Automobile bumper skin varnish spraying control method and system

Abstract

The application provides a kind of automobile bumper skin varnish spraying control method and system, the method includes the following steps: according to the assembly position of bumper skin and adjacent vehicle body outer covering, determine the corresponding appearance reference area and extract multi-scale target texture;Texture attenuation relationship is established using the wet film texture and solidification texture of calibration object;According to the candidate spraying parameter, spray width and curved surface data, the wet film appearance is predicted, the solidification texture is combined with the wet film thickness, effective leveling time and varnish flow capacity, and the target spraying parameter and uniform solidification entry time are determined in the candidate parameter that meets the equipment and film forming constraint.The actual texture of adjacent outer covering is used as the target in the application, which can consider the matching of different curved surface areas and different texture scales, reduce the situation of film thickness qualified but texture incoordination, reduce the risk of local sagging, texture mutation and repeated test spraying, improve the appearance coordination, batch consistency and process determination efficiency of complex curved surface spraying.

Description

Technical Field

[0001] This invention relates to the field of automotive bumper painting technology, and in particular to a method and system for controlling the spraying of clear varnish on automotive bumper skin. Background Technology

[0002] Car bumper panels are typically made of plastic and are assembled adjacent to other exterior body panels such as fenders, hoods, rear side panels, or trunk lids. To improve the weather resistance, scratch resistance, and appearance quality of the bumper panels, a clear coat is usually applied to the painted surface, followed by flash-drying and curing. The surface texture formed by the clear coat is affected by various factors, including spray gun parameters, bumper panel curvature, wet film thickness, flash-drying time, and curing temperature. Due to differences in base materials, surface shapes, and painting processes between the bumper panel and adjacent exterior body panels, even if they have similar colors and gloss levels, visible texture differences may occur due to variations in short-wave orange peel, medium-wave undulations, and long-wave appearance changes, affecting the overall vehicle appearance harmony.

[0003] Current bumper clear coat spraying processes typically set the spray gun trajectory, clear coat flow rate, and travel speed based on empirical parameters, flat panel test results, or average film thickness requirements. Quality is then evaluated after curing based on gloss, roughness, or orange peel grade. However, process parameters obtained from flat panel tests are insufficient to fully reflect the combined effects of the bumper's complex curvature, spray run overlap, the timing of area spraying completion, and the changes in clear coat viscosity during flash-off and curing on texture attenuation. This can easily lead to situations where the film thickness meets requirements but the cured texture is inconsistent, resulting in poor spraying performance. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method and system for controlling the spraying of clear coat on automotive bumper skin, aiming to solve the technical problem of poor spraying effect in the prior art.

[0005] To achieve the above objectives, in a first aspect, the present invention provides: a method for controlling the spraying of clear coat on an automotive bumper skin, comprising the following steps: Acquire the coating surface data of the vehicle body exterior covering adjacent to the bumper skin and the curved surface data of the bumper skin, and determine the target texture features of different curved surface areas of the bumper skin at multiple surface spatial scales; Clear coat is applied to the calibration object corresponding to the bumper skin. The texture features of the clear coat in the wet film state and the cured state are obtained respectively. Based on the texture change between the two states, the texture attenuation relationship under different surface spatial scales is determined. Based on the candidate spraying process parameters, the expected wet film morphology data of each curved area of ​​the bumper skin is determined. Initial texture features are extracted from the expected wet film morphology data, and the corresponding cured texture features are predicted based on the texture attenuation relationship. Based on the deviation between the cured texture features and the corresponding target texture features, and in conjunction with the film-forming constraints of the clear coat, the target spraying process parameters are determined from the candidate spraying process parameters, so as to perform clear coat spraying on the bumper skin according to the target spraying process parameters.

[0006] According to one aspect of the above technical solution, the steps for identifying changes in the output of cold and heat sources specifically include: The specific steps for determining the target texture features of different curved areas of the bumper skin at multiple surface spatial scales include: Based on the assembly position relationship between the bumper skin and the adjacent body exterior panels in the reference vehicle body, an appearance reference area corresponding to each curved surface area of ​​the bumper skin is determined on the adjacent body exterior panels. Acquire reflective surface topography data of each appearance reference area along a preset observation direction, and establish local coordinates extending along the surface of the bumper skin based on the surface data of the bumper skin, and transform the reflective surface topography data to the local coordinates of the corresponding surface area. Remove the matrix surface shape from the reflective surface topography data, and extract the texture amplitude within multiple preset surface wavelength ranges. Arrange the texture amplitudes in order of surface wavelength to form the target texture spectrum of the corresponding surface region.

[0007] According to one aspect of the above technical solution, the steps for obtaining the reflective surface morphology data of each appearance reference area specifically include: A display device sequentially displays sinusoidal fringes with phase shifts, and an imaging device acquires fringes images reflected from the surface of the coating being tested, such that the image intensity of the p-th sampling point under the j-th phase shift satisfies: ; In the formula, For image intensity, The average background intensity, For striped tones, To wrap the phase, This represents the total number of fringe phase shifts. Here, j is the sampling point number, and j is the phase offset number; The wrap phase of the p-th sampling point is determined according to the following formula: ; The wrapped phase is unfolded, and according to the pre-calibrated positional relationship between the display device, the imaging device and the surface of the coating being tested, the unfolded phase is converted into the surface slope of the corresponding sampling point. The surface slope is then integraled to obtain the height data of the surface of the coating being tested.

[0008] According to one aspect of the above technical solution, the step of extracting texture amplitude values ​​within multiple preset surface wavelength ranges specifically includes: Fit the base surface in the local coordinates of the u-th surface region, and obtain the surface residual after removing the shape of the base surface according to the following formula: ; In the formula, To remove surface residuals after the base surface shape is removed, The height of the varnish surface. The height of the fitted matrix surface, The coordinates of the local curved surface in the spraying area; A two-dimensional spectral transform with area normalization is performed on the surface residual, and the first spectral value is determined according to the following formula. The texture amplitude of each texture band is calculated, and texture bands with texture amplitudes below the measured noise threshold are excluded from the texture spectrum. ; ; In the formula, For texture amplitude, For the first The spatial frequency range corresponding to each texture band. The frequency domain area is the area within the spatial frequency range. Let be the spatial angular frequency vector, and , and These represent the spatial angular frequency components along the local coordinate directions ξ and χ, respectively. Represents the squared modulus of the complex amplitude of the spectrum. The two-dimensional spectral value is obtained by normalizing the surface residual of the u-th surface region at the spatial angular frequency ω. Represents a spatial angular frequency element. Let u be the spatial sampling range of the u-th surface region. This represents the actual surface area. For the u-th surface region in local coordinates The surface residual after removing the shape of the substrate surface. This represents a local surface coordinate element, where i is the imaginary unit.

[0009] According to one aspect of the above technical solution, the steps for determining the texture attenuation relationship at different surface spatial scales specifically include: Select a calibration object that has the same base material as the bumper skin and whose surface curvature is within a preset curvature range of the corresponding curved surface area, and apply clear coat to the calibration object under preset spraying conditions; Surface height data of the calibration object were acquired before the clear varnish entered the flash-off stage and after curing was completed, and the u-th curved surface region was extracted in the first stage. The wet film texture amplitude and the cured texture amplitude under each texture band must satisfy the following: ; In the formula, , These are the cured texture amplitude and the wet film texture amplitude, respectively. To calibrate the leveling migration, For the first The non-zero values ​​of each texture band represent the spatial wavenumber; The calibration leveling migration of the u-th surface region is determined according to the following formula: ; In the formula, L represents the total number of effective texture bands; When the fitting residual between the texture amplitude obtained based on the calibrated leveling migration amount and the measured solidified texture amplitude exceeds the preset residual threshold, the range of the corresponding curved surface region is reduced and the calibrated leveling migration amount is re-determined.

[0010] According to one aspect of the above technical solution, the steps for determining the expected wet film morphology data of each curved surface region of the bumper skin include: Obtain the normalized spray pattern distribution of the spray gun under different spraying distances and incident angles. Based on the candidate spray gun trajectory, clear coat flow rate, and spray gun moving speed, determine the expected wet film thickness formed by the overlapping of multiple spray lines at the p-th surface sampling point according to the following formula: ; In the formula, Let r be the wet film thickness at the p-th sampling point, and let r and M be the spray lane number and the total number of spray lanes, respectively. Let be the clear coat transfer efficiency of the r-th spray pass. Let be the volumetric flow rate of the clear coat for the r-th spray pass. Let be the spray gun moving speed of the r-th spray lane. Let be the lateral distance of the surface from the sampling point to the center line of the r-th spray duct. The spraying distance from the spray gun to the sampling point. The angle between the spray gun axis and the normal of the sampling point surface. The normalized lateral deposition distribution of the r-th spray duct at the corresponding spray distance and incident angle; The predicted wet film thickness at each surface sampling point is used to construct the predicted wet film morphology data, and the average wet film thickness and predicted cured film thickness of the u-th surface region are determined according to the following formula: ; ; In the formula, The candidate average wet film thickness, To predict the thickness of the cured film, This represents the volume fraction of solids in the varnish. This represents the surface area weight corresponding to the p-th surface sampling point.

[0011] According to one aspect of the above technical solution, the step of predicting the corresponding solidified texture features based on the texture attenuation relationship specifically includes: Remove the regional average thickness and low-frequency thickness variation trend from the expected wet film morphology data, and extract the initial texture amplitude of the u-th surface region according to each texture band; When the varnish material and spraying environment are within the corresponding calibration range, the calibrated leveling migration amount is converted according to the average wet film thickness and effective leveling duration using the following formula: ; ; ; In the formula, Let be the leveling migration amount of the u-th curved surface region under the candidate spraying conditions. To calibrate the average wet film thickness, the superscript 'c' indicates the calibration spraying conditions. To calibrate the leveling migration under spraying conditions, and The average wet film thicknesses are those under candidate spraying conditions and those under calibration spraying conditions, respectively. The effective leveling time from the completion of spraying the clear coat to the point where the varnish essentially stops flowing in the u-th curved surface region. To calibrate the effective leveling time for the corresponding curved surface area under spraying conditions, and These are the integrals of the flowability under candidate spraying conditions and calibration spraying conditions, respectively. Let dt represent the equivalent apparent viscosity of the clear coat in the u-th curved region at time t, where t represents the time variable calculated from the time the corresponding curved region is sprayed, and dt is a time infinitesimal element. The following formula predicts the u-th surface region in the... Solidified texture amplitude under each texture band: ; In the formula, To predict the amplitude of the cured texture, The initial texture amplitude is formed by the candidate spraying parameters.

[0012] According to one aspect of the above technical solution, the steps for determining the target spraying process parameters specifically include: The candidate spraying process parameters are composed of the spray lane spacing, spray gun posture, clear coat flow rate of each spray lane, and spray gun movement speed. The target spraying process parameters are selected according to the following formula: ; In the formula, This represents the set of candidate spraying process parameters. Let C represent the set of target spraying process parameters, where C represents the feasible set of candidate parameters that satisfy the operation of the spraying equipment, u represents the surface region number, and U represents the total number of surface regions. This represents the target solidified texture amplitude for the corresponding curved surface region and texture band. Indicates the first The allowable target logarithmic amplitude deviation for each texture band.

[0013] According to one aspect of the above technical solution, the steps of applying clear coat according to the target spraying process parameters specifically include: Control the spray gun to move along the target spray gun trajectory determined by the target spraying process parameters, and perform clear varnish spraying according to the target clear varnish flow rate and target spray gun moving speed corresponding to each spraying pass; After completing the corresponding spraying passes in each curved area and before the overall spraying of the bumper skin is finished, obtain the actual wet film surface data of the corresponding curved area and determine the actual wet film thickness. When the actual wet film thickness exceeds the allowable wet film thickness range determined by the cured film thickness constraint and the sagging limit thickness, no reverse spraying is performed on the already sprayed curved area, and the clear varnish flow rate or spray gun movement speed of the adjacent spraying lanes that have not yet been executed is adjusted according to the wet film thickness deviation. After all spraying passes are completed, the bumper skin is controlled to enter the curing process according to the target curing process entry time. After the clear coat has cured, the actual cured texture amplitude of each curved area is obtained, and the actual cured texture amplitude is compared with the corresponding target cured texture amplitude to obtain the clear coat spraying quality evaluation result.

[0014] On the other hand, the present invention also provides a system for implementing the automotive bumper skin clear coat spraying control method described in the above technical solution, comprising: The data module acquires the coating surface data of the body exterior covering adjacent to the bumper skin and the curved surface data of the bumper skin, and determines the target texture features of different curved areas of the bumper skin at multiple surface spatial scales. The calibration module is used to apply clear coat to the calibration object corresponding to the bumper skin, obtain the texture features of the clear coat when it is in a wet film state and a cured state, and determine the texture attenuation relationship at different surface spatial scales based on the texture change between the two states. The prediction module is used to determine the expected wet film morphology data of each curved area of ​​the bumper skin based on the candidate spraying process parameters, extract the initial texture features from the expected wet film morphology data, and predict the corresponding cured texture features based on the texture attenuation relationship. The target module is used to determine the target spraying process parameters from the candidate spraying process parameters based on the deviation between the cured texture features and the corresponding target texture features, and in combination with the film-forming constraints of the clear coat coating, so as to perform clear coat spraying on the bumper skin according to the target spraying process parameters.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: By determining the corresponding appearance reference areas for different curved surface areas of the bumper skin according to the assembly position relationship between the bumper skin and adjacent body panels, and extracting target texture features from multiple surface wavelength ranges, the spraying control target is transformed from a single film thickness or roughness index into a multi-scale texture target corresponding to the actual adjacent body panels; by obtaining wet film texture and cured texture on a calibration object with matching curvature and coating system, and establishing the attenuation relationship of different texture bands, the leveling effect of the clear coat during flash-drying and curing processes can be reflected; by combining the spray gun spray width distribution, candidate spraying parameters and bumper skin surface data, the wet film morphology is predicted, and based on the average wet film thickness and the completion of regional spraying... The method of predicting cured texture by engraving, unifying the curing entry time, and clear coat flowability improves the targeting of complex surface texture prediction. Among the candidate parameters that meet the operating conditions of the spraying equipment, the requirements of cured film thickness, and the limitation of sagging, the target spraying process parameters are determined based on the maximum deviation of each surface area and each texture band. This can avoid improving only a local area and causing obvious appearance differences in other areas. At the same time, the method adjusts the unexecuted spraying lanes according to the actual wet film thickness during the spraying process and avoids back-spraying of completed areas. This helps to reduce the risk of local over-thickness, sagging, and texture abrupt changes, thereby improving the appearance coordination between the bumper skin and adjacent body exterior parts and the batch spraying consistency, and reducing the material consumption and process debugging time caused by repeated test spraying. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the method for controlling the spraying of clear coat on automotive bumper skin in the first embodiment of the present invention. Figure 2 This is a structural block diagram of the automotive bumper skin clear coat spraying control system in the second embodiment of the present invention; The following detailed description, in conjunction with the accompanying drawings, will further illustrate the present invention. Detailed Implementation

[0017] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Several embodiments of the invention are illustrated in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0019] Example 1 Please see Figure 1 The figure shows a flowchart of the method for controlling the spraying of clear coat on a car bumper skin according to the first embodiment of the present invention. As shown in the figure, the method includes the following steps: Step S100: Obtain the coating surface data of the vehicle body exterior covering adjacent to the bumper skin and the curved surface data of the bumper skin, and determine the target texture features of different curved surface areas of the bumper skin at multiple surface spatial scales. In this embodiment, the curved surface data can be obtained from the three-dimensional design model of the bumper skin, or it can be obtained by scanning the actual bumper skin using a three-dimensional scanning device. Based on the curvature change, the surface normal change, the assembly position, and the visible area, the bumper skin is divided into multiple curved surface areas, and each curved surface area is numbered according to a preset order, with the u-th curved surface area denoted by u.

[0020] For example, the bumper skin can be divided into a central main area, two side transition areas, corner areas, and edge areas adjacent to the fenders or side panels. The area boundaries are preferably set at locations with significant curvature changes or at visually distinct zones, ensuring relatively consistent curvature and clear coat leveling characteristics within the same curved surface area.

[0021] A reference vehicle body that has been assembled and meets appearance quality requirements is selected. Based on the assembly position relationship between the bumper skin and adjacent exterior body panels in the reference vehicle body, appearance reference areas corresponding to each curved surface area of ​​the bumper skin are determined on the adjacent exterior body panels. For the front bumper skin, the adjacent exterior body panel may include a fender or an engine hood; for the rear bumper skin, the adjacent exterior body panel may include a rear side panel or a trunk lid. The correspondence can be determined based on the assembly seam position, surface normal, and preset viewing direction, rather than simply selecting reference areas according to spatial distance.

[0022] Acquire reflective surface morphology data for each exterior reference area along a preset observation direction. The preset observation direction can be the standard observation direction specified in the vehicle exterior inspection station, or it can be the direction consistent with the actual visible direction of the adjacent vehicle body exterior panels.

[0023] In one implementation, phase-measured deflection is used to acquire the topographic data of the reflective surface. A display device sequentially displays sinusoidal fringes with different phase shifts, and an imaging device acquires the fringes image after reflection from the surface of the coating under test. The image intensity of the p-th sampling point under the j-th phase shift satisfies: ; In the formula, Let p be the image intensity of the p-th sampling point under the j-th phase shift. The average background intensity, For striped tones, To wrap the phase, This represents the total number of fringe phase shifts. Here, j is the sampling point number, and j is the phase shift number; the total number of fringe phase shifts J is an integer not less than 3. For example, when using a four-step phase shift, J=4, and the display device sequentially displays sinusoidal fringes with phase shifts of 0, π / 2, π, and 3π / 2.

[0024] The wrap phase of the p-th sampling point is determined according to the following formula: Where, atan2 represents the two-parameter arctangent operation that determines the quadrant of the phase based on the signs of the two input quantities. The resulting wrapped phase is then expanded to eliminate the 2π phase jump that occurs between adjacent periods.

[0025] Based on the pre-calibrated positional relationship between the display device, imaging device, and the surface of the coating under test, the unfolded phase is converted into the surface slope along two local coordinate directions at the corresponding sampling points. The height data of the coating surface is obtained by performing two-dimensional integral reconstruction of the surface slope field. Two-dimensional integral reconstruction can employ a least-squares-based integration method to reduce the impact of local measurement noise and the non-perfect integrability of the slope field on the height reconstruction results.

[0026] Based on the surface data of the bumper skin, local coordinates extending along the surface are established in each surface region. These local coordinates include coordinate axes set along two tangential directions of the surface and a height direction set along the normal direction of the surface. Through coordinate transformation, the reflective surface topography data of the exterior reference area is converted to the local coordinates of the corresponding surface region, enabling comparison between the exterior reference area and the corresponding bumper skin surface region at the same local spatial scale.

[0027] Fit the base surface in the local coordinates of the u-th surface region, and obtain the surface residual after removing the shape of the base surface according to the following formula: ; In the formula, To remove surface residuals after the base surface shape is removed, The height of the varnish surface. The height of the fitted matrix surface, Let these be the local surface coordinates of the spraying area. , These represent the two tangential coordinates of the local surface. The base surface can be fitted using a polynomial surface, spline surface, or a theoretical surface obtained from the 3D design model of the bumper skin. The spatial scale corresponding to the fitting is larger than the maximum texture wavelength to be analyzed, thus avoiding the simultaneous removal of long-wavelength textures that need to be retained when removing the shape of the base surface.

[0028] A two-dimensional spectral transform with area normalization is performed on the surface residual, and the first spectral value is determined according to the following formula. The texture amplitude of each texture band is calculated, and texture bands with texture amplitudes below the measured noise threshold are excluded from the texture spectrum. ; ; In the formula, For texture amplitude, For the first The spatial frequency range corresponding to each texture band. The frequency domain area is the area within the spatial frequency range. Let be the spatial angular frequency vector, and , and These represent the spatial angular frequency components along the local coordinate directions ξ and χ, respectively. Represents the squared modulus of the complex amplitude of the spectrum. The surface residual of the u-th surface region at the spatial angular frequency The normalized two-dimensional spectrum value, Represents a spatial angular frequency element. Let u be the spatial sampling range of the u-th surface region. This represents the actual surface area. For the u-th surface region in local coordinates The surface residual after removing the shape of the substrate surface. This represents a local surface coordinate element, where i is the imaginary unit.

[0029] Each texture band can be continuously divided according to the surface wavelength. For a surface wavelength range of [λ] ,min,λ The texture band [max] has a corresponding spatial angular frequency range that can be determined based on the reciprocal relationship between the spatial angular frequency and the surface wavelength. The representative spatial wavenumber k of each texture band The center space wavenumber or energy-weighted space wavenumber of this band can be used, and k Not zero.

[0030] Texture bands with texture amplitudes below the measurement noise threshold are excluded, and the texture amplitudes of the remaining texture bands are arranged in order of surface wavelength to form the target texture spectrum for the corresponding curved surface region.

[0031] Step S200: Apply clear coat to the calibration object corresponding to the bumper skin, and obtain the texture features of the clear coat in the wet film state and the cured state respectively. Based on the texture change between the two states, determine the texture attenuation relationship under different surface spatial scales.

[0032] Specifically, a calibration object is selected that has the same base material as the bumper skin and whose surface curvature is within a preset curvature range of the corresponding curved surface area. The calibration object can be a calibration test plate made according to a local curved surface of the bumper skin, or a sample manufactured in the same batch as the bumper skin to be painted. Clear coat is applied to the calibration object under preset painting conditions. The preset painting conditions include at least one or more of the following: spraying distance, spray gun incident angle, clear coat flow rate, spray gun moving speed, spray lane spacing, ambient temperature, ambient humidity, and curing temperature.

[0033] Before the clear coat is applied and enters the flash-drying stage, the surface height data of the clear coat wet film is obtained using a non-contact surface morphology measurement method; after curing, the surface height data of the cured film is obtained within the same local coordinates and sampling range.

[0034] Based on the aforementioned spectrum extraction method, the u-th surface region is determined in the... The wet film texture amplitude and the cured texture amplitude under each texture band satisfy the following: ; In the formula, , These are the cured texture amplitude and the wet film texture amplitude, respectively. To calibrate the leveling migration, For the first The non-zero values ​​of each texture band represent the spatial wavenumber; The texture attenuation relationship shows that, under the same leveling migration, short-wave textures, representing larger spatial wavenumbers, attenuate faster, while long-wave textures, representing smaller spatial wavenumbers, are retained to a higher degree. Therefore, by calibrating multiple texture bands together, it is possible to avoid describing the varnish leveling process using only a single roughness parameter.

[0035] The calibration leveling migration of the u-th surface region is determined according to the following formula: ; In the formula, L represents the total number of effective texture bands; max{0, The} symbol indicates that the calibration leveling migration is limited to zero when the calculation result is less than zero.

[0036] Based on the obtained calibration leveling migration, the solidified texture amplitude of each effective texture band is recalculated, and the calculation results are compared with the measured solidified texture amplitude. When the fitting residual does not exceed the preset residual threshold, the corresponding calibration leveling migration is retained.

[0037] When the fitting residual exceeds the preset residual threshold, it indicates that there may be parts with large curvature changes, different flow leveling durations, or different thermal environments within the same surface region. Therefore, the range of the corresponding surface region is reduced, and the calibration flow leveling migration of each reduced region is recalculated until the fitting residual meets the requirements.

[0038] Step S300: Determine the expected wet film morphology data of each curved area of ​​the bumper skin according to the candidate spraying process parameters, extract the initial texture features from the expected wet film morphology data, and predict the corresponding cured texture features according to the texture attenuation relationship.

[0039] A set of surface sampling points is established based on the surface data of the bumper skin. Each surface sampling point has a corresponding spatial position, surface normal, and surface area weight. The normalized spray pattern distribution of the spray gun under different spraying distances and different incident angles is obtained.

[0040] For each set of candidate spraying process parameters, based on the candidate spray gun trajectory, clear coat flow rate, and spray gun movement speed, the expected wet film thickness formed by the overlapping of multiple spray lines at the p-th surface sampling point is calculated using the following formula: ; In the formula, Let r be the wet film thickness at the p-th sampling point, and let r and M be the spray lane number and the total number of spray lanes, respectively. Let be the clear coat transfer efficiency of the r-th spray pass. Let be the volumetric flow rate of the clear coat for the r-th spray pass. Let be the spray gun moving speed of the r-th spray lane. Let be the lateral distance of the surface from the sampling point to the center line of the r-th spray duct. The spraying distance from the spray gun to the sampling point. The angle between the spray gun axis and the normal of the sampling point surface. Let represent the normalized lateral deposition distribution of the r-th spray path at the corresponding spray distance and incident angle. The clear coat transfer efficiency can be determined based on the spray gun model, atomization parameters, spray distance, incident angle, and historical calibration results. Since the amount of sprayed deposits is positively correlated with the clear coat flow rate and negatively correlated with the spray gun movement speed, the ratio of clear coat flow rate to spray gun movement speed is used to characterize the amount of clear coat supplied per unit trajectory length.

[0041] The expected wet film thicknesses of all surface sampling points are arranged according to their positions on the bumper skin surface to form expected wet film morphology data. The average wet film thickness of the u-th surface region is determined by the following formula: ; The candidate average wet film thickness, The surface area weight corresponding to the p-th surface sampling point; The predicted cured film thickness is determined by the following formula: ; To predict the thickness of the cured film, This represents the volume fraction of solids in the varnish. The average wet film thickness and low-frequency thickness variation trend of the u-th surface region are removed from the expected wet film morphology data. The initial texture amplitude of the surface region under each texture band is extracted using the same texture band division method as the target texture spectrum.

[0042] When the varnish material and spraying environment are within the calibration range, the calibration leveling migration is converted to the leveling migration under the candidate spraying conditions based on the candidate average wet film thickness and effective leveling duration: ; ; ; In the formula, Let be the leveling migration amount of the u-th curved surface region under the candidate spraying conditions. To calibrate the average wet film thickness, the superscript 'c' indicates the calibration spraying conditions. To calibrate the leveling migration under spraying conditions, and The average wet film thicknesses are those under candidate spraying conditions and those under calibration spraying conditions, respectively. The effective leveling time from the completion of spraying the clear coat to the point where the varnish essentially stops flowing in the u-th curved surface region. To calibrate the effective leveling time for the corresponding curved surface area under spraying conditions, and These are the integrals of the flowability under candidate spraying conditions and calibration spraying conditions, respectively. Let dt represent the equivalent apparent viscosity of the clear coat in the u-th curved region at time t, where t represents the time variable calculated from the time the corresponding curved region is sprayed, and dt is a time infinitesimal element. The equivalent apparent viscosity change process of varnish can be obtained by looking up tables or interpolation based on the pre-calibrated viscosity-temperature-time data of the varnish material, as well as the spraying environment temperature, flash-off temperature, and curing temperature rise process.

[0043] The following formula predicts the u-th surface region in the... Solidified texture amplitude under each texture band: ; In the formula, To predict the amplitude of the cured texture, The initial texture amplitude is formed by the candidate spraying parameters.

[0044] Step S400: Based on the deviation between the cured texture feature and the corresponding target texture feature, and in conjunction with the film-forming constraint of the clear coat coating, determine the target spraying process parameters from the candidate spraying process parameters, and apply clear coat to the bumper skin according to the target spraying process parameters.

[0045] Candidate spraying process parameters include spray lane spacing, spray gun posture, clear coat flow rate for each spray lane, and spray gun movement speed. Spray gun posture includes the spatial position of the spray gun relative to the bumper skin surface and the direction of the spray gun axis.

[0046] The candidate spraying process parameters achievable by the spraying equipment are grouped into a feasible set C of candidate parameters. The parameters in the feasible set of candidate parameters satisfy the allowable flow rate range of the spray gun, the allowable moving speed of the spray gun, the robot's movement range, the spraying distance range, the incident angle range, and the overlap requirements of adjacent spray lines.

[0047] Candidate parameters are further screened by considering the film-forming constraints of the clear coat coating. Film-forming constraints include at least cured film thickness constraints and sagging limit thickness. For the u-th curved surface region, the predicted cured film thickness should be within the preset cured film thickness range; for the curved surface sampling point, the predicted wet film thickness should not exceed the sagging limit thickness under the corresponding curved surface tilt state. The sagging limit thickness can be obtained by conducting clear coat spraying tests at different curved surface tilt angles, and establishing a correspondence between the curved surface tilt angle and the upper limit of the allowable wet film thickness. For curved surface regions that are close to vertical, a smaller upper limit of the allowable wet film thickness can be used.

[0048] The target spraying process parameters are selected from the feasible set of candidate parameters according to the following formula: ; In the formula, This represents the set of candidate spraying process parameters. Let C represent the set of target spraying process parameters, where C represents the feasible set of candidate parameters that satisfy the operation of the spraying equipment, u represents the surface region number, and U represents the total number of surface regions. This represents the target solidified texture amplitude for the corresponding curved surface region and texture band. Indicates the first The allowable target logarithmic amplitude deviation for each texture band.

[0049] The objective function described above uses the maximum normalized texture deviation in each surface region and each texture band as the evaluation metric, so that the final determined spraying process parameters will not only improve the matching degree of local areas or individual texture bands, but also cause obvious appearance differences in other areas.

[0050] Candidate spraying process parameters can be solved through discrete traversal, progressively narrowing the search range, or numerical optimization. First, candidate parameters that do not meet equipment operating conditions, cured film thickness constraints, or sagging limitations are eliminated. Then, the objective function value is calculated for the remaining candidate parameters, and the parameter with the smallest objective function value is selected as the target spraying process parameter.

[0051] The target spray gun trajectory is generated based on the target spray lane spacing, target spray gun posture, and bumper skin surface data. The spray gun is controlled to move along the target spray gun trajectory, and clear coat is applied according to the target clear coat flow rate and target spray gun movement speed corresponding to each spray lane.

[0052] After the corresponding spraying passes are completed in each curved area, and before the overall spraying of the bumper skin is finished, the actual wet film surface data of the corresponding curved area is obtained through a non-contact wet film detection device, and the actual wet film thickness is determined accordingly.

[0053] The wet film detection device can be fixedly installed at the spraying station or mounted on a detection mechanism that moves in coordination with the spraying robot. The detection timing is set within the time period after the spraying run of the corresponding curved surface area has been completed, but before the spray gun has executed the subsequent adjacent spraying run, so as to use the detection results to adjust the unexecuted spraying run.

[0054] The allowable wet film thickness range is determined based on the curing film thickness constraint and the sagging thickness limit. Let the lower and upper limits of the curing film thickness be D, respectively. min and D max The lower and upper limits of the wet film thickness, calculated based on the solids volume fraction of the varnish, are D, respectively. min / α and D max / α. The maximum allowable wet film thickness does not exceed the sag limit thickness of the corresponding curved surface region.

[0055] When the actual wet film thickness is within the allowable wet film thickness range, continue to execute subsequent spray passes according to the target spraying process parameters. When the actual wet film thickness is lower than the lower limit of the allowable wet film thickness range, appropriately increase the clear coat flow rate of the adjacent spray passes that have not yet been executed or decrease the spray gun movement speed; when the actual wet film thickness is higher than the upper limit of the allowable wet film thickness range, appropriately decrease the clear coat flow rate of the adjacent spray passes that have not yet been executed or increase the spray gun movement speed.

[0056] After adjustment, the amount of deposition on adjacent curved areas by the unexecuted spray lines is predicted again based on the spray pattern overlap relationship, and the adjusted parameters are ensured to remain within the operating range of the spraying equipment and the drip limit.

[0057] Do not control the spray gun to return to the already sprayed curved area for re-spraying. This avoids changing the surface texture, effective flash-off time and leveling state of the already sprayed area, and also avoids local repeated spraying that could cause the wet film thickness to exceed the sagging limit.

[0058] After all spraying passes are completed, the bumper skin is controlled to enter the curing process according to the target curing process entry time corresponding to the target spraying process parameters, and the clear coat is cured according to the preset curing temperature process.

[0059] After the clear coat has cured, the actual cured surface height data of each curved area is obtained using the same surface topography measurement method as the target texture measurement. The substrate surface shape is removed, and the actual cured texture amplitude of each effective texture band is extracted. The actual cured texture amplitude is compared with the corresponding target cured texture amplitude to obtain the clear coat spraying quality evaluation result.

[0060] Preferably, in some application scenarios of this embodiment, the maximum normalized logarithmic amplitude deviation of each curved surface region and each texture band can be used as a quality evaluation index. When the actual deviation of each texture band does not exceed the corresponding allowable target logarithmic amplitude deviation, it is determined that the clear coat texture of the bumper skin meets the appearance matching requirements with the adjacent vehicle body exterior covering; otherwise, the curved surface regions and texture bands that do not meet the requirements are recorded for quality traceability.

[0061] In summary, the automotive bumper skin clear coat spraying control method in the above embodiments of the present invention determines corresponding appearance reference areas for different curved surface areas of the bumper skin based on the assembly position relationship between the bumper skin and adjacent body panels, and extracts target texture features from multiple surface wavelength ranges, transforming the spraying control target from a single film thickness or roughness index into a multi-scale texture target corresponding to the actual adjacent body panels; by obtaining wet film texture and cured texture on a calibration object with matching curvature and coating system, and establishing the attenuation relationship of different texture bands, it can reflect the leveling effect of the clear coat during flash-drying and curing processes; by combining the spray gun spray width distribution, candidate spraying parameters, and bumper skin surface data, the wet film morphology is predicted, and based on the average wet film thickness, area... Predicting cured texture based on the completion time of domain spraying, the unified curing entry time, and the flowability of clear coat improves the targeting of complex surface texture prediction. Among candidate parameters that meet the operating conditions of spraying equipment, cured film thickness requirements, and sagging limitations, the target spraying process parameters are determined based on the maximum deviation of each surface region and each texture band. This avoids improving only local areas while causing significant appearance differences in other areas. At the same time, adjusting unexecuted spray passes according to the actual wet film thickness during the spraying process and avoiding back-spraying of completed areas helps reduce the risk of local over-thickness, sagging, and abrupt texture changes. This improves the appearance coordination between the bumper skin and adjacent body panels and the consistency of batch spraying, while reducing material consumption and process debugging time caused by repeated test spraying.

[0062] Example 2 like Figure 2 As shown, the second embodiment of the present invention provides a clear coat spraying control system for automotive bumper skin, comprising: Data module 100 acquires the coating surface data of the vehicle body exterior covering adjacent to the bumper skin and the curved surface data of the bumper skin, and determines the target texture features of different curved surface areas of the bumper skin at multiple surface spatial scales. The calibration module 200 is used to apply clear coat to the calibration object corresponding to the bumper skin, obtain the texture features of the clear coat when it is in a wet film state and a cured state, and determine the texture attenuation relationship at different surface spatial scales based on the texture change between the two states. The prediction module 300 is used to determine the expected wet film morphology data of each curved surface area of ​​the bumper skin according to the candidate spraying process parameters, extract the initial texture features from the expected wet film morphology data, and predict the corresponding cured texture features according to the texture attenuation relationship. The target module 400 is used to determine the target spraying process parameters from the candidate spraying process parameters based on the deviation between the cured texture features and the corresponding target texture features, and in combination with the film-forming constraints of the clear coat coating, so as to perform clear coat spraying on the bumper skin according to the target spraying process parameters.

[0063] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for controlling the spraying of clear coat on automotive bumper skin, characterized in that, Includes the following steps: Acquire the coating surface data of the vehicle body exterior covering adjacent to the bumper skin and the curved surface data of the bumper skin, and determine the target texture features of different curved surface areas of the bumper skin at multiple surface spatial scales; Clear coat is applied to the calibration object corresponding to the bumper skin. The texture features of the clear coat in the wet film state and the cured state are obtained respectively. Based on the texture change between the two states, the texture attenuation relationship under different surface spatial scales is determined. Based on the candidate spraying process parameters, the expected wet film morphology data of each curved area of ​​the bumper skin is determined. Initial texture features are extracted from the expected wet film morphology data, and the corresponding cured texture features are predicted based on the texture attenuation relationship. Based on the deviation between the cured texture features and the corresponding target texture features, and in conjunction with the film-forming constraints of the clear coat, the target spraying process parameters are determined from the candidate spraying process parameters, so as to perform clear coat spraying on the bumper skin according to the target spraying process parameters.

2. The method for controlling the spraying of clear coat on automotive bumper skin according to claim 1, characterized in that, The specific steps for determining the target texture features of different curved areas of the bumper skin at multiple surface spatial scales include: Based on the assembly position relationship between the bumper skin and the adjacent body exterior panels in the reference vehicle body, an appearance reference area corresponding to each curved surface area of ​​the bumper skin is determined on the adjacent body exterior panels. Acquire reflective surface topography data of each appearance reference area along a preset observation direction, and establish local coordinates extending along the surface of the bumper skin based on the surface data of the bumper skin, and transform the reflective surface topography data to the local coordinates of the corresponding surface area. Remove the matrix surface shape from the reflective surface topography data, and extract the texture amplitude within multiple preset surface wavelength ranges. Arrange the texture amplitudes in order of surface wavelength to form the target texture spectrum of the corresponding surface region.

3. The method for controlling the spraying of clear coat on automotive bumper skin according to claim 2, characterized in that, The specific steps for obtaining the reflective surface topography data of each appearance reference area include: A display device sequentially displays sinusoidal fringes with phase shifts, and an imaging device acquires fringes images reflected from the surface of the coating being tested, such that the image intensity of the p-th sampling point under the j-th phase shift satisfies: ； In the formula, For image intensity, The average background intensity, For striped tones, To wrap the phase, This represents the total number of fringe phase shifts. Here, j is the sampling point number, and j is the phase offset number; The wrap phase of the p-th sampling point is determined according to the following formula: ； The wrapped phase is unfolded, and according to the pre-calibrated positional relationship between the display device, the imaging device and the surface of the coating being tested, the unfolded phase is converted into the surface slope of the corresponding sampling point. The surface slope is then integraled to obtain the height data of the surface of the coating being tested.

4. The method for controlling the spraying of clear coat on automotive bumper skin according to claim 3, characterized in that, The specific steps for extracting texture amplitude values ​​within multiple preset surface wavelength ranges include: Fit the base surface in the local coordinates of the u-th surface region, and obtain the surface residual after removing the shape of the base surface according to the following formula: ； In the formula, To remove surface residuals after the base surface shape is removed, The height of the varnish surface. The height of the fitted matrix surface, The coordinates of the local curved surface in the spraying area; A two-dimensional spectral transform with area normalization is performed on the surface residual, and the first spectral value is determined according to the following formula. The texture amplitude of each texture band is calculated, and texture bands with texture amplitudes below the measured noise threshold are excluded from the texture spectrum. ； ； In the formula, For texture amplitude, For the first The spatial frequency range corresponding to each texture band. The frequency domain area is the area within the spatial frequency range. Let be the spatial angular frequency vector, and , and These represent the spatial angular frequency components along the local coordinate directions ξ and χ, respectively. Represents the squared modulus of the complex amplitude of the spectrum. The surface residual of the u-th surface region at the spatial angular frequency The normalized two-dimensional spectrum value, Represents a spatial angular frequency element. Let u be the spatial sampling range of the u-th surface region. This represents the actual surface area. For the u-th surface region in local coordinates The surface residual after removing the shape of the substrate surface. This represents a local surface coordinate element, where i is the imaginary unit.

5. The method for controlling the spraying of clear coat on automotive bumper skin according to claim 4, characterized in that, The specific steps for determining the texture attenuation relationship at different surface spatial scales include: Select a calibration object that has the same base material as the bumper skin and whose surface curvature is within a preset curvature range of the corresponding curved surface area, and apply clear coat to the calibration object under preset spraying conditions; Surface height data of the calibration object were acquired before the clear varnish entered the flash-off stage and after curing was completed, and the u-th curved surface region was extracted at the 1st... The wet film texture amplitude and the cured texture amplitude under each texture band must satisfy the following: ； In the formula, , These are the cured texture amplitude and the wet film texture amplitude, respectively. To calibrate the leveling migration, For the first The non-zero values ​​of each texture band represent the spatial wavenumber; The calibration leveling migration of the u-th surface region is determined according to the following formula: ； In the formula, L represents the total number of effective texture bands; When the fitting residual between the texture amplitude obtained based on the calibrated leveling migration amount and the measured solidified texture amplitude exceeds the preset residual threshold, the range of the corresponding curved surface region is reduced and the calibrated leveling migration amount is re-determined.

6. The method for controlling the spraying of clear coat on automotive bumper skin according to claim 5, characterized in that, The steps for determining the expected wet film morphology data for each curved area of ​​the bumper skin include: Obtain the normalized spray pattern distribution of the spray gun under different spraying distances and incident angles. Based on the candidate spray gun trajectory, clear coat flow rate, and spray gun moving speed, determine the expected wet film thickness formed by the overlapping of multiple spray lines at the p-th surface sampling point according to the following formula: ； In the formula, Let r be the wet film thickness at the p-th sampling point, and let r and M be the spray lane number and the total number of spray lanes, respectively. Let be the clear coat transfer efficiency of the r-th spray pass. Let be the volumetric flow rate of the clear coat for the r-th spray pass. Let be the spray gun moving speed of the r-th spray lane. Let be the lateral distance of the surface from the sampling point to the center line of the r-th spray duct. The spraying distance from the spray gun to the sampling point. The angle between the spray gun axis and the normal of the sampling point surface. The normalized lateral deposition distribution of the r-th spray duct at the corresponding spray distance and incident angle; The predicted wet film thickness at each surface sampling point is used to construct the predicted wet film morphology data, and the average wet film thickness and predicted cured film thickness of the u-th surface region are determined according to the following formula: ； ； In the formula, The candidate average wet film thickness, To predict the thickness of the cured film, This represents the volume fraction of solids in the varnish. This represents the surface area weight corresponding to the p-th surface sampling point.

7. The method for controlling the spraying of clear coat on automotive bumper skin according to claim 6, characterized in that, The specific steps for predicting the corresponding solidified texture features based on the texture attenuation relationship include: Remove the regional average thickness and low-frequency thickness variation trend from the expected wet film morphology data, and extract the initial texture amplitude of the u-th surface region according to each texture band; When the varnish material and spraying environment are within the corresponding calibration range, the calibrated leveling migration amount is converted according to the average wet film thickness and effective leveling duration using the following formula: ； ； ； In the formula, Let be the leveling migration amount of the u-th curved surface region under the candidate spraying conditions. To calibrate the average wet film thickness, the superscript 'c' indicates the calibration spraying conditions. To calibrate the leveling migration under spraying conditions, and The average wet film thicknesses are those under candidate spraying conditions and those under calibration spraying conditions, respectively. The effective leveling time from the completion of spraying the clear coat to the point where the varnish essentially stops flowing in the u-th curved surface region. To calibrate the effective leveling time for the corresponding curved surface area under spraying conditions, and These are the integrals of the flowability under candidate spraying conditions and calibration spraying conditions, respectively. Let dt represent the equivalent apparent viscosity of the clear coat in the u-th curved region at time t, where t represents the time variable calculated from the time the corresponding curved region is sprayed, and dt is a time infinitesimal element. The following formula predicts the u-th surface region in the... Solidified texture amplitude under each texture band: ； In the formula, To predict the amplitude of the cured texture, The initial texture amplitude is formed by the candidate spraying parameters.

8. The method for controlling the spraying of clear coat on automotive bumper skin according to claim 7, characterized in that, The specific steps for determining the target spraying process parameters include: The candidate spraying process parameters are composed of the spray lane spacing, spray gun posture, clear coat flow rate of each spray lane, and spray gun movement speed. The target spraying process parameters are selected according to the following formula: ； In the formula, This represents the set of candidate spraying process parameters. Let C represent the set of target spraying process parameters, where C represents the feasible set of candidate parameters that satisfy the operation of the spraying equipment, u represents the surface region number, and U represents the total number of surface regions. This represents the target solidified texture amplitude for the corresponding curved surface region and texture band. Indicates the first The allowable target logarithmic amplitude deviation for each texture band.

9. The method for controlling the spraying of clear coat on automotive bumper skin according to claim 8, characterized in that, The specific steps for applying clear coat according to the target spraying process parameters include: Control the spray gun to move along the target spray gun trajectory determined by the target spraying process parameters, and perform clear varnish spraying according to the target clear varnish flow rate and target spray gun moving speed corresponding to each spraying pass; After completing the corresponding spraying passes in each curved area and before the overall spraying of the bumper skin is finished, obtain the actual wet film surface data of the corresponding curved area and determine the actual wet film thickness. When the actual wet film thickness exceeds the allowable wet film thickness range determined by the cured film thickness constraint and the sagging limit thickness, no reverse spraying is performed on the already sprayed curved area, and the clear varnish flow rate or spray gun movement speed of the adjacent spraying lanes that have not yet been executed is adjusted according to the wet film thickness deviation. After all spraying passes are completed, the bumper skin is controlled to enter the curing process according to the target curing process entry time. After the clear coat has cured, the actual cured texture amplitude of each curved area is obtained, and the actual cured texture amplitude is compared with the corresponding target cured texture amplitude to obtain the clear coat spraying quality evaluation result.

10. A system for implementing the method for controlling the spraying of clear coat on an automotive bumper skin as described in any one of claims 1-9, characterized in that, include: The data module acquires the coating surface data of the body exterior covering adjacent to the bumper skin and the curved surface data of the bumper skin, and determines the target texture features of different curved areas of the bumper skin at multiple surface spatial scales. The calibration module is used to apply clear coat to the calibration object corresponding to the bumper skin, obtain the texture features of the clear coat when it is in a wet film state and a cured state, and determine the texture attenuation relationship at different surface spatial scales based on the texture change between the two states. The prediction module is used to determine the expected wet film morphology data of each curved area of ​​the bumper skin based on the candidate spraying process parameters, extract the initial texture features from the expected wet film morphology data, and predict the corresponding cured texture features based on the texture attenuation relationship. The target module is used to determine the target spraying process parameters from the candidate spraying process parameters based on the deviation between the cured texture features and the corresponding target texture features, and in combination with the film-forming constraints of the clear coat coating, so as to perform clear coat spraying on the bumper skin according to the target spraying process parameters.

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