A device and method for detecting and evaluating mud cake on a cutter head of a shield machine

Abstract

This invention discloses a device and evaluation method for detecting mud cake on the cutterhead of a tunnel boring machine. The device includes a signal acquisition and preprocessing unit, several coaxial cylindrical array electrode systems, a wireless signal transmission unit, a wireless signal receiving unit, and a real-time imaging host computer. The signal acquisition and preprocessing unit includes a DDS signal generation circuit, a power amplifier transmission circuit, a receiving conditioning circuit, an acquisition and processing circuit, and a controller. This invention deeply integrates the soft and hard dual-focusing DC array measurement method with the coaxial cylindrical focusing / shielding detection electrode system through dual innovation in structural design and measurement mechanism. Structurally, it employs high-strength corrosion-resistant materials and a multi-layer sealing design to ensure the reliability and stability of the electrode system under complex working conditions.

Description

Technical Field

[0001] This invention belongs to the field of underground engineering shield tunneling technology, and specifically relates to a shield tunneling machine cutterhead mud cake detection device and evaluation method in this field. Background Technology

[0002] Tunnel boring machine (TBM) technology is increasingly widely used in underground engineering projects such as transportation, water conservancy and hydropower, and energy mining due to its advantages of safety, efficiency, energy conservation, and environmental protection. However, when TBMs are excavating in soft soil strata rich in clay, such as weathered mudstone, argillaceous sandstone, and residual soil layers, the fine particles that are cut and broken up are easily adhered to the cutterhead surface or the inner wall of the soil chamber by the continuous crushing of the soil and the heat generated by friction with the cutterhead, forming mud cakes. This can cause a significant increase in cutterhead torque and thrust, a decrease in propulsion speed, and accelerated cutter wear. In severe cases, it can lead to cutterhead jamming and overheating of the main bearing, making tunneling difficult, blocking the soil chamber, and endangering construction safety. Current mud cake detection methods commonly used in TBM construction mainly rely on indirect analysis and experience-based judgment of multi-source information, such as monitoring cutterhead temperature and cutter wear, analyzing abnormal states of torque, thrust, rotational speed, tunneling speed, and screw conveyor parameters, and manually observing and testing the properties of the excavated soil. These methods often rely on expert experience bases, simulation models, historical data, and preset thresholds for information fusion and state inference. Their accuracy is highly dependent on the precision of tool wear models, environmental variables, various threshold settings, and the completeness of empirical data, resulting in significant limitations. More importantly, traditional methods suffer from severe lag, failing to identify the formation process of mud cakes in real time and accurately, and also struggling to determine the specific location and size of the mud cakes. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a device and method for detecting and evaluating mud cake on the cutterhead of a tunnel boring machine, which can perceive and warn of the formation process of mud cake in real time and accurately during the tunneling process of the tunnel boring machine, thereby improving the safety and tunneling efficiency of tunneling construction.

[0004] The present invention adopts the following technical solution:

[0005] An improved device for detecting mud cake on the cutterhead of a tunnel boring machine includes a signal acquisition and preprocessing unit, several coaxial cylindrical array electrode systems, a wireless signal transmitting unit, a wireless signal receiving unit, and a real-time imaging host computer. The signal acquisition and preprocessing unit includes a DDS signal generation circuit, a power amplifier transmitting circuit, a receiving conditioning circuit, an acquisition processing circuit, and a controller. The controller is electrically connected to the power amplifier transmitting circuit through the signal generation circuit. The power amplifier transmitting circuit is connected in parallel with each electrode system. One end of the receiving conditioning circuit is connected in parallel with each electrode system, and the other end is electrically connected to the controller through the acquisition processing circuit. The wireless signal transmitting unit supplies power to the signal acquisition and preprocessing unit and communicates with the controller and the wireless signal receiving unit. The wireless signal receiving unit communicates with the real-time imaging host computer.

[0006] Furthermore, the DDS signal generation circuit includes a multi-channel direct digital frequency synthesizer (DDS) and a D / A conversion circuit; the power amplifier transmitting circuit includes a power drive circuit and a resonant network; the receiving conditioning circuit includes a time-division switching circuit, an impedance matching circuit, and a preamplifier conditioning circuit; the acquisition and processing circuit includes an anti-aliasing filter circuit and an A / D conversion circuit; and the controller is an MCU controller. The MCU controller is electrically connected to the resonant network in sequence through the D / A conversion circuit, the multi-channel direct digital frequency synthesizer (DDS), and the power drive circuit. The resonant network is connected in parallel with each electrode system. One end of the time-division switching circuit is connected in parallel with each electrode system, and the other end is electrically connected to the MCU controller in sequence through the impedance matching circuit, the preamplifier conditioning circuit, the anti-aliasing filter circuit, and the A / D conversion circuit. The MCU controller configures the timing of the time-division switching circuit through the SPI bus protocol and receives the signals acquired by each electrode system in a time-division manner.

[0007] Furthermore, the signal acquisition and preprocessing unit also includes a monitoring circuit, which includes a potential sampling circuit and an A / D conversion circuit. The power drive circuit is electrically connected to the MCU controller in sequence through the potential sampling circuit and the A / D conversion circuit.

[0008] Furthermore, the MCU controller configures the multi-channel direct digital frequency synthesizer (DDS) using the SPI bus protocol, generating analog sine wave excitation signals of different frequencies in real time. After being processed by the subsequent anti-aliasing filtering and signal conditioning circuit, the signals are sent to the power drive circuit. With the help of the time-division switching circuit, the analog sine wave excitation signals of different frequencies are output to the corresponding electrode system for transmission according to the logical timing.

[0009] Furthermore, correlation detection technology is employed in the MCU controller to first construct a reference waveform and then perform cross-correlation calculations:

[0010] Let the signal to be measured be ,in Useful signal Let the noise signal be unrelated to it; let the reference signal be... Its frequency With useful signals If they are consistent, then their cross-correlation function is... for:

[0011]

[0012] In the above formula, Let A be the time delay, and A be the amplitude of the signal to be measured. B is the phase of the signal to be measured, and B is the amplitude of the reference signal. The reference signal phase.

[0013] Furthermore, the electrode system adopts a multi-layered ring arrangement, from the inside out, consisting of the main emission electrode A0, the monitoring electrodes M1 and M2, the plate current emission electrodes A1, A2 and A3, the potential reference electrode N, and the current return electrode B. Each electrode is electrically isolated and structurally sealed by an insulating ring.

[0014] Furthermore, the power amplifier transmitting circuit synchronously drives the mainstream transmitting electrode A0 and the plate current transmitting electrodes A1, A2, and A3 to transmit the mainstream and plate current. Under the synergistic effect of the monitoring electrodes M1 and M2 and the monitoring circuit, the plate current forces the mainstream to flow out in a direction perpendicular to the electrode system and reach a certain depth. The combination of A0 and A1 has the shallowest detection depth, the combination of A0 and A1, A2 has a medium detection depth, and the combination of A0 and A1, A2, A3 has the deepest detection depth.

[0015] Furthermore, the electrode system is installed inside the cavity of the protective shell, and the cavity is filled with silicone oil. The rear end face of the protective shell is fixed to the inside of the cutter head with bolts, and several sealing rings are arranged on the inner wall and rear end face of the protective shell to perform graded sealing and insulation of the axial direction and end face.

[0016] Furthermore, a conductive spring sheet is installed at the bottom of the electrode system and a signal lead is welded on. The conductive spring sheet and the insulating ring are integrally molded using injection molding. The conductive spring sheet is mechanically locked to the protective shell through a pre-set stud hole on its rear end face. The signal lead passes through the hydraulic oil pipe inside the protective shell cavity and is connected to the Remo standard interface. The hydraulic oil pipe uses a gland seal structure to penetrate the protective shell.

[0017] An improved method for evaluating mud cake buildup on the cutterhead of a tunnel boring machine (TBM) involves: establishing a refined three-dimensional electromagnetic model integrating the tunneling strata, mud-mud cake, and electrode system structure using the COMSOL multiphysics coupling simulation platform; measuring the global electric field response of the mud cake's apparent resistivity, mud slurry's apparent resistivity, strata's apparent resistivity, and the evolution of the mud cake's thickness and distribution pattern under specific frequency sinusoidal signal excitation; generating a multidimensional forward modeling response database; and outputting calibration charts showing the relationship between the mud cake's apparent resistivity and thickness measured under different detection modes. Based on the calibrated mud cake apparent resistivity-thickness relationship in the multidimensional forward modeling response database, the mud cake's thickness range and growth trend are evaluated by matching the measured apparent resistivity curves.

[0018] The beneficial effects of this invention are:

[0019] The detection device disclosed in this invention is based on DC array measurement technology. By arraying various electrode systems on the surface of the cutterhead or the inner wall of the soil chamber, it directly detects the slag in front of the cutterhead panel and the slag retention area, and constructs a dynamic sensing network for the apparent resistivity characteristics of the slag. For the first time, it realizes direct, real-time and visual monitoring of the formation, location and thickness of mud cake, fundamentally solving the problems of early warning lag and identification ambiguity in existing indirect prediction methods. It helps to reveal the formation mechanism and distribution law of mud cake and has good application prospects.

[0020] The evaluation method disclosed in this invention innovatively integrates weak mixing signal extraction technology with hierarchical multi-parameter forward and inverse algorithms. It suppresses noise interference and extracts mixing signals through cross-correlation operations. Based on a three-dimensional refined electromagnetic model, it establishes a calibration relationship chart between parameters such as mud cake thickness and apparent resistivity. After introducing regularization constraints and iterative algorithms, it achieves multi-parameter synchronous high-precision inversion, which significantly improves the accuracy and reliability of mud cake parameter identification under complex working conditions.

[0021] This invention deeply integrates the soft and hard dual-focusing DC array measurement method with the coaxial cylindrical focusing / shielding detection electrode system through dual innovation in structural design and measurement mechanism. Structurally, it adopts high-strength corrosion-resistant materials and multiple sealing designs to ensure the reliability and stability of the electrode system under complex working conditions. In terms of measurement, it integrates hardware fast focusing and algorithm flexible compensation to ensure the compatibility and improvement of detection depth and detection resolution. Attached Figure Description

[0022] Figure 1 This is a block diagram of the detection device disclosed in this invention;

[0023] Figure 2 This is a schematic diagram of the electrode system in the detection device disclosed in this invention;

[0024] Figure 3This is a block diagram illustrating the principle of the cross-correlation weak mixing signal extraction algorithm. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] Example 1 addresses the problem of severely limited tunneling efficiency and increased engineering safety risks caused by mud cake formation on the cutterhead during shield tunneling. This example discloses a mud cake detection device for shield tunneling machine cutterheads. The device measures the change in apparent resistivity during the mud cake growth process using an electrode system. It employs a dual-drive hierarchical multi-parameter forward and inverse algorithm based on both physical and data principles to record the mud cake formation process, locate its distribution position, and calculate its thickness.

[0027] like Figure 1 As shown, the device includes a signal acquisition and preprocessing unit, several coaxial cylindrical array electrode systems, a wireless signal transmission unit, a wireless signal receiving unit, and a real-time imaging host computer. The signal acquisition and preprocessing unit is the core processing component of the detection device, including a DDS signal generation circuit, a power amplifier transmission circuit, a receiving conditioning circuit, an acquisition processing circuit, and a controller. The controller is electrically connected to the power amplifier transmission circuit through the signal generation circuit. The power amplifier transmission circuit is connected in parallel with each electrode system. One end of the receiving conditioning circuit is connected in parallel with each electrode system, and the other end is electrically connected to the controller through the acquisition processing circuit. The wireless signal transmission unit provides stable power to the signal acquisition and preprocessing unit and communicates with the controller and the wireless signal receiving unit. The wireless signal receiving unit communicates with the real-time imaging host computer.

[0028] The electrode system employs a combination of multiple metal focusing / shielding electrodes and PEEK insulated electrodes to transmit DC excitation signals to the formation and simultaneously acquire voltage and current feedback signals carrying information on mud cake growth.

[0029] The electrode system, which is arranged at different positions on the cutterhead of the tunnel boring machine, collects information on the growth of mud cake in key parts. The signal acquisition and preprocessing unit conditions and preprocesses the original detection signal, converts it into multi-mode apparent resistivity data, and after the data is structured and organized through the 485 bus protocol, it is packaged and transmitted to the signal wireless transmission unit.

[0030] The wireless signal transmitting unit mainly consists of a power supply circuit, a communication conversion circuit, an attitude measurement circuit, a wireless transmitting circuit, and a WIFI transceiver antenna, and is powered by a slip ring. The wireless signal transmitting unit is wired to the signal acquisition and preprocessing unit. After aggregating the detection data from the electrode systems at different locations, the wireless signal transmitting unit transmits the data wirelessly to the wireless signal receiving unit.

[0031] The signal wireless receiving unit mainly consists of a wireless receiving circuit, an MCU control module, and an Ethernet communication circuit, which is used to transmit the received data to the real-time imaging host computer via a wired Ethernet network.

[0032] After the real-time imaging host computer acquires the raw data transmitted by the signal wireless receiving unit via the network cable, it calls the built-in integrated hierarchical multi-parameter forward and inverse modeling algorithm to perform data analysis, processing and imaging calculations, and analyze the growth state and spatial distribution of the mud cake in real time. At the same time, it performs human-computer interaction to control the corresponding units to execute instructions and take actions.

[0033] The DDS signal generation circuit includes a multi-channel direct digital frequency synthesizer (DDS) and a D / A conversion circuit. The power amplifier transmitting circuit includes a power drive circuit and a resonant network. The receiving conditioning circuit includes a time-division switching circuit, an impedance matching circuit, and a preamplifier conditioning circuit. The acquisition and processing circuit includes an anti-aliasing filter circuit and an A / D conversion circuit. The controller is an MCU controller. The MCU controller is electrically connected to the resonant network in sequence through the D / A conversion circuit, the multi-channel direct digital frequency synthesizer (DDS), and the power drive circuit. The resonant network is connected in parallel with each electrode system. One end of the time-division switching circuit is connected in parallel with each electrode system, and the other end is electrically connected to the MCU controller in sequence through the impedance matching circuit, the preamplifier conditioning circuit, the anti-aliasing filter circuit, and the A / D conversion circuit. The MCU controller configures the timing of the time-division switching circuit through the SPI bus protocol and receives the signals acquired by each electrode system in a time-division manner.

[0034] The signal acquisition and preprocessing unit also includes a monitoring circuit, which includes a potential sampling circuit and an A / D conversion circuit. The power drive circuit is electrically connected to the MCU controller in sequence through the potential sampling circuit and the A / D conversion circuit.

[0035] DDS High-Precision Signal Generation and Power Drive Circuit: The MCU controller configures the multi-channel direct digital frequency synthesizer DDS (AD9959 module) using the SPI bus protocol. By reading and writing its 32-bit high-resolution control register, it generates analog sine wave excitation signals of different frequencies in real time. After being processed by the subsequent anti-aliasing filtering and signal conditioning circuit, the signals are sent to the power drive circuit PA12. With the help of the time-division switching circuit, the analog sine wave excitation signals of different frequencies are output to the corresponding electrode system for transmission according to the logical timing.

[0036] Cross-correlation weak mixed-frequency signal extraction algorithm: The pressure difference and current signals received by the electrode system, which are related to the cake growth information, are very weak and are combinations of noisy multi-frequency signals. Therefore, the analog-conditioned and digitally acquired signals are subjected to anti-aliasing filtering and oversampling. Correlation detection technology is used in the MCU controller, such as... Figure 3As shown, a reference waveform is first constructed, and then cross-correlation is performed to achieve noise suppression and separation and extraction of weak mixing signals.

[0037] Let the signal to be measured be ,in Useful signal Let the noise signal be unrelated to it; let the reference signal be... Its frequency With useful signals If they are consistent, then their cross-correlation function is... for:

[0038]

[0039] In the above formula, Let A be the time delay, and A be the amplitude of the signal to be measured. B is the phase of the signal to be measured, and B is the amplitude of the reference signal. The reference signal phase.

[0040] It can be seen that for sinusoidal signals of the same frequency... and If the amplitude of one signal is known, the amplitude of the other signal can be determined using the cross-correlation function. Utilizing the statistical incorrelation between noise and the reference signal, noise can be effectively suppressed and processed through correlation operations, avoiding interference from noise when directly measuring the useful signal.

[0041] Coaxial cylindrical focusing / shielding detector electrode system: such as Figure 2 As shown, the electrode system adopts a multi-layer ring arrangement, from the inside to the outside, namely the main emission electrode A0, the monitoring electrodes M1 and M2, the plate current emission electrodes A1, A2 and A3, the potential reference electrode N, and the current return electrode B. Each electrode is electrically isolated and structurally sealed by an insulating ring.

[0042] The focusing / shielding electrode ring is made of TC11 high-strength titanium alloy and galvanized. It can operate at temperatures up to 500℃, has high strength and good wear resistance, and exhibits good corrosion resistance to mud and acid / alkali media in complex geological environments. The isolation and insulation ring is made of glass fiber reinforced engineering plastic polyetheretherketone (PEEK), which has excellent mechanical properties and superior chemical corrosion resistance. It has high insulation, good sealing performance, and low compression deformation at high temperatures.

[0043] The measurement method uses a dual-focusing DC array: hardware focusing adjusts the ratio of the main current of the main emitting electrode A0 to the plate current of the plate current electrodes A1, A2, and A3 using an external focusing circuit, forcing the potential difference between the two monitoring electrodes M1 and M2 to dynamically approach zero. Software focusing, based on digital signal processing technology, weights and superimposes two similar, independent, unfocused measurements (V voltage, I current), and uses an algorithm to compensate for the residual potential difference between the monitoring electrodes. Hardware focusing offers fast response and strong real-time performance, but it relies on analog feedback circuits, is susceptible to noise interference, and carries the risk of system oscillation. Software focusing allows for flexible configuration of focusing conditions, avoiding the system oscillation risk caused by hardware closed-loop feedback, but it relies on signal processing timing, has inherent delays, poor real-time performance, high requirements for synchronization between the two measurements, and is more sensitive to operating conditions.

[0044] This embodiment innovatively combines circuit hardware focusing with digital software focusing and drives a multi-layer annular array electrode to achieve a complementary effect in apparent resistivity measurement.

[0045] The measurement principle of the electrode system is as follows: When the detection device is working, the power amplifier transmitting circuit (power-controlled current source) synchronously drives the mainstream transmitting electrode A0 and the screen current transmitting electrodes A1, A2, and A3 to emit the mainstream and screen current. Under the synergistic effect of the monitoring electrodes M1 and M2 and the monitoring circuit, the screen current forces the mainstream to flow out in a direction perpendicular to the electrode system and reach a certain depth. Different combinations of shielding electrodes A1, A2, and A3 result in different detection depths. The combination of A0 and A1 results in the shallowest detection depth, the combination of A0 and A1 / A2 results in a medium detection depth, and the combination of A0 and A1 / A2 / A3 results in the deepest detection depth.

[0046] The detection depth is directly affected by the physical properties of the mud cake, such as its thickness, moisture content, density, and composition. The growth dynamics of the mud cake can be monitored by measuring the apparent resistivity of the mud cake under different modes.

[0047] The electrode system is installed inside the cavity of the protective shell, which is then filled with silicone oil for pressure equalization and isolation. The electrode system is installed from the inside of the tunnel boring machine outwards. The rear end face of the protective shell is fixed to the inside of the cutterhead with bolts. Several sealing rings are arranged on the inner wall and rear end face of the protective shell for graded sealing and insulation along the axial direction and at the end face. The protective shell is made of 05Cr17Ni4Cu4Nb type galvanized stainless steel, which has high strength and good toughness. While improving the lightweight and economic efficiency of the device, it also has good resistance to water vapor, mud, weak acids, weak alkalis, and salts.

[0048] A conductive spring sheet is installed at the bottom of the electrode system and a signal lead is welded on. The conductive spring sheet and the insulating ring are integrally molded using injection molding. The conductive spring sheet is mechanically locked to the protective shell through a pre-set stud hole on its rear end face. The signal lead passes through the hydraulic oil pipe inside the protective shell cavity and is connected to the Remo standard interface. The hydraulic oil pipe uses a gland seal structure to penetrate the protective shell.

[0049] This embodiment also discloses a method for evaluating mud cake buildup on the cutterhead of a tunnel boring machine (TBM) (a graded multi-parameter forward and inverse modeling algorithm). Based on the COMSOL multiphysics coupling simulation platform, a refined three-dimensional electromagnetic model integrating the tunneling strata, mud-mud cake, and electrode system structure is established. By defining the electromagnetic properties of each medium layer, the current field control equation derived from Maxwell's electromagnetic field theory is solved. Under sinusoidal signal excitation at a specific frequency, the electrode system measures the global electric field response law of the mud cake's apparent resistivity, mud slurry's apparent resistivity, strata's apparent resistivity, mud cake thickness, and distribution morphology. After large-scale parameter scanning, a multi-dimensional forward modeling response database covering multiple working conditions and possessing clear physical interpretability is generated. A calibration relationship chart of mud cake's apparent resistivity and thickness measured under different detection modes is output. Based on the calibrated mud cake apparent resistivity-thickness relationship in the multi-dimensional forward modeling response database, the mud cake thickness range and growth trend are evaluated by matching the measured apparent resistivity curves.

[0050] Under initial constraints, based on the mud apparent resistivity, formation apparent resistivity and actual electromagnetic properties of the medium calculated by synchronous inversion, a regularization method and physical condition constraints are introduced to perform iterative optimization to reduce the residual between the measured data and the forward response, thereby improving the accuracy and repeatability of parameter identification.

Claims

1. A device for detecting mud cake buildup on the cutterhead of a tunnel boring machine, characterized in that: The system includes a signal acquisition and preprocessing unit, several coaxial cylindrical array electrode systems, a wireless signal transmission unit, a wireless signal receiving unit, and a real-time imaging host computer. The signal acquisition and preprocessing unit includes a DDS signal generation circuit, a power amplifier transmission circuit, a receiving conditioning circuit, an acquisition and processing circuit, and a controller. The controller is electrically connected to the power amplifier transmission circuit through the signal generation circuit. The power amplifier transmission circuit is connected in parallel with each electrode system. One end of the receiving conditioning circuit is connected in parallel with each electrode system, and the other end is electrically connected to the controller through the acquisition and processing circuit. The wireless signal transmission unit supplies power to the signal acquisition and preprocessing unit and communicates with the controller and the wireless signal receiving unit. The wireless signal receiving unit communicates with the real-time imaging host computer.

2. The shield machine cutterhead mud cake detection device according to claim 1, characterized in that: The DDS signal generation circuit includes a multi-channel direct digital frequency synthesizer (DDS) and a D / A conversion circuit. The power amplifier transmitting circuit includes a power drive circuit and a resonant network. The receiving conditioning circuit includes a time-division switching circuit, an impedance matching circuit, and a preamplifier conditioning circuit. The acquisition and processing circuit includes an anti-aliasing filter circuit and an A / D conversion circuit. The controller is an MCU controller. The MCU controller is electrically connected to the resonant network in sequence through the D / A conversion circuit, the multi-channel direct digital frequency synthesizer (DDS), and the power drive circuit. The resonant network is connected in parallel with each electrode system. One end of the time-division switching circuit is connected in parallel with each electrode system, and the other end is electrically connected to the MCU controller in sequence through the impedance matching circuit, the preamplifier conditioning circuit, the anti-aliasing filter circuit, and the A / D conversion circuit. The MCU controller configures the timing of the time-division switching circuit through the SPI bus protocol and receives the signals acquired by each electrode system in a time-division manner.

3. The shield machine cutterhead mud cake detection device according to claim 2, characterized in that: The signal acquisition and preprocessing unit also includes a monitoring circuit, which includes a potential sampling circuit and an A / D conversion circuit. The power drive circuit is electrically connected to the MCU controller in sequence through the potential sampling circuit and the A / D conversion circuit.

4. The shield machine cutterhead mud cake detection device according to claim 2, characterized in that: The MCU controller configures the multi-channel direct digital frequency synthesizer (DDS) using the SPI bus protocol, generating analog sine wave excitation signals of different frequencies in real time. After processing by the subsequent anti-aliasing filtering and signal conditioning circuit, the signals are sent to the power drive circuit. With the help of the time-division switching circuit, the analog sine wave excitation signals of different frequencies are output to the corresponding electrode system for transmission according to the logical timing.

5. The shield machine cutterhead mud cake detection device according to claim 2, characterized in that: In the MCU controller, correlation detection technology is used to first construct a reference waveform and then perform cross-correlation calculations: Let the signal to be measured be ,in Useful signal Let the noise signal be unrelated to it; let the reference signal be... Its frequency With useful signals If they are consistent, then their cross-correlation function is... for: In the above formula, Let A be the time delay, and A be the amplitude of the signal to be measured. B is the phase of the signal to be measured, and B is the amplitude of the reference signal. The reference signal phase.

6. The shield machine cutterhead mud cake detection device according to claim 3, characterized in that: The electrode system adopts a multi-layered ring arrangement, from the inside to the outside: the main emission electrode A0, the monitoring electrodes M1 and M2, the plate current emission electrodes A1, A2 and A3, the potential reference electrode N, and the current return electrode B. Each electrode is electrically isolated and structurally sealed by an insulating ring.

7. The shield machine cutterhead mud cake detection device according to claim 6, characterized in that: The power amplifier transmitting circuit synchronously drives the mainstream transmitting electrode A0 and the plate current transmitting electrodes A1, A2, and A3 to transmit the mainstream and plate current. Under the synergistic effect of the monitoring electrodes M1 and M2 and the monitoring circuit, the plate current forces the mainstream to flow out in a direction perpendicular to the electrode system and reach a certain depth. The combination of A0 and A1 has the shallowest detection depth, the combination of A0 and A1 / A2 has a medium detection depth, and the combination of A0 and A1 / A2 / A3 has the deepest detection depth.

8. The shield machine cutterhead mud cake detection device according to claim 6, characterized in that: The electrode system is installed inside the cavity of the protective shell and filled with silicone oil. The rear end face of the protective shell is fixed to the inside of the cutter head with bolts. Several sealing rings are arranged on the inner wall and rear end face of the protective shell to perform graded sealing and insulation of the axial direction and end face.

9. The shield machine cutterhead mud cake detection device according to claim 8, characterized in that: A conductive spring sheet is installed at the bottom of the electrode system and a signal lead is welded on. The conductive spring sheet and the insulating ring are integrally molded using injection molding. The conductive spring sheet is mechanically locked to the protective shell through a pre-set stud hole on its rear end face. The signal lead passes through the hydraulic oil pipe inside the protective shell cavity and is connected to the Remo standard interface. The hydraulic oil pipe uses a gland seal structure to penetrate the protective shell.

10. A method for evaluating mud cake buildup on the cutterhead of a tunnel boring machine, characterized in that: Based on the COMSOL multiphysics coupling simulation platform, a three-dimensional refined electromagnetic model integrating shield tunneling strata, mud-cake, and electrode system structure is established. Under the excitation of a sinusoidal signal at a specific frequency, the electrode system measures the global electric field response of the apparent resistivity of the cake, the apparent resistivity of the mud, the apparent resistivity of the strata, and the evolution of the thickness and distribution of the cake. A multi-dimensional forward modeling response database is generated, and calibration relationship charts of the apparent resistivity and thickness of the cake measured under different detection modes are output. Based on the apparent resistivity-thickness relationship of the mud cake calibrated in the multidimensional forward response database, the thickness range and growth trend of the mud cake are evaluated by matching the measured apparent resistivity curves.

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