Abstract:
A method for painting a panel using a paint applicator defines a painting pattern with a plurality of points on a surface of a panel to be painted, the pattern extending in a predetermined direction and the points defining opposite edges of the pattern extending in a predetermined direction, with at least one edge of the pattern being adjacent an edge of the panel. The applicator is moved relative to the panel to apply the paint in the painting pattern having a desired film thickness. The pattern including a first plurality of pattern segments and a second plurality of reinforcing segments, the pattern segments being connected together each extending between an associated pair of the points on the opposite edges of the pattern, and the reinforcing segments each extending between an associated pair of the points adjacent the edge of the panel. A plurality of different painting patterns can be stored in a memory for selecting the one pattern to be used.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of the U.S. provisional patent application Ser. No. 60/293,045, filed May 23, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to a method for painting panels and, in particular, to a method for painting the outer panels of an automobile body. 
     Typically, rotary type electrostatic spray painting devices, bell atomizers or applicators that generally apply round or elliptical patterns, are used to paint the outer panels of an automobile body as the body is moved along an assembly line. The desired result is a good painted surface of uniform required film thickness. However, the paint application distribution inherent in bell applicators and the shapes of the body panels present many problems to be overcome. 
     For example, the outer side panels of an automobile body include front and rear wheel openings or cutouts. Thus, portions of these side panels over the wheel openings have a shorter vertical length than other portions. In order to properly paint the shorter portions, one prior art solution is to locate bell applicators above and below a central horizontal plane of the side panels. In this configuration, a distance between the side panel and the spray head is always constant such that a good painted surface is obtained. Since, however, the side panels are divided into two or three portions for painting, four to six spray heads are necessary for one coating. As a result, the painting system requires a large space in which to locate the many spray heads, and the equipment costs are relatively high. 
     Another prior art electrostatic spray painting device has spray heads that move up and down along a vertical line to enable the outer side panels to be painted by one spray head, so that the number of spray heads needed by the painting device is drastically reduced. However, in this painting device, since the spray head moves away from the side panel during reciprocation of the spray head due to a configuration of the side panel, the electrostatic charge of the paint particles may be lost. In this case paint particles that have lost their electrostatic charge will adhere to the side panel and the quality of the painted surface is degraded. 
     Another prior art solution is to spray onto the side panels with spray heads moving along an outline of the panels. Such a configuration requires a programmed movable member that maintains the spray head a uniform distance from the side panel surface and aligns an axis of the spray head substantially perpendicular to the adjacent plane of the side panel. 
     Conventional painting methods use a standard “W” (FIG. 1) wave pattern which results in a trapezoidal film build profile (FIG.  2 ). This pattern is acceptable and desired when meeting additional “W” wave patterns at the edges. When painting the edge of a panel the spray pattern must be significantly extended past the edge of the panel to attain acceptable uniformity or a perpendicular stroke is required to add additional film build at the edges. The perpendicular reinforcement stroke is undesirable because it requires additional machine travel and wasted time moving to and from the start and end of the pattern. 
     SUMMARY OF THE INVENTION 
     The present invention concerns a method for painting a panel using a bell applicator comprising the steps of: providing a bell applicator; providing paint to the applicator; defining a painting pattern with a plurality of points on a surface of a panel to be painted, the pattern extending in a predetermined direction and the points defining opposite edges of the pattern extending in the predetermined direction, at least one edge of the pattern being adjacent an edge of the panel; and moving at least the applicator relative to a panel to apply the paint to the surface of the panel in the predetermined pattern having a desired film thickness, the pattern including a first plurality of pattern segments and a second plurality of reinforcing segments, the pattern segments being connected together each extending between an associated pair of the points on the opposite edges of the pattern, and the reinforcing segments each extending between an associated pair of the points at the at least one edge of the pattern adjacent the edge of the panel. The pattern can include: a “W” shaped triangular pattern formed by the pattern segments; a triangular pattern of substantially vertical ones of the pattern segments alternating with angled ones of the pattern segments; a crossing triangular pattern formed by crossed pairs of the pattern segments; or a square pattern having opposed sides formed by pairs of the pattern segments. 
     The reinforcing segments can include longer reinforcing segments extending in the predetermined direction and shorter reinforcing segments extending transverse to the predetermined direction connecting opposite ends of each of the longer reinforcing segment to the associated pair of points. The method also can include including a third plurality of reinforcing segments each extending in the predetermined direction between an associated pair of the points at another one of the edges of the pattern. A plurality of different painting patterns can be stored and one of the stored patterns selected for performing the method. The pattern segments and the reinforcing segments are applied to the surface of the panel as a continuous pattern including applying the paint continuously to the surface of the panel from a beginning to an end of the pattern. 
     The invention also concerns a system for painting a panel using a bell applicator including: a bell applicator; a source of paint connected to said bell applicator; and a control means connected to said bell applicator for moving at least said bell applicator relative to a panel to apply paint from said source to a surface of the panel in a predetermined pattern having a desired film thickness, said pattern extending in a predetermined direction and including a plurality of connected segments extending between spaced apart points defining opposite edges of said pattern extending in said predetermined direction, at least one of said segments being a reinforcing segment extending in said predetermined direction between a pair of said points at one of said edges of said pattern adjacent an edge of the panel. The pattern is a selected one of a plurality of painting patterns and the system includes a memory connected to said control means for storing said plurality of painting patterns. The system also includes an input device connected to said control means for selecting one of said plurality of painting patterns. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which: 
     FIG. 1 shows a standard “W” wave pattern for a painting method according to the prior art; 
     FIG. 2 is a plot of a paint film build profile produced by the pattern shown in FIG. 1; 
     FIG. 3 shows an edge reinforced pattern for a first embodiment painting method according to the present invention; 
     FIG. 4 is a plot of a paint film build profile produced by the pattern shown in FIG. 3; 
     FIGS. 5 through 15 show additional embodiments of the edge reinforced pattern painting method according to the present invention; and 
     FIG. 16 is a schematic block diagram of a system for performing the painting method according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     There is shown in FIG. 1 a prior art pattern  10  for painting utilizing a bell atomizer or applicator. Currently, the process of painting automobile body panels uses high shaping air to focus the bell pattern. The high shaping air pattern is defined as applications where greater than 200 slpm of shaping air is used to attain a smaller focused bell pattern typically having a fan width less than 15″ wide. Fan width for the process is defined as the width of a paint profile at ½ of the film build of the highest 8″ moving average. A focused fan pattern is used to improve part relative transfer efficiency or to increase particle velocity. 
     The body panel moves along an assembly line past a painting station at which is located a bell atomizer. While either the body panel, or the bell atomizer, or both are moved horizontally, the bell atomizer is operated to deposit a film of paint on the facing surface of the body panel utilizing a series of up and down motions resulting in a “W” pattern  10  as shown in FIG.  1 . The prior art pattern and the patterns according to the present invention are described herein in terms of movement in a plane (horizontal and vertical coordinates) since it is desirable to maintain a constant distance between the bell atomizer and the surface being painted. Thus, the bell atomizer may also be moving along a third axis following a contour of the body panel. 
     Starting at a point A, the bell atomizer painting pattern moves upwardly and to the right to deposit a first pattern segment  11  terminating at a point B. The bell atomizer path then changes direction moving downwardly and to the right from the point B to deposit a second pattern segment  12  terminating at a point C. At the point C, the bell atomizer again changes direction moving upwardly parallel to the segment  11  to deposit a third pattern segment  13  terminating at a point D. Similar movements result in a fourth pattern segment  14  between the point D and a point E, a fifth pattern segment  15  between the point E and a point F, a sixth pattern segment  16  between the point F and a point G, and so on until the panel is completely painted. The segments  11  through  16  typically extend at an angle greater than 45° with respect to horizontal. 
     When the standard “W” wave pattern  10  is used the resulting film forms a trapezoidal film build profile (see FIG.  2 . This pattern is acceptable and desired when meeting additional “W” wave patterns at the edges of the pattern  10 . However, when painting the edge of a panel the spray pattern must be significantly extended past the edge of the panel to attain acceptable uniformity or a perpendicular stroke is required to add additional film build at the edges. This reinforcement stroke is undesirable because it requires additional machine travel and wasted time moving to and from the start and end of the pattern  10 . 
     FIG. 2 is a plot of a trapezoidal paint film build profile  17  produced by the pattern  10  shown in FIG.  1 . The profile  17  represents film thickness “t” along the horizontal axis verses distance or position on the pattern  10  along the vertical or “Y” axis. The thickness increases from no coverage to a maximum amount over a first profile portion  18  representing an area at the edge of the pattern  10  that is not crossed by the full diameter of the fan. A second desired thickness profile portion  19  covers most of the pattern  10  and a third decreasing thickness profile portion  20  is at the opposite edge of the pattern. Although the fan overlaps along most of the pattern  10  as successive segments are traversed, there is no overlap at the edges of the pattern such that the film thickness varies is as shown in the portions  18  and  20 . 
     The improved painting method according to the present invention provides more uniform film builds near the edges of the panels. There are several embodiments where reinforcement strokes can be built into a reciprocating bell application pattern such as: 
     1. A dual edge reinforced triangular approach can be used to provide additional film build for surfaces painted by one machine where the surface has two edges. See the following description of the FIGS. 3,  5 ,  6 ,  11 ,  12 ,  14  and  16 . 
     2. A single edge reinforced triangular approach can be used to provide additional film build for surfaces painted by one machine where the surface has a single edge. See the following description of the FIGS. 7,  8 ,  13  and  15 . 
     3. A dual edge reinforced square wave approach can be used to provide additional film build for surfaces painted by one machine where the surface has two edges. See the following description of the FIGS. 9 and 10. This works best for applications where two coats are applied with a 50/50 film build split. The second coat is inverted and applied directly atop the first coat. 
     The painting method according to the present invention overcomes the shortcomings of the conventional “W” wave pattern  10  by the use of a focused fan pattern high shaping air bell that allows a pattern of bell movement that gives improved film build at the edges without wasted movement time. In these movement patterns the reinforcement stroke is built into the pattern rather than being added afterward. 
     Weave patterns for bell painting have long been used by reciprocating bell machines. Since these machines are restricted in their travel, “W” patterns and square patterns delivering reduced film build or over-spray at the edges has been the norm. Using a robot with significant path capability and a focused pattern bell allows the generation of novel patterns for applying the paint that has improved characteristics. The patterns described below can be executed by a robot and deliver significant reinforcement and additional film build at the edges of the part with minimized over-spray. The patterns are accomplished by making the segment movements shown in the following figures proceeding from point to point in alphabetical order. 
     A first embodiment painting pattern  30  according to the present invention incorporates the segments  11  through  16  of the “W” pattern  10  shown in FIG.  1 . However, a dual edge reinforced triangular approach is used to provide additional film build for surfaces painted by one machine where the surface has two edges. A lower edge pattern reinforcing segment  31  is applied between the points A and G passing through the points C and E. An upper edge pattern reinforcing segment  32  is applied between the points B and F passing through the point D. 
     FIG. 4 is a plot of a paint film build profile  33  produced by the pattern  30  shown in FIG.  3 . The profile  33  is similar to the profile  17  of FIG. 2 in that the film thickness “t” is along the horizontal axis verses distance or position on the pattern  33  along the vertical or “Y” axis. The thickness increases from no coverage to a maximum amount over a first profile portion  34  representing an area at the edge of the pattern  30  that is not crossed by the fill diameter of the fan. A second desired thickness profile portion  35  covers most of the pattern  10  and a third decreasing thickness profile portion  36  is at the opposite edge of the pattern. The reinforcing segments  31  and  32  increase the film thickness in the edge areas represented by the profile portions  34  and  36  as compared with the profile portions  18  and  20 . 
     As shown in FIG. 5, a second embodiment painting pattern  40  according to the present invention is similar to the pattern  30  shown in FIG. 3 but does not require stopping and starting the paint application to separately apply the reinforcing segments  31  and  32 . A plurality of pattern segments  41  through  51  is applied connecting the points A through L without stopping the bell applicator. The segments  42  through  44 ,  50  and  51  are the lower and upper reinforcing segments. 
     As shown in FIG. 6, a third embodiment painting pattern  60  according to the present invention is similar to the pattern  40  shown in FIG. 5 but alternate vertical segments are perpendicular to the reinforcing segments. A plurality of pattern segments  61  through  73  is applied connecting the points A through N without stopping the bell applicator. The segments  62 ,  64 ,  66 ,  68 ,  70  and  72  are the lower and upper reinforcing segments and the alternate vertical segments  61 ,  65 ,  69  and  73  extend perpendicular to the reinforcing segments. 
     As shown in FIG. 7, a fourth embodiment painting pattern  80  according to the present invention is a crossing triangular pattern that does not require stopping and starting the paint application where reinforcing segments are required along only one edge. A plurality of pattern segments  81  through  89  is applied connecting the points A through J without stopping the bell applicator. The segments  84  through  86  are the lower reinforcing segments. This pattern could be inverted to produce upper reinforcing segments. 
     As shown in FIG. 8, a fifth embodiment painting pattern  90  according to the present invention is a crossing triangular pattern similar to the pattern  80  of FIG. 7 that does not require stopping and starting the paint application where reinforcing segments are required along only one edge. A plurality of pattern segments  91  through  99  is applied connecting the points A through J without stopping the bell applicator. The segments  92 ,  95  and  98  are the lower reinforcing segments. This pattern could be inverted to produce upper reinforcing segments. Depending upon the spraying process settings, there can be a problem with too much film thickness at the junctions of the reinforcing segments, such as at the coincident points B and F in FIG.  7 . The pattern  90  eliminates this problem by slightly offsetting the ends of the reinforcing segments as shown by the gap between the points B and F in FIG.  8 . 
     As shown in FIGS. 9 and 10, a sixth embodiment painting pattern  100  and  110  according to the present invention wherein a dual edge reinforced square wave approach can be used to provide additional film build for surfaces painted by one machine where the surface has two edges. The two coats  100  and  110  are applied with a 50/50 film build split with the second coat  110  inverted and applied directly atop the first coat  100 . A plurality of pattern segments  101  through  107  is applied connecting the points A through H without stopping the bell applicator. The segments  102 ,  104  and  106  are the reinforcing segments. A plurality of pattern segments  111  through  117  are applied connecting the points I through P without stopping the bell applicator. The segments  112 ,  114  and  116  are the reinforcing segments. The second coat  110  begins at the point I, which corresponds to the point A in the first coat  100 , and ends at the point P, which corresponds to the point G in the first coat. 
     As shown in FIG. 11, a seventh embodiment painting pattern  120  according to the present invention is a triangular pattern similar to the pattern  40  of FIG. 5 that does not require stopping and starting the paint application. A plurality of pattern segments  121  through  131  is applied connecting the points A through L without stopping the bell applicator. The segments  122 ,  124 ,  126 ,  128  and  130  are the reinforcing segments. 
     As shown in FIG. 12, an eighth embodiment painting pattern  140  according to the present invention is a triangular pattern similar to the pattern  60  of FIG. 6 that does not require stopping and starting the paint application. A plurality of pattern segments  141  through  152  is applied connecting the points A through M without stopping the bell applicator. The segments  141 ,  143 ,  145 ,  147 ,  149  and  151  are the reinforcing segments. 
     As shown in FIG. 13, a ninth embodiment painting pattern  160  according to the present invention is a crossing triangular pattern similar to the pattern  80  of FIG. 7 that does not require stopping and starting the paint application where reinforcing segments are required along only one edge. A plurality of pattern segments  161  through  171  is applied connecting the points A through L without stopping the bell applicator. The short vertical segments  162 ,  164 ,  167  and  169  and the longer horizontal segments  163  and  168  are the upper reinforcing segments. This pattern could be inverted to produce lower reinforcing segments. Except for the ends of the pattern, the short vertical segments will be doubled such as the segments  162  and  169 . 
     As shown in FIG. 14, a tenth embodiment painting pattern  180  according to the present invention is a “W” pattern that does not require stopping and starting the paint application where reinforcing segments are required along both edges. A plurality of pattern segments  181  through  195  is applied connecting the points A through P without stopping the bell applicator. The short vertical segments  181 ,  183 ,  185 ,  187 ,  189 ,  191 ,  193  and  195  and the longer horizontal segments  184 ,  188  and  192  are the reinforcing segments. Except for the ends of the pattern, the short vertical segments will be doubled such as the segments  181  and  187 . 
     As shown in FIG. 15, an eleventh embodiment painting pattern  200  according to the present invention is a triangular pattern similar to the pattern  140  of FIG. 12 that does not require stopping and starting the paint application and where reinforcing segments are required along both edges. A plurality of pattern segments  201  through  216  is applied connecting the points A through Q without stopping the bell applicator. The short vertical segments  201 ,  203 ,  205 ,  207 ,  209 ,  211 ,  213  and  215  and the longer horizontal segments  204 ,  208  and  212  are the reinforcing segments. Except for the ends of the pattern, the short vertical segments will be doubled such as the segments  201  and  207 . 
     There is shown in FIG. 16 a system  220  for performing the method of painting according to the present invention. A bell applicator  221  is moved according to the desired painting pattern by an actuator  222  such as a robot. The actuator  222  is responsive to a control  223  that provides positioning signals. A paint source  224  is connected to the bell applicator  221  through the control  223  to selectively provide paint when required. The control  223  is connected to and responsive to signals generated by a computer  225 . Computer programs for defining the patterns  30 ,  40 ,  60 ,  80 ,  90 ,  100 ,  110 ,  120 ,  140 ,  160 ,  180  and  200  are stored in a memory  226  connected to the computer  225 . An input device  227  also is connected to the computer  225  for storing the programs in the memory  226 , changing the programs as required, selecting the program corresponding to the pattern to be painted and causing the computer  225  to operate the control  223 . 
     Although the method and apparatus according to the present invention have been shown and described in terms of a bell applicator spraying liquid paint, any type of spray applicator can be used. For, example, the applicator  221  shown in FIG. 16 could be a powder spray applicator of either the bell or gun type. Thus, the method and apparatus according to the present invention generally concern applying paint in a pattern with a paint applicator. 
     In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.