CN103521410A - Method for automatically spray painting three-dimensional patterns on vehicle body surface - Google Patents

Abstract

The invention discloses a method for automatically spray painting three-dimensional patterns on a vehicle body surface, and belongs to the field of vehicle digital design and manufacturing. The method for automatically spray painting the three-dimensional patterns on the vehicle body surface includes the steps of setting up a vehicle outer covering piece model through three-dimensional design software, dispersing the vehicle outer covering piece model into a triangular mesh model, thereby setting up the mapping relation between the triangular mesh model and a planar parameter region, inversely mapping points, corresponding to pattern pixel points, in the planar parameter region onto a vehicle body three-dimensional model based on the mapping relation, setting up the corresponding relation between the pattern pixel points and vehicle body three-dimensional points, storing color information of pixels, generating spray paint paths on the vehicle body three-dimensional model, adjusting the spray paint colors of the patterns according to the pixel color information corresponding to the path points, and then completing the process of automatically spray painting the three-dimensional patterns on the vehicle body surface by driving a spray painting robot. Various individualized patterns are automatically spray painted on the vehicle body surface under the control of a computer according to the spray painting paths generated through the method, and the principle is simple, the spray painting is even, the patterns are vivid, and the pattern spray painting efficiency is effectively improved.

Description

The automatic method for spray-drawing of bodywork surface three-D pattern

Technical field

The present invention relates to a kind of automatic method for spray-drawing of bodywork surface three-D pattern, belong to vehicle Design of digital and manufacture field, be particularly useful for the aspects such as the air brushing of special vehicle camouflage color, ads. on vehicle making and personalized body-finishing.

Technical background

Along with the develop rapidly of producing, auto industry has become the important pillar industry of Chinese national economy, and the different bodywork surface printing pattern of form has potential application widely at aspects such as the drafting of special vehicle camouflage color, ads. on vehicle making and personalized body-finishings.Common vehicle body method for generating pattern has two kinds, a kind of is to utilize plastics or papery pattern directly to stick on bodywork surface, but the impact that changed by bodywork surface curvature, Pattern paste paper is easily wrinkling in taping process, directly affect the aesthetic property of pattern, and Pattern paste paper also easily fades and comes off; Another kind method is manual pattern air brushing, utilize various openworking templates to go out corresponding pattern in the air brushing of vehicle body table, this is also the main method for spray-drawing of current vehicle body camouflage color, although case that this kind of method drawn is true to nature, the retention time is long, production efficiency is low, labour intensity is large.U.S.'s patent of invention " Spray-painting system with automatic color calibration " of people's applications such as Cleary (patent No.: 5434604) can realize the automatic air brushing of various colors, but and the unrealized pattern air brushing at three-dimensional object surface.Up to the present, the automatic method for spray-drawing that does not also occur the bodywork surface three-D pattern that layout directly drives.

Summary of the invention

In order to overcome existing vehicle body method for making pattern in the deficiency aspect production efficiency, pattern fidelity, the invention provides a kind of automatic method for spray-drawing of bodywork surface three-D pattern, to realize by layout driving, computer, automatically control shower nozzle and carry out pattern air brushing at bodywork surface, improve the air brushing efficiency of vehicle body pattern.

The technical solution adopted in the present invention is: a kind of automatic method for spray-drawing of bodywork surface three-D pattern, first utilize the vehicle exterior cladding element model of the Three-dimensional Design Software structure air brushing of wanting, and be separated into triangle grid model, and then set up the mapping relations one by one between triangle grid model and plane parameter territory; Set up thus contacting between layout and Planar Mapping territory, and then the corresponding relation between definite pattern image vegetarian refreshments and the coordinate of parameter plane territory mid point; Corresponding points inverse mapping by pattern image vegetarian refreshments in plane domain, to the threedimensional model of vehicle body, is set up the corresponding relation between pattern image vegetarian refreshments and vehicle body three-dimensional point, and preserves the colouring information of pixel simultaneously; On vehicle body threedimensional model, generate air brushing path, and put according to path the air brushing color that corresponding picture-element color information is adjusted pattern, drive thus air brushing robot to complete the automatic air brushing of bodywork surface three-D pattern; Concrete implementation step is:

(1) first, in CAD design software, set up the three-dimensional CAD model of vehicle body parts, and save as the triangle grid model of STL form, the driving model using it as whole spraying and painting system;

(2) by the stamping inverse process of body outer skin is simulated, three-dimensional autobody surface is flattened on two dimensional surface; The Newton-Raphson residual force equilibrium iteration of setting up the nonlinear finite element of contrary forming process solves form, and realizing is the rapid solving of grid flat to plane blank shape; The object function of iterative is:

$R\left(U\right)=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\left(\right\{F_{\mathrm{ext}}^i\}-\left(F_{\mathrm{int}}^i\right))=0$

In formula, U is global coordinate system lower node virtual displacement vector,

with

be external force and the internal force on i node; The process stop criterion of above-mentioned iteration is:

${\left|\right|R_t\left(u^i\right)-R_t\left(u^{i-1}\right)\left|\right|}_{\∞}\≤\mathrm{\ϵ}$

In formula, R _tfor the residual force factor on node section, ε is given iteration precision;

(3) utilize rotation, translation, zoom operations that two-dimensional design pattern is placed into the ideal position on plane grid; The searching method of employing based on bounding box obtains the tri patch at pixel place fast;

(4) obtain the plane triangle at pixel place

with corresponding spatial triangle

after, the method for employing bilinear interpolation, realizes pattern point q to the mapping of bodywork surface corresponding points p;

(5) according to the resolution requirement of printing pattern, pattern is separated into air brushing unit, extract the center q point of air brushing unit and also store its color information, by step (4), air brushing central point is mapped to and on autobody surface, obtains corresponding points p; The air brushing of arriving vehicle body according to shower nozzle again, apart from d, obtains the movement position point p of shower nozzle _cL; Movement position point { the p that connects all shower nozzles _cLformation air brushing movement locus S _path, by S _paththe motion control unit that is input to air brushing robot is realized the automatic air brushing of pattern.

The invention has the beneficial effects as follows: the automatic method for spray-drawing of this bodywork surface three-D pattern utilizes the vehicle exterior cladding element model of the Three-dimensional Design Software structure air brushing of wanting, and be separated into triangle grid model, and then set up the mapping relations one by one between triangle grid model and plane parameter territory; Set up thus contacting between desirable layout and Planar Mapping territory, and then the corresponding relation between definite pattern pixel and the coordinate of parameter plane territory mid point; Corresponding points inverse mapping by pattern image vegetarian refreshments in plane domain, to the threedimensional model of vehicle body, is set up the corresponding relation between pattern image vegetarian refreshments and vehicle body three-dimensional point, and preserves the colouring information of pixel simultaneously; On vehicle body threedimensional model, generate air brushing path, and put according to path the air brushing color that corresponding picture-element color information is adjusted pattern, drive thus air brushing robot to complete the automatic air brushing of bodywork surface three-D pattern.The air brushing track that this automatic method for spray-drawing generates can automatically complete various individualized patterns in the automatic air brushing of bodywork surface under computer control, and principle is simple, and air brushing is even, and pattern is true to nature, has effectively improved the efficiency of pattern air brushing.

Accompanying drawing explanation

Fig. 1 is spraying and painting system schematic diagram.

Fig. 2 is the flow chart that whole method for spray-drawing is realized.

Fig. 3 is grid model (STL) model of certain a vehicle body bonnet.

Fig. 4 is the vehicle body grid model after flattening.

Fig. 5 is the black and white chessboard grid pattern that is usually used in new car camouflage.

Fig. 6 is for flattening the corresponding relation between vehicle body and pattern.

Fig. 7 divides for flattening the bounding box of vehicle body grid.

Fig. 8 is the camouflage pattern of bonnet.

Fig. 9 is air brushing track.

The specific embodiment

With reference to accompanying drawing and implementation step, specific embodiment of the invention is described in detail.The schematic diagram of spraying and painting system as shown in Figure 1.The present invention will generate the movement locus that can drive air brushing robot to carry out air brushing, and the flow process of whole method as shown in Figure 2.Specific implementation process is as follows:

1, first, at CAD design software, set up the three-dimensional CAD model of vehicle body parts as the driving model of whole spraying and painting system in as UG, CATIA etc.; Utilize the data output function of CAD design software, parameters C AD model is output as to triangle grid model, and save as STL form, as shown in Figure 3.

2, by the stamping inverse process of body outer skin is simulated, three-dimensional autobody surface is flattened on two dimensional surface; The basic thought of method is: the vehicle body grid surface that can not open up is assumed to be the sheet metal curved surface that elastic-plastic deformation occurs, suppose that the suffered impulse force of sheet metal is that ratio loads, material is subject to planar film stress, so just can by parallel computing problem abstract be elastoplasticity full dose problem; And then from the principle of virtual work, utilize Non-Linear Continuous Medium Mechanics theoretical, and the Newton-Raphson residual force equilibrium iteration of setting up contrary shaping nonlinear finite element solves form, and realizing is the rapid solving of grid flat to plane blank shape; The object function of iterative is:

$R\left(U\right)=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\left(\right\{F_{\mathrm{ext}}^i\}-\left(F_{\mathrm{int}}^i\right))=0$

In formula, U is global coordinate system lower node virtual displacement vector,

with

be external force and the internal force on i node.The process stop criterion of above-mentioned iteration is:

${\left|\right|R_t\left(u^i\right)-R_t\left(u^{i-1}\right)\left|\right|}_{\∞}\≤\mathrm{\ϵ}$

In formula, R _tfor the residual force factor on node section, ε is given iteration precision.Fig. 4 is the grid surface that utilizes said method to flatten.

3, utilize rotation, translation, zoom operations by two-dimensional design pattern (as shown in Figure 5, this pattern is elected as through being usually used in the black and white chessboard grid pattern of new car camouflage) be placed into the ideal position on plane grid, the corresponding relationship between air brushing region and four angle points of two-dimensional pattern or other characteristic points is treated in foundation, as shown in Figure 6.By the mode of linear interpolation, determine the corresponding relation of putting on layout and plane grid.

4, find soon the triangle gridding at pattern point place, the process in order to accelerate to find, proposes the searching method based on bounding box especially: as shown in Figure 7, and the minimum bounding box [x of Calculation Plane grid first _min, x _max] * [y _min, y _max], then according to grid vertex, count n _pand coefficient k, the length of side L calculating according to following formula:

$L=\sqrt{\frac{k}{n_p}(x_{\max }-x_{\min })(y_{\max }-y_{\min })}$

The even division of realization to vehicle body plane grid, is divided into a lot of equal-sized square subregions, and is set up following data structure:

Store the correlation between sub-bounding box and grid vertex.On the basis of dividing at above-mentioned bounding box, can find fast the bounding box Bin[i at the corresponding points place of pixel on plane grid] [j], find thus from its nearest summit, and then in a ring tri patch neighborhood of this grid vertex, find the tri patch at this place.

5, obtain pixel corresponding points q _jthe tri patch at place

after, just can find fast its corresponding space triangular dough sheet according to the corresponding relation between plane grid and space lattice

by the space lattice of setting up in the 2nd step and the mapping relations between plane grid

just can be by q _jbe mapped on vehicle body three-dimensional grid,

$f^{-1}:({\mathrm{\Δ}}_i^P\→{\mathrm{\Δ}}_i^S)q_j=p_j$

Thereby utilize above-mentioned Formula layout point and three-dimensional vehicle body point p _jbetween corresponding relation.For the convenience of calculating, can adopt the method for bilinear interpolation as shown in Figure 6, realize pattern corresponding points q _jto bodywork surface corresponding points p _jmapping, computing formula is as follows:

$\left\{\begin{array}{c}p=v_5+t(v_6-v_5)\\ t=\left|\right|g_4-g_2\left|\right|/\left|\right|g_3-g_2\left|\right|\\ v_5=v_2+s(v_1-v_2),v_6=v_3+s(v_1-v_3)\\ s=\left|\right|g_0-g_4\left|\right|/\left|\right|g_1-g_4\left|\right|\\ g_4=(g_0-{\mathrm{wg}}_1)/(1-w)\\ w=\left|\right|(g_0-g_2)\×(g_3-g_2)\left|\right|/\left|\right|(g_1-g_2)\×(g_3-g_2)\left|\right|\end{array}\right.$

Utilize pattern after said method mapping as shown in Figure 8.

6, according to the resolution requirement of printing pattern, pattern is separated into air brushing unit, extracts the center q point of air brushing unit and store its color information, utilize the vehicle body grid surface of (5) foundation and the mapping relations between pattern point, air brushing central point is mapped on autobody surface, obtains corresponding points p.Again according to shower nozzle apart from the air brushing of vehicle body apart from d, obtain the movement position point p of shower nozzle _cL, computing formula is as follows:

p _CL=p+dn _p

Movement position point { the p that connects all shower nozzles _cLformation air brushing movement locus S _path, as shown in Figure 9.

7, by air brushing movement locus S _paththe motion control unit that is input to air brushing robot is realized, the automatic air brushing of pattern.

Claims (1)

1. the automatic method for spray-drawing of a bodywork surface three-D pattern, it is characterized in that: the vehicle exterior cladding element model that first utilizes the air brushing of wanting of Three-dimensional Design Software structure, and be separated into triangle grid model, and then set up the mapping relations one by one between triangle grid model and plane parameter territory; Set up thus contacting between layout and Planar Mapping territory, and then the corresponding relation between definite pattern image vegetarian refreshments and the coordinate of parameter plane territory mid point; Corresponding points inverse mapping by pattern image vegetarian refreshments in plane domain, to the threedimensional model of vehicle body, is set up the corresponding relation between pattern image vegetarian refreshments and vehicle body three-dimensional point, and preserves the colouring information of pixel simultaneously; On vehicle body threedimensional model, generate air brushing path, and put according to path the air brushing color that corresponding picture-element color information is adjusted pattern, drive thus air brushing robot to complete the automatic air brushing of bodywork surface three-D pattern; Concrete implementation step is:

(1) first, in CAD design software, set up the three-dimensional CAD model of vehicle body parts, and save as the triangle grid model of STL form, the driving model using it as whole spraying and painting system;

(2) by the stamping inverse process of body outer skin is simulated, three-dimensional autobody surface is flattened on two dimensional surface; The Newton-Raphson residual force equilibrium iteration of setting up the nonlinear finite element of contrary forming process solves form, and realizing is the rapid solving of grid flat to plane blank shape; The object function of iterative is:

$R\left(U\right)=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\left(\right\{F_{\mathrm{ext}}^i\}-\left(F_{\mathrm{int}}^i\right))=0$

In formula, U is global coordinate system lower node virtual displacement vector,

with

be external force and the internal force on i node; The process stop criterion of above-mentioned iteration is:

${\left|\right|R_t\left(u^i\right)-R_t\left(u^{i-1}\right)\left|\right|}_{\∞}\≤\mathrm{\ϵ}$

In formula, R _tfor the residual force factor on node section, ε is given iteration precision;

(3) utilize rotation, translation, zoom operations that two-dimensional design pattern is placed into the ideal position on plane grid; The searching method of employing based on bounding box obtains the tri patch at pixel place fast;

(4) obtain the plane triangle at pixel place with corresponding spatial triangle

after, the method for employing bilinear interpolation, realizes pattern point q to the mapping of bodywork surface corresponding points p;

(5) according to the resolution requirement of printing pattern, pattern is separated into air brushing unit, extract the center q point of air brushing unit and also store its color information, by step (4), air brushing central point is mapped to and on autobody surface, obtains corresponding points p; The air brushing of arriving vehicle body according to shower nozzle again, apart from d, obtains the movement position point p of shower nozzle _cL; Movement position point { the p that connects all shower nozzles _cLformation air brushing movement locus S _path, by S _paththe motion control unit that is input to air brushing robot is realized the automatic air brushing of pattern.

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