A VOCs concentration distribution monitoring system in a spray booth

Abstract

This invention relates to the field of substance concentration measurement technology and discloses a VOCs concentration distribution monitoring system in a spray booth, including a feature detection module, a signal receiving module, a pneumatic protection module, a concentration inversion module, and a differential pressure adjustment module. The signal receiving module receives the transmitted signal through a central detector and captures the forward scattered signal using a ring detection array. The concentration inversion module determines the particle size shift of paint mist particles during the phase transition process based on the ratio of transmitted to scattered light intensity, thereby correcting the extinction section parameter in real time and outputting concentration data. The differential pressure adjustment module maintains a slightly positive pressure inside the pneumatic protection module that is 5 Pa to 15 Pa higher than the ambient static pressure. This invention utilizes the scattering physical characteristics to offset the measurement error caused by the nonlinear attenuation of paint mist particle size in situ, effectively eliminating the optical path signal interference caused by droplet evaporation in a multiphase flow field.

Description

Technical Field

[0001] This invention belongs to the field of substance concentration measurement technology, and in particular relates to a VOCs concentration distribution monitoring system in a spray booth. Background Technology

[0002] Currently, the monitoring of organic waste gas generated in industrial spraying workshops typically employs contact sensor arrays or extraction sampling systems. These solutions rely on sensor diffusion or negative pressure suction to acquire the components to be measured. However, the spraying chamber contains high concentrations of multiphase fluids, and paint mist particles can easily clog the sensor's inlet membrane or sampling pipeline during migration, leading to nonlinear attenuation of detection efficiency and signal hysteresis. To overcome droplet contamination, conventional methods employ multi-stage filtration devices, but the filtration process prolongs the mass transfer time of the sampled gas, and the homogenization effect within the gas chamber eliminates the spatial distribution characteristics of the gas, making it impossible to identify the risk of combustion and explosion caused by instantaneous local accumulation.

[0003] Existing technologies have shortcomings in monitoring pipeline control and maintenance logic. For example, Chinese invention patent CN223513202U discloses an online monitoring device for VOCs gas treatment. This device constructs a circulating sampling loop using an electromagnetic flow valve and a gas pump, and utilizes a return pipeline to remove residual gas and improve monitoring accuracy. However, this solution is based on conventional gaseous pollutant sampling and treatment. When faced with the unique high-viscosity, variable-particle-size, multiphase flow field of a spray painting booth, the sampling logic is constrained by the physical environment. High-viscosity paint mist droplets enter the sampling branch pipe and become wetted and adhered, resulting in physical blockage at a rate exceeding [a certain threshold]. The high response frequency of the aerodynamic cleaning mechanism renders the backflow cleaning logic ineffective in paint mist environments. This type of point sampling lacks the ability to resolve VOC concentration gradients within the flow field on a spatial scale, making it difficult to capture instantaneous concentration peaks caused by phase transitions in non-equilibrium flow fields. Existing open optical path monitoring methods typically convert concentration signals using the ratio of light intensity between the reference wavelength and the characteristic absorption wavelength in an attempt to eliminate particulate extinction interference. However, in a dynamically volatile multiphase flow field, the Mie scattering cross-section of paint mist particles fluctuates nonlinearly with the phase transition of particle size, resulting in unpredictable zero-point drift of the measurement baseline.

[0004] Therefore, the technical problem to be solved by this invention is how to achieve high-fidelity reconstruction of the three-dimensional distribution of VOCs concentration in a dynamic flow field containing high concentrations of viscous paint mist and complex aerodynamic disturbances. Summary of the Invention

[0005] This invention provides a VOCs concentration distribution monitoring system in a spray booth, comprising: The feature detection module is used to project a multi-chord infrared feature detection laser beam into the monitoring area of ​​the spraying work space at a preset driving frequency; The signal receiving module is used to perform spatial topological sampling of the photon energy passing through the flow field to be measured. The signal receiving module includes a central detector and a ring detector array concentrically surrounding the central detector. The central detector is used to receive the transmitted light intensity signal in the direction of the optical axis, and the ring detector array is used to capture the forward scattered light intensity signal generated by paint mist particles. The pneumatic protection module is used to form a wall-attached laminar flow protective air curtain at the optical interface between the feature detection module and the signal receiving module. The pneumatic protection module is equipped with a jet channel and an environmental static pressure sampling hole. The concentration inversion module is used to calculate the ratio of the intensity of the forward scattered light signal to the intensity of the transmitted light signal, and to determine the equivalent particle size offset of the paint mist particles during the volatilization phase change process based on the intensity ratio. The equivalent particle size offset is used to correct the extinction section parameter in the absorbance calculation model, thereby outputting VOCs concentration data after physical decoupling. The differential pressure adjustment module is used to obtain the real-time differential pressure between the ambient static pressure collected by the ambient static pressure sampling hole and the internal pressure of the pneumatic protection module, and to adjust the opening of the control valve of the protective air source so that the internal pressure of the pneumatic protection module is constantly higher than the ambient static pressure of the spray booth by 5Pa to 15Pa. The positive pressure difference generated is used to block the mass transfer and diffusion of high-viscosity paint mist particles to the optical interface.

[0006] Preferably, the concentration inversion module is used to calculate the dynamic particle size distribution function of paint mist particles during the volatilization process by utilizing the multi-ring scattered light intensity distribution captured by the ring detector array; the concentration inversion module is used to retrieve the preset material scattering matrix according to the dynamic particle size distribution function and update the background extinction operator in the gas concentration inversion logic in real time, so as to remove the measurement baseline drift caused by droplet phase change in the non-equilibrium flow field of nonlinear decay of paint mist particle size, and obtain the true intrinsic absorbance of VOCs molecules after physical compensation.

[0007] Preferably, the differential pressure regulation module includes a differential pressure sensing unit. The first sampling end of the differential pressure sensing unit is led to the interior space of the spray booth through an ambient static pressure sampling hole, and the second sampling end of the differential pressure sensing unit is connected to the interior of the pneumatic protection module. The differential pressure regulation module is used to adjust the adjustment step frequency of the control valve according to the differential pressure fluctuation fed back by the differential pressure sensing unit, so as to counteract the paint mist entrainment interference caused by the air pressure pulsation of the spray booth exhaust system and maintain the stable state of the wall-mounted laminar flow protective air curtain.

[0008] Preferably, the concentration inversion module includes an occlusion removal unit, which is used to establish the correlation mapping between the geometric coordinates of the optical path channel and the motion trajectory of the spraying robot arm; when the infrared feature detection laser beam is blocked by the spraying robot arm, causing the transmitted light intensity signal to drop into the environmental noise range, the occlusion removal unit is used to update the weight distribution coefficient of the absorbance inversion matrix and reconstruct the absorbance data according to the concentration gradient evolution rate of adjacent effective optical path channels.

[0009] Preferably, the concentration inversion module further includes a concentration field reconstruction unit, which is used to generate a three-dimensional concentration distribution field of the monitoring area based on the corrected absorbance of multiple detection nodes; the concentration field reconstruction unit determines the high concentration accumulation area of ​​VOCs in the monitoring space and its diffusion vector direction by identifying the concentration peak coordinates in the three-dimensional concentration distribution field.

[0010] Preferably, the feature detection module includes a multi-wavelength emission unit for synchronously emitting a probe band laser located in the characteristic absorption spectrum of VOCs and a reference band laser located in the non-absorption spectrum; the concentration inversion module eliminates the absorption interference of water vapor components in the flow field to be measured on the VOCs measurement results by comparing the difference in light intensity attenuation rate between the probe band laser and the reference band laser.

[0011] Preferably, the jet channel of the pneumatic protection module is composed of multiple microholes evenly distributed circumferentially, and the central axis of each microhole forms an angle of 20° to 40° with the projection direction of the infrared feature detection laser beam, so as to guide the protective airflow to form a spiral outward diffused positive pressure jet layer on the lens surface of the optical interface.

[0012] Preferably, the concentration inversion module is also used to monitor the light intensity transmittance reference value of the central detector, and send a pulse boosting command to the differential pressure regulation module when the light intensity transmittance reference value is lower than 85%; the differential pressure regulation module is used to respond to the pulse boosting command, instantaneously increase the opening of the control valve, and remove the deposits on the outlet interface of the pneumatic protection module through the generated high-speed impact airflow.

[0013] Preferably, the system also includes a self-diagnostic module, which is used to obtain the standard deviation fluctuation index of the valve position feedback value of the control valve and the output of the concentration inversion module; the self-diagnostic module is used to calculate the response delay of the valve position feedback value relative to the real-time differential pressure, evaluate the pressure compensation dynamic characteristics of the pneumatic protection module, and output a system maintenance warning signal when the response delay exceeds 500ms.

[0014] Compared with existing technologies, the VOCs concentration distribution monitoring system in the spray booth of this invention has the following advantages: 1. In the monitoring of VOCs concentration distribution in the spray booth, the system achieves synchronous acquisition of the spatial topology of undeflected transmitted light and forward scattered halo by concentrically setting a central transmission detector and an annular scattering detector in the photoelectric detection component, and physically limiting the receiving solid angle of the annular scattering detector to between 0.5 degrees and 3.0 degrees relative to the axis. This physical layout enables the calculation unit to objectively characterize the equivalent particle size offset state of paint mist particles in the measurement channel based on the real-time ratio of the central transmission light intensity to the outer ring scattered light intensity. This mechanism of capturing scattering information in situ based on the physical interface replaces the static differential assumption of constant extinction ratio of interfering particles in the traditional technology, eliminates the measurement baseline oscillation caused by nonlinear particle size decay during the evaporation phase change of paint mist droplets, and ensures the extraction of the true VOCs molecular absorbance in the non-equilibrium flow field of violent gas-liquid two-phase transformation.

[0015] 2. The system utilizes an isolation chamber, jet orifices, and static pressure feedback holes located on the outside of the optical array plate to construct an aerodynamic balance adjustment mechanism for pressure fluctuations in the main exhaust system of the spray booth. By connecting a differential pressure transmitter to obtain indoor static pressure parameters and simultaneously adjusting the opening of the regulating valve of the clean air source, the system maintains a clean air curtain in a laminar flow state on the surface of the optical lens. This mechanism ensures that the stagnation pressure of the jet air curtain and the ambient pressure of the spray booth are always maintained at a set micro-positive pressure difference. This physically interrupts the mass transfer and adhesion process of high-viscosity paint mist particles to the optical interface. This dynamic pressure compensation scheme avoids the contamination of the measurement window by turbulent distortion caused by sudden changes in environmental static pressure, extends the maintenance-free operation cycle of the system, and ensures the long-term transmittance of the monitoring optical path.

[0016] 3. By spatially mapping the geometric topology of the meshed optical path channel with the motion coordinate parameters of the spraying arm, a dynamic mask removal and weight compensation mechanism for entity occlusion is established. When the robotic arm passes through the optical mesh, causing the transmitted light intensity of a specific optical path channel to drop into the environmental noise range, the calculation unit updates the spatial absorbance weight coefficient in real time and uses the concentration gradient evolution rate of adjacent effective channels for interpolation reconstruction. This processing logic solves the problem of unbalanced divergence of equations caused by traditional tomography algorithms when encountering dynamic entity interference. This allows the system to output a continuous concentration distribution topology map without interrupting monitoring during production operations, accurately identifying the transient combustion and explosion risk caused by local VOCs accumulation. Attached Figure Description

[0017] Figure 1 This invention provides a multi-module collaborative architecture and measurement and control flowchart for a VOCs concentration distribution monitoring system in a spray booth. Figure 2 This invention presents a fishbone diagram illustrating the multi-dimensional technical elements and control strategies for accurate monitoring of VOCs concentration in spray booths. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0019] It should be noted that all directional and positional terms used in this invention, such as: up, down, left, right, front, back, vertical, horizontal, inner, outer, top, bottom, transverse, longitudinal, center, etc., are only used to explain the relative positional relationship and connection between components in a specific state (as shown in the accompanying drawings). They are only for the convenience of describing this invention and do not require that this invention be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention. In addition, the descriptions of "first," "second," etc., in this invention are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0020] In the description of this invention, unless otherwise explicitly specified and limited, the terms installation, connection, and linking should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal connection of two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0021] In the description of this specification, references to the terms "an embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example, and the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0022] A VOCs concentration distribution monitoring system in a spray booth includes: The feature detection module is used to project a multi-chord infrared feature detection laser beam into the monitoring area of ​​the spraying work space at a preset driving frequency; The signal receiving module is used to perform spatial topological sampling of the photon energy passing through the flow field to be measured. The signal receiving module includes a central detector and a ring detector array concentrically surrounding the central detector. The central detector is used to receive the transmitted light intensity signal in the direction of the optical axis, and the ring detector array is used to capture the forward scattered light intensity signal generated by paint mist particles. The pneumatic protection module is used to form a wall-attached laminar flow protective air curtain at the optical interface between the feature detection module and the signal receiving module. The pneumatic protection module is equipped with a jet channel and an environmental static pressure sampling hole. The concentration inversion module is used to calculate the ratio of the intensity of the forward scattered light signal to the intensity of the transmitted light signal, and to determine the equivalent particle size offset of the paint mist particles during the volatilization phase change process based on the intensity ratio. The equivalent particle size offset is used to correct the extinction section parameter in the absorbance calculation model, thereby outputting VOCs concentration data after physical decoupling. The differential pressure adjustment module is used to obtain the real-time differential pressure between the ambient static pressure collected by the ambient static pressure sampling hole and the internal pressure of the pneumatic protection module, and to adjust the opening of the control valve of the protective air source so that the internal pressure of the pneumatic protection module is constantly higher than the ambient static pressure of the spray booth by 5Pa to 15Pa. The positive pressure difference generated is used to block the mass transfer and diffusion of high-viscosity paint mist particles to the optical interface.

[0023] Preferably, the concentration inversion module is used to calculate the dynamic particle size distribution function of paint mist particles during the volatilization process by utilizing the multi-ring scattered light intensity distribution captured by the ring detector array; the concentration inversion module is used to retrieve the preset material scattering matrix according to the dynamic particle size distribution function and update the background extinction operator in the gas concentration inversion logic in real time, so as to remove the measurement baseline drift caused by droplet phase change in the non-equilibrium flow field of nonlinear decay of paint mist particle size, and obtain the true intrinsic absorbance of VOCs molecules after physical compensation.

[0024] Preferably, the differential pressure regulation module includes a differential pressure sensing unit. The first sampling end of the differential pressure sensing unit is led to the interior space of the spray booth through an ambient static pressure sampling hole, and the second sampling end of the differential pressure sensing unit is connected to the interior of the pneumatic protection module. The differential pressure regulation module is used to adjust the adjustment step frequency of the control valve according to the differential pressure fluctuation fed back by the differential pressure sensing unit, so as to counteract the paint mist entrainment interference caused by the air pressure pulsation of the spray booth exhaust system and maintain the stable state of the wall-mounted laminar flow protective air curtain.

[0025] Preferably, the concentration inversion module includes an occlusion removal unit, which is used to establish the correlation mapping between the geometric coordinates of the optical path channel and the motion trajectory of the spraying robot arm; when the infrared feature detection laser beam is blocked by the spraying robot arm, causing the transmitted light intensity signal to drop into the environmental noise range, the occlusion removal unit is used to update the weight distribution coefficient of the absorbance inversion matrix and reconstruct the absorbance data according to the concentration gradient evolution rate of adjacent effective optical path channels.

[0026] Preferably, the concentration inversion module follows the following quantitative judgment rules when determining the real-time extinction correction coefficient: ,in, This is the real-time extinction correction factor. This is the forward-scattered light intensity signal. The transmitted light intensity signal is represented by α, which is a correction factor preset based on the refractive index of paint mist particles. The concentration inversion module is used to linearly decouple VOCs concentration data using real-time extinction correction coefficients.

[0027] Preferably, the concentration inversion module further includes a concentration field reconstruction unit, which is used to generate a three-dimensional concentration distribution field of the monitoring area based on the corrected absorbance of multiple detection nodes; the concentration field reconstruction unit determines the high concentration accumulation area of ​​VOCs in the monitoring space and its diffusion vector direction by identifying the concentration peak coordinates in the three-dimensional concentration distribution field.

[0028] Preferably, the feature detection module includes a multi-wavelength emission unit for synchronously emitting a probe band laser located in the characteristic absorption spectrum of VOCs and a reference band laser located in the non-absorption spectrum; the concentration inversion module eliminates the absorption interference of water vapor components in the flow field to be measured on the VOCs measurement results by comparing the difference in light intensity attenuation rate between the probe band laser and the reference band laser.

[0029] Preferably, the jet channel of the pneumatic protection module is composed of multiple microholes evenly distributed circumferentially, and the central axis of each microhole forms an angle of 20° to 40° with the projection direction of the infrared feature detection laser beam, so as to guide the protective airflow to form a spiral outward diffused positive pressure jet layer on the lens surface of the optical interface.

[0030] Preferably, the concentration inversion module is also used to monitor the light intensity transmittance reference value of the central detector, and send a pulse boosting command to the differential pressure regulation module when the light intensity transmittance reference value is lower than 85%; the differential pressure regulation module is used to respond to the pulse boosting command, instantaneously increase the opening of the control valve, and remove the deposits on the outlet interface of the pneumatic protection module through the generated high-speed impact airflow.

[0031] Preferably, the system also includes a self-diagnostic module, which is used to obtain the standard deviation fluctuation index of the valve position feedback value of the control valve and the output of the concentration inversion module; the self-diagnostic module is used to calculate the response delay of the valve position feedback value relative to the real-time differential pressure, evaluate the pressure compensation dynamic characteristics of the pneumatic protection module, and output a system maintenance warning signal when the response delay exceeds 500ms.

[0032] Example 1: When the system faces the non-equilibrium multiphase flow field conditions in the painting workshop of a large shipbuilding enterprise, the space is filled with dynamic airflow disturbances and high concentrations of viscous paint mist particles. The contact sensor experiences nonlinear attenuation of detection efficiency and signal hysteresis within a few hours due to droplet blockage of the air intake film. When conventional open optical path monitoring equipment encounters the pulse jet of the spray gun, the internal solvent of the paint mist droplets rapidly evaporates during high-speed flight and collision with the wall, causing high-frequency nonlinear attenuation of geometric dimensions. Particles in this dynamic evolution range produce a broadband extinction effect of Mie scattering that oscillates nonlinearly with wavelength on the detection beam. Conventional dual-wavelength differential algorithms rely on the static assumption of constant particle extinction ratio, causing the instrument to judge the abrupt change in droplet scattering phase as the peak value of VOCs gas concentration, triggering an explosion alarm and causing an unplanned shutdown of the safety interlock.

[0033] In this embodiment, a multi-chord infrared feature detection laser beam is projected onto the monitoring area by a feature detection module. A signal receiving module on the opposite side collects the spatial topological distribution characteristics of photon energy passing through the flow field under test. The signal receiving module includes a central detector and a ring detector array concentrically arranged around the central detector. The central detector receives the transmitted light intensity signal along the optical axis, and the ring detector array captures the forward scattered light intensity signal generated by the diffraction of paint mist particles. The concentration inversion module determines the equivalent particle size shift of the paint mist particles during the volatile phase transition process based on the intensity ratio of the forward scattered light intensity signal to the transmitted light intensity signal, and calculates the real-time extinction correction coefficient according to the following formula: ,in, This is the real-time extinction correction factor. It is a physical quantity representing the intensity signal of forward-scattered light. α is the physical quantity of transmitted light intensity signal, and α is a dimensionless correction factor set based on the refractive index of paint mist particles. The concentration inversion module uses this real-time extinction correction coefficient to correct the extinction section parameter in the absorbance calculation model, linearly decouples the VOCs concentration data, and removes the measurement baseline drift caused by droplet phase change in the non-equilibrium flow field of nonlinear decay of paint mist particle size, so as to obtain the true intrinsic absorbance of VOCs molecules after physical compensation.

[0034] The differential pressure regulation module continuously acquires the ambient static pressure collected through the ambient static pressure sampling port and the real-time pressure difference inside the pneumatic protection module. Based on the differential pressure fluctuations fed back by the differential pressure sensing unit, it synchronously adjusts the control valve to regulate the stepping frequency, counteracting the paint mist entrainment interference caused by the air pressure pulsation of the spray booth exhaust system. This keeps the internal pressure of the pneumatic protection module constant at 5 Pa to 15 Pa higher than the ambient static pressure of the spray booth. The positive pressure difference blocks the mass transfer and diffusion of high-viscosity paint mist particles to the optical interface, forming a wall-attached laminar flow protective air curtain at the optical interface. The morphological boundary conditions of this wall-attached laminar flow protective air curtain originate from the pre-executed flow... Wind tunnel simulation tests revealed that when the angle between the central axis of the uniformly distributed micropores within the aerodynamic protection module and the projection direction of the detection laser beam is set between 20° and 40°, the Reynolds number of the jet flow is below the critical threshold for the transition from laminar to turbulent flow. This ensures a stable, non-recirculating, spiral-shaped outward-diffusing jet layer on the lens surface. When the concentration inversion module detects that the light intensity transmittance reference value of the central detector is below 85%, it sends a pulse boosting command to the differential pressure regulation module. The differential pressure regulation module responds to the pulse boosting command by instantaneously increasing the opening of the control valve. The high-speed impact airflow removes the adhering substances from the outlet interface of the pneumatic protection module. The triggering timing of this pulse pressurization command is locked at the initial stage of the millisecond-level liquid phase spreading when the paint mist droplets hit the interface but the internal solvent has not yet completely evaporated and formed a film. The micro-shear force generated by the high-speed fluid physically peels off the resin molecules and optical mirrors before they form a stable chemical bond. When the movement trajectory of the spraying robot arm intersects with the infrared feature detection laser beam, causing the transmitted light intensity signal to drop into the environmental noise range, the occlusion removal unit inside the concentration inversion module establishes a correlation mapping between the geometric coordinates of the optical path channel and the movement trajectory of the spraying robot arm, updates the weight distribution coefficient of the absorbance inversion matrix, and reconstructs the absorbance data according to the concentration gradient evolution rate of adjacent effective optical path channels, maintaining the uninterrupted operation of the spatial inversion process. The in-situ capture action of the underlying photon scattering data and the dynamic positive pressure compensation mechanism of the aerodynamic boundary operate synchronously. The concentration field reconstruction unit included in the concentration inversion module generates a three-dimensional concentration distribution field of the monitoring area based on the absorbance corrected by multiple detection nodes. The concentration field reconstruction unit identifies the concentration peak coordinates in the three-dimensional concentration distribution field and outputs the VOCs high concentration accumulation area and diffusion vector direction in the monitoring space.

[0035] Example 2: In this example, the monitoring system is deployed in an environmental chamber simulating the multiphase flow field of a large ship painting workshop. The environmental chamber is equipped with a jet array to continuously inject paint mist droplets with a gradient shrinkage in particle size. The test signal source is superimposed with Gaussian white noise with a signal-to-noise ratio of 20dB and power frequency interference harmonics with a frequency of 50Hz. The differential pressure regulation module reads the environmental static pressure fluctuation feedback data obtained by the differential pressure sensing unit. When the wind pressure pulsation amplitude of the exhaust system approaches the 3Pa threshold, the differential pressure regulation module synchronously raises the control valve to adjust the step frequency, maintaining the wall-attached laminar flow protective air curtain at a pressure state 10Pa higher than the environmental static pressure, thus blocking the diffusion of paint mist particles to the optical interface.

[0036] A baseline concentration of 300 mg / m³ was continuously injected into the environmental chamber. The signal receiving module uses a concentric ring detector array to capture forward-scattered light intensity signals. The concentration inversion module reads the transmitted light intensity signal. With forward scattered light intensity signal A dimensionless correction factor α based on the refractive index of paint mist particles is set, and the concentration inversion module is based on the calculation formula. Calculate the real-time extinction correction factor The concentration inversion module utilizes real-time extinction correction coefficients. The extinction section parameter in the absorbance calculation model is updated based on the Lambert-Beer light intensity attenuation principle in non-uniform multiphase media. The concentration inversion module uses the real-time extinction correction coefficient. Perform the final concentration calculation according to the formula. To obtain real-time VOCs concentration data, among which Characterizes the actual concentration of VOCs after removing the interference of paint mist and matting effect. This refers to the absolute reference transmitted light intensity calibrated under a clean, paint-mist-free flow field during the system initialization phase. σ represents the intrinsic absorption coefficient of the solidified target VOCs gas in the local memory at the characteristic detection wavelength. L indicates the physical chord length crossed by the optical path channel within the spraying operation monitoring area. Addressing the physical fact that the intense evaporation phase transition of paint mist droplets causes nonlinear fluctuations in the characteristic cross-section of Mie scattering, a dynamic piecewise linearization calibration procedure is built-in, utilizing the signal receiving module to capture the forward scattered light intensity signal in real time. The absolute energy range defines the equivalent particle size attenuation window of the current paint mist droplet phase transition. The local tangent slope of the matching particle size evolution window is retrieved from the preset material scattering matrix and used as a dimensionless correction factor for the current calculation cycle. Relying on a multi-range high-frequency dynamic reload mechanism, the wide-range nonlinear physical phase transition attenuation is converted into a piecewise monotonically linear compensation mapping. The real-time VOCs concentration data output by the experimental group remained at 304.2 mg / m³. 3 Standard VOCs gas was used, and the paint mist spraying array was simultaneously activated. Three independent control groups were set up. The first control group used a static dual-wavelength differential method, without a ring detection array. Due to solvent evaporation, the equivalent particle size of the paint mist droplets shrank from 50 μm to 10 μm, and the concentration measurement value output by the first control group jumped to 451.8 mg / m³. 3The concentration deviated from the baseline by 50.6%. The second control group was equipped with a multi-chord infrared characteristic detection laser beam, and the positive pressure difference inside the aerodynamic protection module was set to 2 Pa. After continuous operation for 15.2 minutes, paint mist particles appeared to adhere to the optical interface, and the transmitted light intensity signal attenuated to the environmental noise range, triggering an optical path failure alarm. The experimental group adopted the technical solution of this invention. Under the same interference conditions, the signal receiving module of the experimental group used the central detector to obtain the transmitted light intensity signal in the optical axis direction passing through the flow field under test. 3 Up to 307.8 mg / m 3 The range corresponds to a measurement deviation of less than 2.6%.

[0037] Increasing the paint mist injection density in the environmental chamber reduced the light intensity transmittance benchmark value of the central detector to 15.1%, and the concentration measurement deviation of the test group output was 4.5%. Adjusting the control command of the differential pressure adjustment module made the internal pressure of the pneumatic protection module reach 25 Pa, generating jet vortices in the flow field and entraining local gas. The oscillation amplitude of the local VOCs concentration reading output by the system reached 18.5%. The above data comparison defined the pressure difference range of 5 Pa to 15 Pa as the engineering boundary for maintaining the flow field morphology and interface isolation. The system relies on the photoelectric hardware topology of extracting the intensity of the scattering halo to convert the extinction characteristics in the multiphase dynamic flow field into the extinction correction coefficient, thereby realizing the physical compensation for the drift of the measurement baseline.

[0038] Example 3: The system acquires a physical reference with a dimensionless correction factor α. A feature detection module and a signal receiving module are placed in the offline calibration chamber, which contains paint mist particles with a standard refractive index. The feature detection module emits a multi-chord infrared feature detection laser beam, and the central detector of the signal receiving module captures the transmitted light intensity signal. A concentric ring detector array captures forward-scattered light intensity signals. The calibration chamber control unit inputs standard VOCs gas with gradually increasing concentrations according to a time step. The time step is set to three times the response time of the signal receiving module. The concentration inversion module records the forward scattered light intensity signal at different standard concentrations. With transmitted light intensity signal The logarithmic ratio of the standard VOCs gas is used to establish a linear regression equation between the logarithmic ratio and the theoretical extinction cross-section parameter of the standard VOCs gas. In this calibration process, suspended standard refractive index paint mist particles provide a constant Mie scattering background in the offline calibration chamber, and the gradient-increasing standard VOCs gas only causes pure molecular absorption attenuation of the transmitted light intensity signal. This linear regression equation is essentially, under the physical boundary condition of locking constant liquid phase scattering interference, mathematically separating and quantifying the cross-coupling weight of particle forward scattering halo on the transmission light path extinction model through the independent variable of gas phase concentration. The concentration inversion module extracts the slope of the linear regression equation as the fixed value of the dimensionless correction factor α and writes it into the local memory. The above steps associate the dimensionless correction factor α with the optical scattering properties of the paint mist, providing a basis for calculating the real-time extinction correction coefficient. The input parameters.

[0039] When the spraying robot arm blocks the detection beam, the blocking rejection unit inside the concentration inversion module reads the three-dimensional geometric boundary dimensions of the spraying work space during the system initialization phase, establishes a global coordinate system containing the spatial vector equations of all multi-chord infrared feature detection laser beams, and receives the angle pulse signals from the encoders of the servo motors of each joint of the spraying robot arm through the industrial Ethernet bus. Based on the forward kinematics algorithm that maps the angle pulse signals to spatial displacement, it calculates the real-time three-dimensional spatial coordinates of the outer contour envelope cylinder of the spraying robot arm. The blocking rejection unit periodically calculates the spatial distance between the outer contour envelope cylinder and the spatial vector equations of each optical path. When the calculated distance between the outer contour envelope cylinder and a specific optical path channel is less than the collision tolerance, the blocking rejection unit determines that the specific optical path channel has entered the blocking warning state and locks the historical absorbance reference value of the specific optical path channel in the previous sampling period. The collision tolerance is set based on the product of the maximum movement speed of the spraying robot arm and the system sampling period.

[0040] The spraying robotic arm's physical interpenetration with the infrared feature detection laser beam results in transmitted light intensity signals. When the light falls into the ambient noise range, the occlusion removal unit detects the transmitted light intensity signal. If the light intensity falls below the light intensity threshold, the weight distribution coefficients of specific optical path channels are simultaneously updated to 0. The light intensity threshold is set to 5% of the unobstructed transmitted light intensity baseline value during system initialization. The system's built-in initial absorbance inversion matrix is ​​constructed based on the geometric intercepts of discrete voxels in the monitoring area intersecting with each multi-chord optical path. After zeroing the weights of specific obstructed optical paths, the occlusion removal unit uses algebraic reconstruction technology to adjust and re-normalize the remaining non-zero row vectors of the inversion matrix using relaxation factors to ensure the well-posedness of the reduced spatial tomography equations in mathematical solutions. The occlusion removal unit extracts the spatial geometric position of the obstructed optical path in the global coordinate system. The two nearest effective optical paths are used to read the real-time absorbance values ​​of the two effective optical paths at the current time node. The spatial difference quotient of the two real-time absorbance values ​​is calculated as the concentration gradient evolution rate. The occlusion removal unit multiplies the concentration gradient evolution rate by the spatial distance compensation value between the occluded optical path and the adjacent effective optical path, and superimposes it on the historical absorbance benchmark value to output the reconstructed local absorbance data. The concentration inversion module reads the reconstructed local absorbance data and updates the corresponding array elements in the absorbance inversion matrix. The concentration inversion module uses the spatial physical gradient characteristics of adjacent optical paths to reconstruct the missing data and maintain the continuity of the three-dimensional concentration distribution field generation process.

[0041] Example 4: When the monitoring system connects a new batch of paint mist resin material to the underlying architecture, the aerosol generator is activated in the offline calibration wind tunnel and injects single-component paint mist particles with a fixed gradient in particle size. The central detector of the signal receiving module and the ring detector array synchronously collect the transmitted light intensity signal at each particle size node. With forward scattered light intensity signal The concentration inversion module calculates the light intensity ratio sequence based on two sets of light intensity values. Addressing the ill-conditioned inverse problem of the Fredholm integral equation for the continuous distribution function of discrete multi-ring forward-scattered light intensity inversion, the module incorporates a non-negative least squares iterative solver. Using the light intensity ratio sequence as the input vector, it constrains the oscillation of the solution by setting a smoothing regularization parameter. After iterative convergence, it outputs the dynamic particle size distribution function corresponding to the current evaporation moment. Then, the concentration inversion module combines the wavelength parameters of the feature detection laser beam to calculate the Mie scattering phase function distribution series corresponding to different particle sizes. Considering the drastic dynamic variation of the complex refractive index caused by changes in the mixed solvent ratio during the evaporation of paint mist particles, the calculation of this phase function distribution series employs a Mie series expansion optical model based on the BHMIE algorithm. The particles are equivalent to dielectric spheres with uniform absorption boundaries to solve for the Legendre polynomial scattering coefficients. The concentration inversion module constructs a multidimensional mapping array based on the phase function distribution series and the light intensity ratio sequence. The system burns the multidimensional mapping array into memory and solidifies it as a preset material scattering matrix.

[0042] When a monitoring system equipped with a material scattering matrix is ​​connected to the newly built spray booth, the system triggers a baseline calibration procedure under clean air conditions where spraying operations have not started and the exhaust system is operating at full power. The feature detection module projects a multi-chord infrared feature detection laser beam through the work space and into the signal receiving module on the opposite side. The concentration inversion module continuously records the transmitted light intensity signal for multiple sampling periods. The reference waveform is obtained and the root mean square amplitude of the reference waveform is calculated as the initial environmental attenuation factor. The control unit compares the difference rate of the initial environmental attenuation factor of adjacent optical path channels and adjusts the elevation angle of the stepper motor at the bottom of the feature detection module until the difference rate converges to a fixed threshold range. The system records the locked spatial geometric collinear pose coordinates and the initial environmental optical attenuation baseline of the specific spray booth. Based on the dual-wavelength differential absorption spectrum decoupling principle, after the measurement and control process enters a stable operating cycle, the multi-wavelength emission unit of the feature detection module synchronously and alternately emits the detection band laser and the reference band laser. The center wavelength of the detection band laser is anchored to the characteristic absorption peak of VOCs, and the center wavelength of the reference band laser is... The signal receiver synchronously collects the transmission attenuation rate of the reference band light intensity relative to the initial environmental optical attenuation baseline, which is locked to the adjacent water vapor-specific absorption band and avoids the VOCs absorption cross-section. This rate is used as a quantitative characterization parameter for water vapor transient concentration. The ratio of the optical absorption cross-section constant of water vapor in the detection band to that in the reference band, which is pre-calibrated offline, is retrieved. The quantitative characterization parameter for water vapor transient concentration is multiplied by the ratio of the constant, and the equivalent water vapor absorbance component in the detection band is calculated. The water vapor absorbance component is subtracted from the total absorbance data obtained from the detection band, and the net absorbance base contributed by the VOCs molecules under test is output, thus eliminating cross-channel absorption crosstalk caused by the evaporation of water phase components on the infrared characteristic detection frequency band.

[0043] Example 5: When faced with the task of acquiring the VOCs concentration gradient distribution in three-dimensional space, the concentration inversion module includes a concentration field reconstruction unit that divides the physical monitoring area of ​​the spraying operation space into a discrete set of three-dimensional voxel grids. It acquires the geometric penetration intercept of each optical path channel in the multi-chord infrared feature detection laser beam within the corresponding voxel, sets the initial concentration parameter of each voxel to the ambient background concentration, and reads the value based on the real-time extinction correction coefficient. The total absorbance of each optical path is corrected by summing the current concentration parameter of the voxel passed through each optical path and the corresponding geometric transmission intercept. The theoretical predicted absorbance of each optical path is then calculated by summing the product of the current concentration parameter and the corresponding geometric transmission intercept of each voxel. The difference between the total absorbance of the measured path and the theoretical predicted absorbance is extracted. Based on the proportional weight of the geometric transmission intercept of each voxel to the total geometric length of a specific optical path, the difference is added back to the concentration parameter of the corresponding voxel. The forward calculation and reverse error allocation calculation are continuously iterated at a system clock cycle of 10ms until the absorbance difference of all optical paths converges to below the set convergence tolerance.

[0044] When faced with a situation where continuous multi-shift operation causes the central detector response to drift, the control unit receives a stop pulse signal from the spraying robot arm with a time span longer than 5 seconds during the preset interval of the spraying production line. Simultaneously, it reads the feedback level of the exhaust fan of the ventilation system operating at full load, determines that the flow field under test has returned to the initial clean state without paint mist, obtains the real-time junction temperature value fed back by the thermistor located inside the signal receiving module, records the background dark current reference of the central detector when the infrared feature detection laser beam light source is cut off, retrieves the temperature drift compensation coefficient corresponding to the current real-time junction temperature value based on the temperature compensation matrix written in the local memory, updates the initial environmental attenuation factor by multiplying the temperature drift compensation coefficient with the background dark current reference, and the concentration inversion module reads the updated initial environmental attenuation factor as the zero-point baseline for subsequent absorbance calculation. It relies on the physical compensation of the device temperature drift offset caused by long-term operation of the hardware by the state detection action during the interval.

[0045] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit of this application and the scope of protection of this invention, and all of these forms are within the protection scope of this application.

Claims

1. A VOCs concentration distribution monitoring system in a spray booth, characterized in that, include: The feature detection module is used to project a multi-chord infrared feature detection laser beam into the monitoring area of ​​the spraying work space at a preset driving frequency; The signal receiving module is used to perform spatial topological sampling of the photon energy passing through the flow field to be measured. The signal receiving module includes a central detector and a ring detector array concentrically surrounding the central detector. The central detector is used to receive the transmitted light intensity signal in the direction of the optical axis, and the ring detector array is used to capture the forward scattered light intensity signal generated by paint mist particles. The pneumatic protection module is used to form a wall-attached laminar flow protective air curtain at the optical interface between the feature detection module and the signal receiving module. The pneumatic protection module is equipped with a jet channel and an environmental static pressure sampling hole. The concentration inversion module is used to calculate the ratio of the intensity of the forward scattered light signal to the intensity of the transmitted light signal, and to determine the equivalent particle size offset of the paint mist particles during the volatilization phase change process based on the intensity ratio. The equivalent particle size offset is used to correct the extinction section parameter in the absorbance calculation model, thereby outputting VOCs concentration data after physical decoupling. The differential pressure adjustment module is used to obtain the real-time differential pressure between the ambient static pressure collected by the ambient static pressure sampling hole and the internal pressure of the pneumatic protection module, and to adjust the opening of the control valve of the protective air source so that the internal pressure of the pneumatic protection module is constantly higher than the ambient static pressure of the spray booth by 5Pa to 15Pa. The positive pressure difference generated is used to block the mass transfer and diffusion of high-viscosity paint mist particles to the optical interface.

2. The VOCs concentration distribution monitoring system in a spray booth according to claim 1, characterized in that, The concentration inversion module is used to calculate the dynamic particle size distribution function of paint mist particles during the volatilization process by using the multi-ring scattered light intensity distribution captured by the ring detector array. The concentration inversion module is used to retrieve the preset material scattering matrix according to the dynamic particle size distribution function and update the background extinction operator in the gas concentration inversion logic in real time. In the non-equilibrium flow field of nonlinear decay of paint mist particle size, the measurement baseline drift caused by droplet phase change is removed, and the true intrinsic absorbance of VOCs molecules after physical compensation is obtained.

3. The VOCs concentration distribution monitoring system in a spray booth according to claim 1, characterized in that, The differential pressure regulation module includes a differential pressure sensing unit. The first sampling end of the differential pressure sensing unit is led to the interior space of the spray booth through the ambient static pressure sampling port, and the second sampling end of the differential pressure sensing unit is connected to the interior of the pneumatic protection module. The differential pressure regulation module is used to adjust the adjustment step frequency of the control valve according to the differential pressure fluctuation fed back by the differential pressure sensing unit, so as to counteract the paint mist entrainment interference caused by the air pressure pulsation of the spray booth exhaust system and maintain the stable state of the wall-mounted laminar flow protective air curtain.

4. The VOCs concentration distribution monitoring system in a spray booth according to claim 1, characterized in that, The concentration inversion module includes an occlusion removal unit, which is used to establish the correlation mapping between the geometric coordinates of the optical path channel and the motion trajectory of the spraying robot arm. When the infrared feature detection laser beam is blocked by the spraying robot arm, causing the transmitted light intensity signal to drop into the environmental noise range, the occlusion removal unit is used to update the weight distribution coefficients of the absorbance inversion matrix and reconstruct the absorbance data according to the concentration gradient evolution rate of adjacent effective optical path channels.

5. The VOCs concentration distribution monitoring system in a spray booth according to claim 1, characterized in that, The concentration inversion module also includes a concentration field reconstruction unit, which is used to generate a three-dimensional concentration distribution field of the monitoring area based on the corrected absorbance of multiple detection nodes. The concentration field reconstruction unit identifies the high concentration accumulation area of ​​VOCs in the monitoring space and its diffusion vector direction by identifying the concentration peak coordinates in the three-dimensional concentration distribution field.

6. The VOCs concentration distribution monitoring system in a spray booth according to claim 1, characterized in that, The feature detection module includes a multi-wavelength emission unit, which is used to synchronously emit a probe band laser located in the characteristic absorption spectrum of VOCs and a reference band laser located in the non-absorption spectrum. The concentration inversion module eliminates the absorption interference of water vapor components in the flow field to be measured on the VOCs measurement results by comparing the difference in light intensity attenuation rate between the probe band laser and the reference band laser.

7. A VOCs concentration distribution monitoring system in a spray booth according to claim 1, characterized in that, The jet channel of the pneumatic protection module consists of multiple micro-holes evenly distributed circumferentially, and the central axis of each micro-hole forms an angle of 20° to 40° with the projection direction of the infrared feature detection laser beam, so as to guide the protective airflow to form a spiral outward diffused positive pressure jet layer on the lens surface of the optical interface.

8. A VOCs concentration distribution monitoring system in a spray booth according to claim 1, characterized in that, The concentration inversion module is also used to monitor the light intensity transmittance reference value of the central detector, and send a pulse boosting command to the differential pressure regulation module when the light intensity transmittance reference value is lower than 85%. The differential pressure regulation module is used to respond to the pulse boosting command, instantaneously increase the opening of the control valve, and remove the deposits on the outlet interface of the pneumatic protection module through the generated high-speed impact airflow.

9. A VOCs concentration distribution monitoring system in a spray booth according to claim 1, characterized in that, The system also includes a self-diagnostic module, which is used to obtain the standard deviation fluctuation index of the valve position feedback value and the output of the concentration inversion module. The self-diagnostic module is used to calculate the response delay of the valve position feedback value relative to the real-time differential pressure, evaluate the pressure compensation dynamic characteristics of the pneumatic protection module, and output a system maintenance warning signal when the response delay exceeds 500ms.

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