceleration of the main beam, +.>The vibration acceleration of the auxiliary beam; w is the driving frequency applied to the cantilever, < >>For the response frequency of the main beam, < > is>The response frequency of the secondary beam; />Infinitesimal>Infinitesimal>Is infinitely small, t is time, +.>Is nonlinear stiffness;
formula 6;
6 type；
7 type；
8 type；
Wherein,is the vibration amplitude of the main beam>The vibration amplitude of the auxiliary beam is set; />And->Is the theoretical excitation frequency and is the coordination quantity;for the response frequency of the main beam, < > is>Response frequency of secondary beam, +.>Is nonlinear stiffness; />For externally excited acceleration->、The phase parameter is used for representing the response phase difference of the cantilever beam;
，（j，k=1,2）
from equation 5 over equation 6:
9 type；
Similarly, the formula 7 is compared with the formula 8:
formula 10;
combining 7 and 8 to calculate the additional massAdditional damping->：
Formula 11;
formula 12;
due to the additional massAdditional damping->Except for the phase of the main beam and the auxiliary beam>、/>Through experiments on the displacement a and the displacement b of the main beam and the auxiliary beamThe other parameters are constant except for the acquisition, so that when the external environment is not changed, the additional mass is known by experiments before the mass disturbance is not applied>Additional damping->And is a fixed value;
removing the insulating film on the magnetic adsorption layer, and allowing the detection unit to start adsorbing magnetic suspended substances in the liquidThe equation of motion at this time can be listed as:
；
；
the mass equation of the magnetic suspended matters can be obtained by using a multi-scale method:
formula 13;
formula 14;
neglecting the change in mass after application of the magnetic substance, it can be seen from the above that the mass is addedAdditional damping->For the fixed value, the nine and ten formulas are combined to know the quantity of the magnetic suspended substances>：
15 type；
Wherein the method comprises the steps of，/>Is prepared from magnetic substance>Frequency of change, ++>Is prepared from magnetic substance>Varying phase.
The invention has the advantages and positive effects that:
1. the invention perceives the magnetic suspended matter mass in the liquid by immersing the rear end of the main beam of the R-shaped orthogonal micro-cantilever in the liquid, and simultaneously collects the internal resonance information of the rear end of the main beam with the tail immersed in the liquid and the auxiliary beam exposed in the air for detection, thereby realizing the separation of sensing and detection.
2. According to the method, the R-shaped orthogonal cantilever girder is subjected to rotary treatment at two thirds, so that the upper girder and the lower girder are formed, the upper girder and the lower girder form an orthogonal relationship in space, at the moment, the lower girder moves in liquid to perform shearing vibration, the contact area of the lower girder and the liquid is greatly reduced, the lower girder is regarded as a streamline body in the liquid, the boundary layer separation phenomenon cannot occur on the lower girder, the turbulent flow cannot be generated on the lower girder of the liquid, and the differential pressure resistance cannot be generated, so that the detection error caused by the differential pressure resistance is eliminated, and the quality factor of detection is greatly improved.
3. According to the method, the liquid magnetic substance quality is detected through the internal resonance effect generated on the R-shaped orthogonal micro-cantilever beam, the frequency multiplication characteristic of the internal resonance effect is utilized, after the frequency deviation of an output signal on the auxiliary beam is an integral multiple of the main beam, and therefore, compared with a traditional micro-resonance type sensor, the sensitivity of the liquid magnetic suspension quality detection is improved by a plurality of times.
4. The application realizes the microminiaturization and the intelligent sensing scheme by carrying the STM32 control chip and controlling and driving the detection unit through the PCB.
Drawings
FIG. 1 is a schematic diagram of the structure of the present invention;
FIG. 2 is a front view of the structure of FIG. 1 in accordance with the present invention;
FIG. 3 is a side view of the structure of FIG. 1 in accordance with the present invention;
FIG. 4 is a top view of the structure of FIG. 1 in accordance with the present invention;
FIG. 5 is an enlarged view of a detail of the detection unit in the structure of FIG. 1 according to the present invention;
FIG. 6 is a front view of the structure of FIG. 5 in accordance with the present invention;
FIG. 7 is a side view of the structure of FIG. 5 in accordance with the present invention;
FIG. 8 is a top view of the structure of FIG. 5 in accordance with the present invention;
FIG. 9 is a circuit control flow diagram of the present invention;
FIG. 10 is a graph showing the comparison of the quality factors of vibration signals in air and liquid according to the present invention;
FIG. 11 is a graph showing the comparison of the quality factors of vibration signals in air and liquid of a conventional micro-resonant sensor.
Reference numerals: capacitor 1, crystal oscillator 2, step-down chip 3, CAN interface chip 4, external display pin 5, power pin 6, detection unit 7, upper main beam 7a, lower main beam 7b, magnetic adsorption layer and insulating film 7c, positive electrode plate 7d, auxiliary beam 7e, negative electrode plate 7f, positive electrode plate 7g, negative electrode plate 7 h', positive electrode plate 7i, output pin 8, resistor 9, operational amplifier 10, control chip 11, digital-analog conversion chip 12, ADC pin 13, crystal oscillator 14, operational source chip 15, schottky diode 16, voltage stabilizer 17, inductor 18.
Detailed Description
In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident, however, that such embodiment(s) may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing one or more embodiments.
Example 1
Referring to fig. 1-11, the present embodiment provides a micro-resonant liquid magnetic suspended matter mass sensor based on STM32 control: the device comprises a control unit, an energy supply unit, a receiving unit, a voltage control unit, a digital-analog conversion unit, an output unit and a detection unit; all units are connected to a PCB circuit board in a lead and pin welding mode; the control unit comprises an STM32 control chip 11, crystal oscillators 2 and 14; the energy supply unit comprises an external power supply and a circuit board internal power supply chip; the receiving unit comprises a power supply pin 6, an output pin 8 and an ADC pin 13; the voltage control unit is used for changing the voltage to reach the rated voltage of the circuit board and the components; the digital-to-analog conversion unit is used for converting the digital signal of the STM32 control chip into an analog signal and transmitting the analog signal to the operational amplifier so as to excite the detection unit; the output unit is used for outputting signals; the detection unit 7 is welded on the whole PCB through the lead wires and the electrodes of the output pin 8.
As shown in fig. 5, the R-shaped orthogonal micro-cantilever in this embodiment includes: an upper girder 7a and a lower girder 7b which are rectangular plate-shaped, a secondary girder 7e which is arranged on one side of the girder 7a and is integrally formed with the upper girder 7a, a positive electrode plate 7g, a negative electrode plate 7h 'of a piezoelectric driving mechanism, a negative electrode plate 7 h' of a vibration pickup mechanism, a positive electrode plate 7i, a negative electrode plate 7f, a positive electrode plate 7d, a magnetic adsorption layer and an insulating film 7c, a positive electrode plate 7g, a negative electrode plate 7h 'of the piezoelectric driving mechanism, a negative electrode plate 7 h' of the vibration pickup mechanism, a positive electrode plate 7i, a negative electrode plate 7f, a positive electrode plate 7d, an R-shaped orthogonal cantilever beam upper girder 7a, a lower girder 7b and a secondary girder 7e, wherein the insulating film is tightly attached to the magnetic adsorption layer 7c, the magnetic adsorption layer 7c is adhered to the lower girder 7b, two thirds of the electrode plates are separated into the upper girder 7a and the lower girder 7b, the lower girder 7a is fixedly connected with the positive electrode plate 7g, the negative electrode plate 7h 'of the piezoelectric driving mechanism and the positive electrode plate 7 h' is fixedly connected with the vibration pickup mechanism and the lower girder 7 i; the piezoelectric material is a crystal material that generates a voltage between both end surfaces when subjected to pressure. The piezoelectric effect is to generate weak current when the piezoelectric material is deformed by external force. The negative electrode plate 7h 'of the piezoelectric driving mechanism and the negative electrode plate 7 h' of the vibration pickup mechanism share the same negative electrode, namely the negative electrode plate 7h 'and the negative electrode plate 7 h' belong to the same negative electrode plate, and the negative electrode plate belongs to the piezoelectric driving mechanism and the vibration pickup mechanism. The positive electrode plate 7g and the negative electrode plate 7h 'of the piezoelectric driving mechanism drive the micro-cantilever beam to vibrate through the power supply of the operational amplifier, and the negative electrode plate 7 h' and the positive electrode plate 7i of the vibration pickup mechanism convert vibration signals into voltage signals and transmit the voltage signals to the ADC row pins 13; the lower main beam 7b is 90 degrees with the upper main beam 7a in the vertical direction, so as to reduce the liquid resistance born by the micro-cantilever system when the micro-cantilever system is detected in liquid, when the cantilever beam is vertically inserted into the liquid and vibrated by a bending mode, the boundary layer separation phenomenon can occur at the tail end of the cantilever beam when the cantilever beam is regarded as a blunt body in the liquid, thereby leading the liquid at the tail end of the cantilever beam to generate turbulent flow to generate great differential pressure resistance, preventing the micro-cantilever beam from vibrating, and being difficult to collect good micro-cantilever beam vibration signals, leading to larger error for detection, leading to lower main beam 7b to be rotated by 90 degrees in the vertical direction, leading to the fact that the upper main beam 7a at the front end of the main beam and the lower main beam 7b at the rear end of the main beam are in a space orthogonal relation, leading to the lower main beam 7b at the rear end of the main beam to move in the liquid to perform shearing vibration, and leading to be regarded as a streamline body in the liquid because the contact area with the liquid is greatly reduced, the boundary layer separation phenomenon can not occur at the tail end of the beam, and the turbulent flow is not generated at the tail end of the beam, leading to generate differential pressure resistance not to be generated, thereby eliminating the detection error caused by differential pressure resistance and greatly improving the quality factor of detection; the magnetic adsorption layer and the insulating film 7c are tightly attached to the magnetic adsorption layer, and are used for preventing detection errors caused by the adsorption of sundries before the magnetic adsorption layer is used, and the magnetic adsorption layer is adhered to the lower main beam 7b of the R-shaped orthogonal cantilever beam and is used for adsorbing magnetic suspended matters in liquid.
By the way, in the embodiment, the STM32 control chip 11 of the control unit converts the digital signal into the analog signal through the digital-analog conversion chip 12 and transmits the analog signal to the operational amplifier 10, the operational amplifier 10 is controlled to excite the detection unit 7, the detection unit 7 transmits the detection signal to the ADC pin 13 and then transmits the detection signal back to the STM32 control chip 11 through the receiving unit, and the processing module of the STM32 control chip 11 performs signal processing and then transmits the signal to the output pin 5 for signal output; the control unit crystal oscillators 2 and 14 are used for providing basic clock signals for the system to mainly control the STM32 control chip 11, wherein the processing module is used for resolving to obtain additional mass and additional damping digital signals, transmitting the digital signals to the CAN interface chip and finally transmitting the digital signals to the external display to display the obtained additional mass and additional damping specific values.
The energy supply unit in the embodiment comprises two parts, wherein one part is an external computer power supply connected through a power supply pin 6, and the other part is an operation and discharge source chip 15 in a PCB circuit; the external computer power supply is used for supplying power to the whole PCB circuit so as to enable the whole PCB circuit to work normally; the operational amplifier 10 is individually supplied with power by the operational amplifier source chip 15.
The receiving unit in this embodiment is an ADC pin 13, and is mainly used for transmitting the detection signal of the detecting unit 7 to the STM32 control chip 11.
The voltage control unit in the embodiment comprises a schottky diode 16, an inductor 18, a capacitor 1, a resistor 9, a voltage stabilizer 17, a buck chip 3 and a boost chip; the schottky diode 16 is used for freewheeling and voltage stabilization to make the circuit work normally; the inductor 18 is used for storing energy and filtering so that the circuit works normally; the capacitor 1 is used for filtering and stabilizing voltage to enable the circuit to work normally; the resistor 9 is used for stabilizing current and dividing voltage so that the circuit works normally; the voltage stabilizer 17 is used for stabilizing voltage to enable the circuit to work normally; the voltage reduction chip 3 reduces the standard 5V voltage of an external computer to 3.3V to reach the standard voltage of normal operation of other circuit elements; the boosting chip comprises an operational amplifier 10 and an operational amplifier source chip 15; the operational amplifier chip 15 increases the standard 5V voltage of the external computer to 12V and supplies power to the operational amplifier 10; the operational amplifier 10 increases the 3.3V working standard voltage in the PCB to 10V and supplies power to the piezoelectric driving mechanisms 7g, 7h, 7f and 7d in the detection unit 7 to enable the vibration detection.
In this embodiment, the digital-to-analog conversion unit is a digital-to-analog conversion chip 12, which converts the digital signal of the STM32 control chip 11 into an analog signal and transmits the analog signal to the operational amplifier 10 to activate the detection unit 7.
The output unit in the embodiment comprises a CAN interface chip 4 and an external display pin header 5; the CAN interface chip 4 transmits the digital signals obtained by processing the STM32 control chip 11 to the external display through the external display pin header 5, and outputs the digital signals.
In this embodiment, the auxiliary beam 7e is added, so that the original beam structure is changed into a main and auxiliary beam structure, the upper main beam 7a and the lower main beam 7b are used as main beams, and the auxiliary beam 7e is used as an auxiliary beam. When the frequency corresponding to the first-order mode is applied to the beam, the upper main beam 7a can vibrate greatly; when a frequency corresponding to the second-order mode is applied to the beam, the sub-beam 7e vibrates greatly; the modes refer to the inherent vibration characteristics of the sensor system, the vibration of the system is decomposed and coupled into N orthogonal single-degree-of-freedom vibration systems, the N modes of the system are corresponding, and each mode has a specific inherent frequency. By setting the frequency ratio of the first-order mode to the second-order mode to 1:2, exciting the cantilever beam with a frequency corresponding to a first-order mode, outputting vibration information of the auxiliary beam (Gao Pinliang) 7e through the piezoelectric signal, and obtaining a first harmonic and a second harmonic after carrying out Fourier change on the Gao Pinliang signal, wherein frequencies corresponding to the first-order mode and the second harmonic respectively correspond to frequency values corresponding to the first-order mode and the second-order mode. When the mass is applied, the above operation is repeated for the high frequency, so that new frequency values corresponding to the first harmonic and the second harmonic can be obtained, and the frequency offset corresponding to the first harmonic and the frequency offset corresponding to the second harmonic obtained in the two previous and subsequent times are 1:2, thereby forming a frequency doubling mechanism. The frequency ratio of the frequency offset of the first harmonic and the second harmonic is regulated and controlled by controlling the frequency ratio of the first-order mode and the second-order mode, and the frequency doubling mechanism realizes the improvement of sensitivity.
Example 2
Step one: the STM 32-based control micro-resonant liquid magnetic suspended matter mass sensor is fixed on a three-dimensional moving platform, the three-dimensional moving platform is adjusted to enable the direction of a detection unit of the three-dimensional moving platform to be downward, the detection unit is in vertical relation with the horizontal plane of the experiment table, then the x direction and the y direction of the three-dimensional moving platform are fixed, and at the moment, the three-dimensional moving platform can only move in the vertical direction of a z axis.
Step two: and placing the liquid to be detected into a beaker, and adjusting the three-dimensional moving platform to submerge the front end of the detection unit into the liquid to be detected.
Step three: the STM 32-based control micro-resonant liquid magnetic suspended matter mass sensor is connected with an external computer through a data line by a power pin on a PCB circuit board, and power is supplied by an external power supply.
Step four: the PCB is electrified to work normally, and the STM32 control chip correspondingly controls the operational amplifier to input excitation voltage sweep frequency signals to the piezoelectric driving mechanism through the control module so as to drive the detection unit to vibrate integrally.
Step five: reading the voltage values of the upper main beam 7a, the lower main beam 7b and the auxiliary beam 7e during internal resonanceAnd the STM32 control chip 11 is used for carrying out Fourier transform processing to obtain the phases of the main beam and the auxiliary beam>According to the formula->Converting the voltage value to an amplitude +.>；
Step six: additional mass to liquid using constructed liquid mass sensing equationAdditional damping->The solution is performed and the derivation of the solution equation is as follows:
step seven: the solution equation in step six is derived as follows:
firstly, after immersing an R-shaped orthogonal micro-cantilever into liquid, establishing a motion equation to obtain:
formula 1;
formula 2;
then solving for the additional mass using a multiscale methodAdditional damping->：
Introducing small disturbance parameters=0.001，
Order the；
；
；
；
；
；
The approximate solution of the final periodic solution can be expressed as:
formula 3;
formula 4;
the external excitation is in the form ofcoswt，Therefore, it is- 、 />The phase difference of the responses of the low-frequency sensing beam and the high-frequency detecting beam is respectively calculated by +.>And->Indicating (I)>And->，/>And->Are equal in value to each other in terms of the number,/>、/>the phase parameter is used for representing the response phase difference of the cantilever beam;
wherein the method comprises the steps ofIs equivalent to the main beam in mass->Is equivalent mass of the auxiliary beam->Is the inherent damping of the main beam->Is the inherent damping of the secondary beam->For the vibration response of the main beam, +.>For the vibrational response of the secondary beam +.>Is the vibration amplitude of the main beam>For the vibration amplitude of the auxiliary beam +.>For the phase of the vibration of the main beam->For the phase of the vibration of the secondary beam +.>For the linear rigidity of the main beam->For the linear stiffness of the secondary beam +.>Is nonlinear rigidity>And->For the excitation frequency, is a coordinated quantity,for externally excited acceleration->Additional mass applied to the girder for the liquid, < >>Additional damping applied to the main beam for the liquid; />Is the vibration speed of the main beam, +.>The vibration speed of the auxiliary beam; />Is the vibration acceleration of the main beam, +.>The vibration acceleration of the auxiliary beam; w is the driving frequency applied to the cantilever, < >>For the response frequency of the main beam, < > is>The response frequency of the secondary beam; />Infinitesimal>Infinitesimal>Is infinitely small, t is time, +.>Is nonlinear stiffness;
5 type；
6 type；
7 type；
Formula 8;
wherein,is the vibration amplitude of the main beam>The vibration amplitude of the auxiliary beam is set; />And->Is the theoretical excitation frequency and is the coordination quantity;for the response frequency of the main beam, < > is>Response frequency of secondary beam, +.>Is nonlinear stiffness; />For externally excited acceleration->、Is a phase used for representing the response phase difference of the cantilever beamA bit parameter;
，（j，k=1,2）；
from equation 5 over equation 6:
formula 9;
similarly, the formula 7 is compared with the formula 8:
formula 10;
combining 7 and 8 to calculate the additional massAdditional damping->：
Formula 11;
formula 12;
due to the additional massAdditional damping->Except for the phase of the main beam and the auxiliary beam>、/>Displacement a with the main beam and the auxiliary beam,b, except the experimental result, the other parameters are constant, so that when the external environment is not changed, before the mass disturbance is not applied, the additional mass +.>Additional damping->And is a fixed value;
removing the insulating film on the magnetic adsorption layer, and allowing the detection unit to start adsorbing magnetic suspended substances in the liquidThe equation of motion at this time can be listed as:
；
；
the mass equation of the magnetic suspended matters can be obtained by using a multi-scale method:
formula 13;
formula 14;
neglecting the change in mass after application of the magnetic substance, it can be seen from the above that the mass is addedAdditional damping->For the fixed value, the nine and ten formulas are combined to know the quantity of the magnetic suspended substances>：
Formula 15;
wherein the method comprises the steps of，/>Is prepared from magnetic substance>Frequency of change, ++>Is prepared from magnetic substance>Varying phase.
Table 1 is the comparison of the R-shaped orthogonal cantilever beam after the application of different mass disturbances and without the application of mass disturbances in this example.
TABLE 1
After the output signal of the auxiliary beam obtained through experiments is subjected to Fourier transformation, the first harmonic and the second harmonic can be obtained. It can be seen from the table that when a mass disturbance of 0.7g is applied, the first harmonic (corresponding to the first order frequency of the cantilever) is shifted by 1Hz and the second harmonic (corresponding to the second order frequency of the cantilever) is shifted by 2Hz. Similarly, applying 0.7x2g,0.7x3g is also to follow the first harmonic offset by an amount, the second harmonic offset. When the detection is performed using a single beam, the resonance frequency shift amount of the detection beam after the disturbance is applied is not a double shift, compared with the single beam. According to the sensitivity, when certain disturbance is applied, namely the disturbance is unchanged, the sensitivity of the R-shaped orthogonal cantilever structure adopted by the invention for detecting the quality of the magnetic suspended matters is higher than that of the traditional single cantilever structure.
Referring to fig. 9, the detection unit is moved to the outside of the liquid through the three-dimensional moving platform, the residual liquid and the residual liquid magnetic suspended matters on the surface of the detection unit are cleaned, the insulating film is covered on the magnetic adsorption layer again, then an excitation voltage sweep signal is input to the piezoelectric driving mechanism, the detection unit is driven to vibrate wholly, and the vibration signal is recorded and output.
Then, the detection unit submerges the front end of the R-shaped orthogonal cantilever beam in liquid through the three-dimensional moving platform, an excitation voltage sweep frequency signal is input to the piezoelectric driving mechanism, the detection unit is driven to integrally vibrate, and a vibration signal is recorded and output. Referring to fig. 10, a comparison chart of the quality factors of the vibration signals in the air and the liquid in the present embodiment is obtained. Wherein the quality factor represents the sharpness of the voltage-frequency curve, and the sharper the curve indicates that the higher the quality factor of the vibration signal, the more stable the vibration signal.
Referring to fig. 10 and 11, finally, the quality factor comparison graphs of the vibration signals in the air and the liquid of the conventional micro-resonant sensor are compared. Wherein the conventional micro-resonant sensor uses a single beam having the same size as the main beam on the R-shaped orthogonal cantilever as the sensing core device. The detection environment is changed from air into liquid, the resistance of the liquid to the detection unit is inevitably increased, the peak value of the voltage-frequency curve in the two images is reduced, the sharpness is reduced to different degrees, but the differential pressure resistance is greatly reduced due to the adoption of the orthogonal structure at the front end of the R-shaped orthogonal cantilever beam, and compared with the traditional micro-resonance type sensor, the vibration signal quality factor of the micro-resonance type liquid magnetic suspended matter mass sensor based on STM32 control is greatly improved.
The present invention is not limited to the specific embodiments, and any person skilled in the art can easily think about the changes or substitutions within the technical scope of the present invention, and the changes or substitutions are included in the scope of the present invention. Therefore, the protection scope of the invention is subject to the protection scope of the claims.
Claims (8)
1. A magnetic suspension microresonator mass sensor in a liquid comprising: the device comprises a circuit board, a control unit, an energy supply unit, a receiving unit, a voltage control unit, a digital-to-analog conversion unit, an output unit and a detection unit, wherein the control unit is arranged on the circuit board through leads and pins and comprises a control chip and a crystal oscillator, the energy supply unit is used for supplying power to the circuit board, the receiving unit is used for transmitting detection signals of the detection unit to the control chip, the voltage control unit is used for changing the voltage to reach rated voltage of the circuit board and components, the digital-to-analog conversion unit is used for converting digital signals of the control chip into analog signals and transmitting the analog signals to an operational amplifier to excite the detection unit, the output unit is used for outputting signals, and the detection unit is used for collecting vibration signals in a liquid.
Wherein, the orthogonal micro-cantilever of R shape includes: the device comprises an upper main beam, a lower main beam and an auxiliary beam, wherein the upper main beam and the lower main beam are rectangular plate-shaped, the auxiliary beam is arranged on one side of the main beam and is integrally formed with the upper main beam, the upper main beam is fixedly connected with the lower main beam and is vertically arranged, a piezoelectric driving mechanism and a vibration pickup mechanism are arranged at the upper end of the upper main beam, the vibration pickup mechanism is arranged at a position, close to the upper main beam, on the auxiliary beam, a magnetic adsorption layer and an insulating film tightly attached to the magnetic adsorption layer are adhered to the lower main beam, and the piezoelectric driving mechanism and the vibration pickup mechanism comprise: a positive electrode plate connected with the positive electrode, a negative electrode plate connected with the negative electrode, and piezoelectric materials positioned below the positive electrode plate and the negative electrode plate;
the R-shaped orthogonal cantilever girder is subjected to rotation treatment at two thirds to form an upper girder and a lower girder, so that the upper girder and the lower girder form an orthogonal relationship in space, the lower girder moves in liquid to perform shearing vibration, and the contact area with the liquid is reduced;
the piezoelectric driving mechanism and the vibration picking mechanism on the upper main beam share a negative electrode plate, and the electrode plates of the piezoelectric driving mechanism and the vibration picking mechanism on the upper main beam are arranged at the edge of the upper end of the main beam and are arranged at two sides of the negative electrode plate in parallel;
the positive electrode plate and the negative electrode plate of the vibration pickup mechanism positioned on the auxiliary beam are arranged on the auxiliary beam at a position close to the upper main beam;
the positive electrode plate and the negative electrode plate of the piezoelectric driving mechanism drive the upper girder, the lower girder and the auxiliary girder to vibrate through the power supply of the operational amplifier, the positive electrode plate and the negative electrode plate of the vibration pickup mechanism on the upper girder and the auxiliary girder convert vibration signals into voltage signals and transmit the voltage signals to ADC pins of the receiving unit, and the receiving unit transmits the voltage signals to the control chip for signal identification.
2. The micro-resonant mass sensor of claim 1, wherein the upper main beam vibrates when the piezoelectric driving mechanism applies a frequency corresponding to a first-order mode to the R-shaped orthogonal micro-cantilever by adding an auxiliary beam to the upper main beam; when the piezoelectric driving mechanism applies a frequency corresponding to a second-order mode to the R-shaped orthogonal micro-cantilever, the auxiliary beam vibrates; the first-order mode and the second-order mode refer to vibration frequencies set by the sensor, vibration of the piezoelectric driving mechanism is decomposed and coupled into a plurality of orthogonal single-degree-of-freedom vibrations, the vibration corresponds to a plurality of modes of the sensor, each mode has a natural frequency, and the frequency ratio corresponding to the first-order mode and the second-order mode is set to be 1:2, exciting the R-shaped orthogonal micro cantilever by the piezoelectric driving mechanism at a frequency corresponding to a first-order mode, outputting a piezoelectric signal of the auxiliary beam through the vibration pickup mechanism, and obtaining a first harmonic wave and a second harmonic wave after Fourier change is carried out on the piezoelectric signal of the auxiliary beam, wherein frequencies corresponding to the first-order mode and the second harmonic wave correspond to frequency values corresponding to the first-order mode and the second-order mode respectively; when the R-shaped orthogonal micro-cantilever beam is applied with mass, repeating the above operation to obtain new frequency values corresponding to the first harmonic and the second harmonic, wherein the frequency offset corresponding to the first harmonic and the frequency offset corresponding to the second harmonic obtained in the front and the back is 1:2, thereby forming a frequency multiplication mechanism, and regulating and controlling the frequency ratio of the frequency offset of the first harmonic and the second harmonic by controlling the frequency ratio of the first-order mode and the second-order mode.
3. The micro-resonance type mass sensor for the magnetic suspended matters in the liquid according to claim 1, wherein the control chip converts a digital signal into an analog signal through the digital-analog conversion unit and transmits the analog signal to the operational amplifier, controls the operational amplifier to excite the detection unit, transmits the detection signal to the receiving unit, and then transmits the detection signal back to the STM32 control chip through the receiving unit, and transmits the detection signal to the output unit for signal output after the signal is processed through the processing module of the STM32 control chip; the control unit crystal oscillator is used for providing a basic clock signal, the processing module is used for resolving and obtaining additional mass and additional damping digital signals, the digital signals are transmitted to the CAN interface chip, and finally the CAN interface chip is transmitted to the external display to display the obtained additional mass and additional damping specific values.
4. The magnetic suspended matter microresonator mass sensor of claim 1, where the power supply unit comprises an external power source and an operational discharge source chip inside a circuit board; the external power supply is used for supplying power to the circuit board to enable the circuit board to work normally; the operational amplifier is connected with the operational amplifier through the operational amplifier source chip.
5. The magnetic suspended matter microresonator mass sensor of claim 1, where the receiving unit comprises a power pin, an output pin, and an ADC pin; the ADC pin header is used for transmitting detection signals of the detection unit to the control chip, the power pin header is used for connecting a power end, and the output pin header is used for being connected with the output unit.
6. The magnetic suspended matter microresonator mass sensor of claim 1, where the voltage control unit comprises a schottky diode, an inductor, a capacitor, a resistor, a voltage stabilizer, a buck chip, a boost chip; the Schottky diode is used for freewheeling and stabilizing voltage to enable the circuit to work normally; the inductor is used for storing energy and filtering so that the circuit works normally; the capacitor is used for filtering and stabilizing voltage to enable the circuit to work normally; the resistor is used for stabilizing current and dividing voltage to enable the circuit to work normally; the voltage stabilizer is used for stabilizing voltage to enable the circuit to work normally; the voltage reduction chip reduces the standard 5V voltage of an external computer to 3.3V; the boosting chip comprises an operational amplifier and an operational amplifier; the operation and discharge source chip increases the standard 5V voltage of an external computer to 12V and supplies power to the operational amplifier; the operational amplifier increases the 3.3V working standard voltage in the circuit board to 10V and supplies power to the piezoelectric driving mechanism in the detection unit so as to detect vibration.
7. The micro-resonant mass sensor of claim 1, wherein the digital-to-analog conversion unit comprises a digital-to-analog conversion chip for converting the digital signal of the control chip into an analog signal and transmitting the analog signal to the operational amplifier to activate the detection unit.
8. The magnetic suspended matter microresonator mass sensor in liquid of claim 1, characterized in that the output unit comprises a CAN interface chip and an external display pin header; and the CAN interface chip transmits the digital signals processed by the control chip to the external display through the external display pin header to output the digital signals.
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