阅读说明：本技术 利用喷雾器为工件涂漆的方法以及涂漆系统 (method for painting a workpiece with a sprayer and painting system ) 是由 O·梅尔 于 2018-02-08 设计创作，主要内容包括：本发明涉及一种用于为工件(24)涂漆的方法,在其中,涂装设备(26a、26b)利用喷雾器(32a、32b)将射流(34)指向工件(24),可由涂装设备改变射流的射流几何形状。摄像机(36；36a、36b)拍摄射流(34)的图像(34’)。图像处理装置(38)检测在图像(34’)上拍摄的射流(34)和目标射流之间的偏差。控制装置(40)根据由图像处理装置(38)检测到的偏差控制涂装设备(26a、26b)。(The invention relates to a method for painting a workpiece (24), wherein a painting system (26a, 26b) directs a jet (34) at the workpiece (24) by means of a spray jet (32a, 32b), the jet geometry of which can be varied by the painting system. A camera (36; 36a, 36b) captures an image (34') of the jet (34). An image processing device (38) detects a deviation between the jet (34) taken on the image (34') and the target jet. A control device (40) controls the painting equipment (26a, 26b) according to the deviation detected by the image processing device (38).)

1. A method for painting a workpiece (24), the method having the steps of:

a) a painting device (26a, 26b) which directs a jet (34) at the workpiece (24) by means of a spray jet (32a, 32b), the painting device being able to vary the jet geometry of the jet;

b) A camera (36; 36a, 36b) taking an image (34') of the jet (34);

c) An image processing device (38) detects a deviation between the jet (34) taken on the image (34') and a reference jet;

d) A control device (40) controls the painting equipment (26a, 26b) according to the deviation detected by the image processing device (38).

2. Method according to claim 1, wherein during step b) the optical axis (48) of the camera (36) is oriented at least substantially perpendicular to the longitudinal axis (46) of the nebulizer (32a, 32 b).

3. Method according to claim 1 or 2, wherein painting of the workpiece (24) is interrupted during said step b).

4. a method as claimed in claim 3, wherein during said step b) the test object (44) is painted by the sprayers (32a, 32 b).

5. method according to claim 3 or 4, wherein said step b) is carried out at least when the characteristics of the reference jet are to be changed.

6. The method of any of the above claims, wherein the image processing device (38) determines at least one characteristic of the jet geometry, wherein the characteristic of the jet geometry is selected from the group consisting of:

a width (B) of the jet (34) at a preset distance (A) from the sprayers (32a, 32B),

A maximum angle (alpha) of the jet with respect to a longitudinal axis (46) of the atomizer (32a, 32b) when leaving the atomizer (32a, 32b),

the density distribution of the jet (34) is,

the shape of the outer contour of the jet (34), and

A change in any of the above characteristics over time.

7. method according to any one of the preceding claims, wherein the image processing device (38) edge filters the captured image (34') of the jet (34).

8. Method according to one of the preceding claims, wherein the control device changes at least one of the following control parameters of the coating installation (26a, 26b) in step d):

The pressure of the diverted air discharged by the sprayers (32a, 32b),

The volumetric flow of paint delivered to the sprayer,

the temperature of the paint delivered to the sprayer.

9. a painting system for painting a workpiece (24), the painting system having:

A painting device (26a, 26b) which is designed to direct a jet (34) at the workpiece (24) by means of a spray jet (32a, 32b), the painting device (26a, 26b) being able to change the jet geometry of the jet,

A camera (36a, 36b) arranged to take an image of the jet (34),

An image processing device (38) arranged to detect a deviation between the jet (34) taken on the image (34') and a reference jet,

A control device (40) configured to control the painting equipment (26a, 26b) according to the deviation detected by the image processing device (38).

10. the painting system according to claim 9, wherein the image processing device (38) is configured to determine at least one characteristic of the jet geometry, wherein the characteristic of the jet geometry is selected from the group consisting of;

A width (B) of the jet (34) at a preset distance (A) from the nebuliser (32a, 32B),

A maximum angle (alpha) of the jet with respect to a longitudinal axis (46) of the atomizer (32a, 32b) when leaving the atomizer (32a, 32b),

the density distribution of the jet (34) is,

The shape of the outer contour of the jet (34), and

a change in any of the above characteristics over time.

11. The painting system according to claim 9 or 10, wherein the optical axis (48) of the camera (36) is oriented at least substantially perpendicularly to the longitudinal axis (46) of the sprayers (32a, 32 b).

12. Painting system according to any one of claims 9 to 11, having a painting cabin (12) inside which the sprayers (32a, 32b) are arranged, wherein the cameras (36a, 36b) are arranged outside the painting cabin (12).

13. The painting system according to any one of claims 9 to 12, wherein the control device (40) is provided to vary, in step d), at least one of the following control parameters of the painting installation (26a, 26 b):

The pressure of the diverted air discharged by the sprayers (32a, 32b),

A volumetric flow of paint discharged by the sprayers (32a, 32b),

the temperature of the paint delivered to the sprayers (32a, 32 b).

Technical Field

the invention relates to a method for painting a workpiece by using a sprayer and a painting system. In particular, the present invention relates to the technical problem of optimizing the jet produced by the sprayer with the aim of improving the painting quality and minimizing the amount of paint and overspray used.

background

In order to automatically paint vehicle bodies, shell parts or other workpieces, painting systems are generally used which have a robot and a sprayer which is carried by a movable arm of the robot. The sprayer produces a paint jet directed at the workpiece. By means of a robot, the sprayer is guided over the workpiece along a preset trajectory so that the jet sweeps over the portion of the workpiece to be painted and is uniformly coated with paint.

In the prior art, hydraulic sprayers are known, in which the paint is pressed out through a nozzle with high pressure. On exiting from the nozzle, a turbulent flow is created through which the paint is dispersed into individual droplets. In pneumatic sprayers, the paint is accelerated and pressed out of the nozzle by means of a motive gas. Sprayers are also known in which the paint is accelerated by means of an electric field so that it finally exits from the nozzle.

Most widespread are rotary sprayers, in which the paint is directed onto a very rapidly rotating disk, often also referred to as a bell (glockenter). Due to the centrifugal force, the paint accelerates outward and breaks at the edge of the bell. Thereby, the paint film is broken down into fine droplets.

As a result of the paint being thrown radially outwards, additionally diverted air (Lenkluft) under pressure exits on the atomizer. This diverted air also entrains and diverts paint particles so that an axially forwardly directed jet is formed. Here, diverted air is understood to be the air flow leaving the atomizer. In some sprayers, different air flows exit from the sprayer, which can be influenced independently of one another by means of special rings or hoods.

despite the formation of the jet by the diverted air, in the case of painting by means of a spray gun not all paint particles are usually deposited on the workpiece. The portion of the paint that is not permanently deposited on the workpiece is referred to as overspray. Typically, the painting process is carried out in a painting cabin, where an air flow is generated. This air flow entrains the overspray and guides it to the separating device.

Since the generation of air flow and the separation process lead to high costs and only a part of the overspray can be recovered in the separation process, minimizing the overspray is an important objective when automatically painting workpieces by means of a spray gun.

In addition to forming a jet with diverted air, in order to minimize overspray, paint is often electrostatically charged prior to atomization. By applying a voltage to the workpiece, it is achieved that the workpiece electrostatically attracts the charged paint particles. In this way a greater proportion of paint particles adhere to the workpiece.

A problem in the automated painting of workpieces is that the design of the relative movement and distance between the spray device and the workpiece is limited by the defined spray geometry. The jet geometry can be parameterized by a number of features. This includes, among others: the width of the jet at a predetermined distance from the spray, the maximum angle of the jet relative to the longitudinal axis of the spray when it leaves the spray, the density distribution of the jet, the outer profile of the jet and the variation with time of one of the above-mentioned characteristics. This can lead to painting defects if the jet geometry changes between successive painting processes using the same paint or after changing the paint within a single painting operation. Such painting has the disadvantage that the paint is not applied uniformly to the workpiece in the desired thickness. In this case, it is often necessary to rework the workpiece at a high cost; it may be more desirable to scrap the workpiece for cost reasons.

up to now, efforts have been made to ensure that the desired jet geometry is maintained by visual inspection of the jet geometry by a skilled technician each time the paint is changed or during a single painting process. To this end, the technician directs the jet at the test object under suitable light conditions and changes the control parameters of the painting installation until the desired jet geometry is obtained. However, visual inspection requires a great deal of experience, is relatively time-consuming, and thus does not always lead to repeatable results. In addition, paint is wasted and overspray is generated during inspection.

disclosure of Invention

The object of the invention is to provide a method for painting workpieces and a painting system, by means of which the desired geometry of the jet can be adjusted particularly quickly.

In terms of a method, the object is achieved by a method for painting a workpiece, having the following steps:

a) The coating equipment utilizes the sprayer to direct the jet flow to the workpiece, and the coating equipment can change the jet flow geometry of the jet flow;

b) The camera shoots images of the jet flow;

c) An image processing device detects a deviation between the jet taken on the image and a reference jet;

d) The control device controls the painting apparatus according to the deviation detected by the image processing device.

The present invention is based on the consideration that visual inspection of the jet geometry by a mechanic is automated. The electronic processing of the images of the jet taken by the camera makes it possible to quantify the characteristics of the jet, so that the geometry of the jet is brought close to the theoretical geometry by suitable control of the painting equipment, on the basis of the information thus obtained. Thus, the adjustment of the desired jet geometry may enable control such that a defined jet geometry is produced, which remains unchanged and independent of the changing paint parameters.

since such control can be automatically performed in a very short time, the idle time at the time of paint replacement is shortened. In modern production lines, in which the paint is changed very frequently, a significant increase in productivity can thereby be achieved. Furthermore, less paint is consumed and less overspray is produced as a result of adjusting the desired jet geometry.

since such control can also be performed during the painting process or between successive painting processes using the same paint, the painting quality can be improved and the costs for rework can be reduced by the present invention.

Experiments have shown that during the taking of the image of the jet in step b), the optical axis of the camera should be oriented at least substantially perpendicularly to the longitudinal axis of the nebulizer. The geometry of the jet can then be detected more simply, since the deformation of the geometry is minimized. In principle, however, it is also possible to capture images from oblique viewing angles. However, image evaluation is more complicated due to geometric distortions.

in this connection, the longitudinal axis of the nebulizer is understood to be the axis aligned with the axis of symmetry of the jet. In general, the longitudinal axis is the axis of symmetry of the output nozzle of the nebulizer. In the case of a rotary atomizer, the longitudinal axis is defined by the axis of rotation of the bell cup.

In principle, an image of the jet can be taken during the directing of the jet at the workpiece. This is generally preferred, especially when the control of the jet geometry is performed during the painting process. However, the surface of the workpiece may affect the shape of the jet. At least when the jet geometry is only checked at relatively large time intervals in the manner according to the invention, it is therefore often more appropriate to interrupt the painting of the workpiece during the image acquisition in step b).

During such interruptions, the nebulizer may paint the test object (e.g. the board) during the taking of the image in step b). This achieves a situation which is as close as possible to the actual painting process, but which nevertheless can be repeated precisely. In this case, it is conceivable to additionally record the painted side of the test object by means of the same or another camera. The painting effect obtained here can then also be used to evaluate certain parameters of the jet, such as the density distribution.

It is also possible to use the surface in the cleaning cartridge as a test object. Such a cleaning cartridge is approached by the sprayer for the cleaning process, which is necessary during the paint change.

In order to record the above-mentioned features of the jet geometry, the image processing device edge filters the captured jet image. By determining the outer edge of the jet, particularly important characteristics of the jet geometry can be determined, including the width of the jet at a preset distance from the nebulizer, the maximum angle of the jet when leaving the nebulizer with respect to the longitudinal axis of the nebulizer, and the shape of the outer contour of the jet.

the time-dependent variation of these characteristics can also be obtained if a plurality of images of the jet are taken. It is therefore also conceivable to use a camera for capturing images in an image capture mode in which a plurality of images are captured per second.

If the atomizer is a rotary atomizer, the control device can change at least one of the following control parameters of the painting installation in step d): the pressure of the diverted air discharged by the rotary atomizer, the rotational speed of the rotary atomizer, the volumetric flow and the temperature of the paint delivered to the atomizer. These control parameters have a direct influence on the geometry of the jet and are therefore suitable for influencing the jet geometry so as to minimize deviations from the theoretical geometry.

the invention further provides a painting system for painting a workpiece by means of a painting installation which is designed to direct a jet at the workpiece by means of a spray jet, the painting installation being able to change the jet geometry of the jet. The camera is arranged to take an image of the jet. The image processing means is arranged to detect a deviation between the jet taken on the image and the reference jet. The control device is configured to control the painting equipment according to the deviation detected by the image processing device.

The advantages obtained by the painting system according to the invention refer to the embodiments of the above process.

To prevent overspray from contaminating the camera, the camera may be disposed outside the paint booth. Alternatively, the camera may be arranged inside the painting cabin. Therefore, locations where there is less overspray in the upper region of the paint booth are preferred. If the camera is arranged in the lower region of the painting cabin, a cleaning device, for example a blower device or a liquid cleaning system, can additionally be provided to prevent overspray from contaminating the camera lens. In certain applications, it may also be advantageous to arrange the camera on a movable arm of the robot carrying the nebulizer.

Drawings

The embodiments of the present invention are explained in detail below with reference to the drawings. Wherein:

fig. 1 shows a perspective view of a painting system according to the invention, in which only a part of the painting cabin is shown;

FIG. 2 shows a schematic view of the important components of the painting system according to the invention;

FIG. 3 shows a schematic diagram of how a camera takes an image of a jet directed at a test object;

Fig. 4a to 4d show images taken by a camera in different stages of image processing.

Detailed Description

The entire painting system according to the invention is shown in perspective in fig. 1 and is denoted by 10. The painting system 10 comprises an almost closed painting cabin 12, of which only a few parts are shown for better visibility reasons. In the embodiment shown, the painting cabin 12 comprises a bottom area 14, four side walls 16 (of which only two are shown in fig. 1), and a ceiling, also not shown. The side wall 16 shown on the left is provided with a window 18 allowing the interior space 20 of the painting cabin 12 to be seen. The paint booth 12 is located on a floor structure 20, as is known in the art.

in the exemplary embodiment shown, the bottom region 14 of the painting booth 12 carries a transport system, indicated at 22, on which the workpieces (here the vehicle bodies 24) can be transported in a transport direction. Before painting, the vehicle body 24 is introduced into the painting cabin 12 by means of the conveyor system 22 via a roller shutter or other closable opening and, after painting has ended, is removed again from the painting cabin 12.

on both sides of the conveying system 22, painting installations 26a, 26b are arranged in the painting booth 12. Each painting installation 26a, 26b comprises a robot 28a or 28b, which has a movable robot arm 30a or 30b, respectively. Each robot arm 30a, 30b carries a rotary atomizer 32a, 32b to which liquid paint and compressed air are fed via lines not shown. The paint and compressed air supply is part of the painting installation 26a, 26b and can also be arranged at least partially outside the painting booth 12.

The paint is, for example, a primer for vehicle body color or a varnish that protects a previously applied primer from UV radiation and brightens the surface of the vehicle body 24. The paints used differ not only in their transparency and color, but also in their viscosity and surface tension. Thus, the geometry of the jet 34 generated by the rotary sprayers 32a, 32b is related to the type of paint to be applied. Since the temperature of the paint also affects its viscosity and surface tension, the geometry of the jet 34 and thus the painting effect may vary even if one and the same paint is applied.

to paint the vehicle body 24, the robot arms 30a, 30b move the rotary sprayers 32a, 32b fixed therein quickly along a preset trajectory over the vehicle body 24. The jet 34 generated by the rotary atomizer 32a, 32b is thereby swept over the surface of the vehicle body 24 over a predetermined distance, so that paint particles can be deposited on the surface of the vehicle body. To improve the adhesion of paint particles, the paint particles may be electrically loaded and the vehicle body 24 grounded, as is known in the art.

The painting system 10 known here differs from conventional systems in that the painting process is monitored by means of a first camera 36a and a second camera 36 b. The first camera 36a is fixed outside the painting cabin 12 and takes images of the painting process through the window 18. The second camera 36b is fixed inside the painting booth 12 and is equipped with additional protection (not shown) in order to protect the overspray. In the illustrated embodiment, the cameras 36a, 36b are conventional cameras that capture images in the visible wavelength spectrum.

Fig. 2 shows the essential components of the painting system 10 according to the invention in a schematic view. The first camera 36a is shown above, which is connected to the image processing device 38 via signal lines, the first camera 36a likewise being part of the painting system 10. The image processing device 38 is connected via a further signal line to a control device 40 for the painting installation 26 a. In fig. 2, the image processing device 38 and the control device 40 are shown as separate structural units. It is obvious that these means can also be spatially grouped together and implemented in particular as different modules of a computer program implemented on a microprocessor.

It is suggested in fig. 2 that during the painting process (as shown in fig. 2, top right), the first camera 36a takes an image of the jet 34. The image is processed by the image processing device 38 and compared to the reference jet. Since the position of the robot arm 30a and thus the position of the rotary atomizer 36a at each time is known, the perspective distortion, which is obtained by obliquely observing the jet 34 by the first camera 36a, can be calculated in the image processing device 38. The result is a rectified image 34' of the jet 34, as in fig. 2, which is shown, for example, on a screen 42 of the image processing device 38.

The image 34' of the jet 34 is now processed and geometrically analyzed with suitable image processing algorithms. In the image processing device 38, the geometric parameters derived therefrom are compared with the theoretical parameters of the reference jet. If the deviation between the geometry acquired by the camera 36a and the desired geometry of the jet exceeds a predetermined tolerance, the control algorithm of the control device 40 calculates control commands for the painting installation 26a from this in order to minimize the deviation. For this purpose, the control device 40 can act in particular on the pressure of the diverted air exiting from the rotary atomizer 32a and thus on the volume flow of paint delivered by the rotary atomizer 32a and/or on the temperature of the paint delivered to the rotary atomizer 32 a. It is also conceivable to vary the movement path of the robot arm 30a in order in this way to match the distance between the rotary atomizer 32a and the surface of the vehicle body 24.

Instead of capturing the jet 34 during its direction toward the vehicle body 24, the jet geometry can also be determined in a camera-assisted manner under better reproducible conditions, as is shown, for example, in fig. 3. Here, the jet 34 is directed at a test object 44, which in the simplest case is a plate. At this point, the axis of rotation 46 of the rotary atomizer 32a is oriented by means of the robot arm 30a such that it extends perpendicular to the planar surface of the test object 44. The fixedly arranged camera 36 is located in the vicinity of the test object 44, the optical axis 48 of the camera running parallel to the surface of the test object 44 and perpendicular to the axis of rotation 46 of the rotary atomizer 32 a. The light source, indicated at 50, is oriented such that the main radiation direction of the light source is perpendicular not only to the axis of rotation 46 but also to the optical axis 48.

tests have shown that under these defined conditions, in particular the geometry of the jet 34 can be precisely acquired by means of the camera 36. Paint particles are well visible by illuminating the jet 34 transverse to the optical axis 48 of the camera 36 by means of a light source 50. The distinctiveness of the paint particles is aided when there is a screen 52 on the side opposite the camera 36 that is illuminated as uniformly as possible.

In fig. 3, the important geometric features of the jet 34 are shown, which can be derived from the image recorded by means of the camera 36. The width B of the jet 34 in the distance a from the rotary atomizer 32a is shown, as well as the opening angle a of the jet directly on the bell disc 54 of the rotary atomizer 32 a.

Fig. 4a to 4d show images of the jet 34 in different stages of image processing. In fig. 4a, a binary image obtained from a captured color image by applying a simple filtering algorithm is shown. For this purpose, the color image is first converted into a grayscale image. The pixel obtains a color of white or black depending on whether the gray value is above or below a preset threshold.

In fig. 4b, the disturbing pixels not belonging to the jet are removed. To do this, the algorithm removes all objects whose size is outside the threshold. Thereby simultaneously removing image noise and smoothing the outer contour of the jet 34.

By means of another algorithm, larger objects not belonging to the jet are removed, thereby obtaining the image of the jet shown in fig. 4 c.

next, an edge detection algorithm is performed to obtain the profile of the jet, which is shown for example in fig. 4 d. Now, with the aid of known algorithms, the characteristics of the jet geometry shown in fig. 3 can be derived from the outer contour of the jet and compared with theoretical values. For example, the theoretical values can be derived from the jet images which have been recorded and which lead to a good painting effect of the relevant workpiece. Furthermore, alternatively, the theoretical value can be determined from a functional relationship, which is present, for example, in the form of a table and is based on empirical values obtained over a long period of time. Such empirical values may also be stored in the expert system, which then outputs the appropriate theoretical values.

after the comparison, the robot arm 30a again introduces the rotary atomizer 32a into the correct processing position with respect to the vehicle body 24. If the deviation determined between the shot jet and the reference jet is not very limited by tolerances, the painting process is continued by means of the changed control parameters.

The painting system 10 can be controlled such that the above-mentioned check of the jet geometry is always carried out when the properties of the reference jet should be changed. In addition to its geometry, the properties of the reference jet also include the paint used. Thus, inspection is typically performed after each color change and each workpiece type change.

However, regular checks (if necessary additional) can also be considered, since the properties of the paint and thus the geometry of the jet also change during temperature changes.