METHOD FOR ASSESSING A SHAPE OF A BELL-SHAPED LIQUID SPRAY

Abstract

Disclosed herein is a method for assessing a shape of a bell-shaped liquid spray, including the steps of operating a spray nozzle for delivering a bell-shaped liquid spray and capturing an image of a plurality of liquid jets forming the delivered bell-shaped liquid spray during operation of the spray nozzle, and a computer program product for assessing a bell-shaped liquid spray.

Claims

1. A method for assessing a shape of a bell-shaped liquid spray, comprising the steps of: operating a spray nozzle for delivering a bell-shaped liquid spray; capturing an image of a plurality of liquid jets forming the delivered bell-shaped liquid spray during operation of the spray nozzle; processing the captured image, wherein processing the captured image comprises converting the captured image to a binary image, the binary image comprising a plurality of filaments, each filament corresponding to a liquid jet and a plurality of arcs, each arc connecting two filaments being located next to each other; and deriving at least one shape parameter of the liquid jets from the processed image.

2. The method according to claim 1, wherein a lateral view image and/or a partial image of the spray nozzle and the plurality of liquid jets is captured.

3. The method according to claim 1, wherein deriving the at least one shape parameter comprises calculating a distance between a determined first point of a first arc and a determined second point of a second arc, the first arc and the second arc being located on opposite sides of a filament and connected to the filament, and using the calculated distance as the at least one shape parameter, the at least one shape parameter indicating a diameter of the corresponding liquid jet.

4. The method according to claim 3, wherein determining the first point and the second point comprises both minimizing the calculated distance between the first point and the second point and, at the same time, maximizing a distance of the first point and the second point from the filament, respectively.

5. The method according to claim 1, wherein deriving the at least one shape parameter comprises isolating a filament, calculating a length of the isolated filament and using the calculated length as the at least one shape parameter, the at least one shape parameter indicating a length of the corresponding liquid jet, and/or calculating a plurality of widths of the isolated filament along a longitudinal extension of the isolated filament and using the plurality of calculated widths as the at least one shape parameter, the at least one shape parameter indicating a longitudinal evolution of the width of the corresponding liquid jet.

6. The method according to claim 5, wherein isolating the filament comprises removing the plurality of arcs from the binary image.

7. The method according to one claim 1, wherein deriving the at least one shape parameter comprises extracting a filament from the binary image and using the shape of the filament as the at least one shape parameter, the at least one shape parameter indicating a trajectory of the corresponding liquid jet.

8. The method according to claim 1, wherein a sequence of images is captured over a period of time and deriving the at least one shape parameter comprises calculating a whipping frequency of an aligned filament of the corresponding binary images by applying a fast Fourier transformation to the aligned filament and using the calculated whipping frequency as the at least one shape parameter, the at least one shape parameter indicating a whipping frequency of the corresponding liquid jet.

9. The method according to claim 8, wherein aligning the filament comprises arranging an extracted filament in a cartesian coordinate system and/or correcting an angle of an extracted filament with respect to a shape of the spray nozzle.

10. The method according to claim 1, wherein deriving the at least one shape parameter comprises removing an intersecting filament from the binary image.

11. The method according to claim 1, wherein the at least one shape parameter is used as an input for numerically simulating a bell-shaped liquid spray and/or as a verification means for a numerically simulated bell-shaped liquid spray.

12. The method according to claim 1, wherein the derived at least one shape parameter is used for assessing a dependence of the at least one shape parameter on a rotational speed of the spray nozzle or on a feeding rate of the liquid or from an airflow.

13. The method according to claim 1, wherein the method is carried out by a processor executing a program code implementing the method.

14. A computer program product for assessing a shape of a bell-shaped liquid spray, comprising a data carrier storing a program code to be executed by a processor, the program code implementing a method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG. 1 shows a schematic illustration of a lateral view of a bell-shaped liquid spray assessment configuration according to the invention;

[0036] FIG. 2 shows an image captured by the high-speed camera of the bell-shaped liquid spray assessment configuration shown in FIG. 1;

[0037] FIG. 3 shows a first binary image the captured image shown in FIG. 2 has been converted to;

[0038] FIG. 4 shows a second binary image the captured image shown in FIG. 2 has been converted to;

[0039] FIG. 5 shows a coordinate system comprising a plurality of aligned filaments;

[0040] FIG. 6 shows a schematic illustration of a top view of a numerically simulated bell-shaped liquid spray according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0041] FIG. 1 shows a schematic illustration of a lateral view of a bell-shaped liquid spray assessment configuration according to the invention. The bell-shaped liquid spray assessment configuration comprises a liquid spray configuration with a conical spray nozzle 10 for delivering a bell-shaped liquid spray 30. The bell-shaped liquid spray configuration may be used, for instance, by a car manufacturer for applying a liquid coating onto a surface of a car body part (not shown).

[0042] Furthermore, the bell-shaped liquid spray assessment configuration comprises a high-speed camera 20. The high-speed camera 20 is arranged such that an optical axis 21 of the high-speed camera extends transverse to an outer lateral surface of the bell-shaped liquid spray 30. The bell-shaped liquid spray assessment configuration may be used to assess a shape of the bell-shaped liquid spray 30.

[0043] The bell-shaped liquid spray assessment configuration further comprises a computer (not shown). The computer has a processor and a memory comprising a program code, the program code implementing a method for assessing a shape of a bell-shaped liquid spray 30 and being executable by the processor. The program code may have been installed in the memory of the computer from a computer program product for assessing a shape of a bell-shaped liquid spray 30 according to the invention, the computer program product comprising a data carrier like a DVD or an USB stick storing the program code. The computer is connected to the high-speed camera 20 for receiving one or more captured images 40 (see FIG. 2) from the high-speed camera 20.

[0044] The bell-shaped liquid spray assessment configuration is configured for carrying out a method for assessing a shape of the bell-shaped liquid spray 30 according to the invention. The method comprises the following steps.

[0045] The bell-shaped liquid spray 30 is delivered by the spray nozzle 10 during a normal operation of the bell-shaped liquid spray configuration. During the normal operation the spray nozzle 10 rotates at an angular speed in a range about from 10.000 rotations per minute (rpm) to 30.000 rpm about a rotation axis. While the spray nozzle 10 is rotating a liquid, preferably a coating, is continuously fed to the spray nozzle 10 at a feeding rate in a range about from 50 ml/min to 200 ml/min.

[0046] During the operation of the spray nozzle 10 the high-speed camera 20 captures an image 40 (see FIG. 2) of the delivered bell-shaped liquid spray 30.

[0047] FIG. 2 shows an exemplary image 40 captured by the high-speed camera 20 of the bell-shaped liquid spray assessment configuration shown in FIG. 1. The captured image 40 is a partial lateral view of the spray nozzle 10 and the bell-shaped liquid spray 30. The captured image 40 comprises a plurality of liquid jets 31 forming the delivered bell-shaped liquid spray 30.

[0048] In further steps of the method the captured image 40 is processed by the computer and at least one shape parameter of the liquid jets 31 is derived from the processed image.

[0049] Processing the captured image 40 comprises converting the captured image 40 to a binary image 50 (see FIG. 3), 51 (see FIG. 4). The processing may comprise a pre-processing of the captured image 40 like applying one or more graphic filter algorithms to the captured image 40 in order to increase a contrast of the captured image 40 or to sharpen the captured image 40. The processing may also comprise a post-processing of the binary image 50 like thickening and/or coloring the filaments 60 and/or arcs 70 in order to facilitate an automatic pattern recognition.

[0050] FIG. 3 shows a first binary image 50 the captured image 40 shown in FIG. 2 has been converted to. The binary image 50 comprises a plurality of filaments 60. Each filament 60 corresponds to a liquid jet 31. The binary image 50 further comprises a plurality of arcs 70. Each arc 70 connects two filaments 60 being located next to each other. As a first shape parameter a diameter of a liquid jet 31 may be derived from the first binary image 50.

[0051] Deriving the first shape parameter comprises calculating a distance 73 between a determined first point 71 of a first arc 70 and a determined second point 72 of a second arc 70, the first arc 70 and the second arc 70 being located on opposite sides of a filament 60 corresponding to the liquid jet 31 connected to the filament 60. Determining the first point 71 and the second point 72 comprises both minimizing the calculated distance 73 between the first point 71 and the second point 72 and, at the same time, maximizing a distance of the first point 71 and the second point 72 from the filament 60, respectively.

[0052] The distance 73 may be calculated by counting a number of pixels between the first point 71 and the second point 72 and then transforming the counted number of pixels to a distance 73 by using a resolution of the binary image. The calculated distance 73 is used as the first shape parameter indicating a diameter of the corresponding liquid jet 31.

[0053] Deriving the first shape parameter may further comprise averaging the calculated distance 73 over a large number filaments 60 and connecting arcs 70 in order to increase an accuracy of the first shape parameter.

[0054] FIG. 4 shows a second binary image 51 the captured image 40 shown in FIG. 2 has been converted to. The second binary image 51 comprises a plurality of filaments 60. Each filament 60 corresponds to a liquid jet 31. As a second parameter a length of a liquid jet 31 may be derived from the second binary image 51.

[0055] Deriving the second parameter comprises removing intersecting filaments from the binary image 50 and isolating a filament 60 corresponding to the liquid jet 31, calculating a length 63 of the isolated filament 60. Isolating the filament 60 comprises removing the plurality of arcs 70 from the binary image 51.

[0056] The length of the isolated filament 60 may be calculated by counting a number of pixels between a first end point 61 of the filament 60 and a second end point 62 of the filament 60 and then transforming the counted number of pixels to a length by using a resolution of the binary image 51. The calculated length 63 is used as the second shape parameter indicating a length of the corresponding liquid jet 31.

[0057] Deriving the second shape parameter may further comprise averaging the calculated length 63 over a large number filaments 60 in order to increase an accuracy of the second shape parameter.

[0058] As a third shape parameter a longitudinal evolution of the width of the corresponding liquid jet 31 may be derived from the second binary image 51. Deriving the third shape parameter comprises calculating a plurality of widths of the isolated filament 60 at a plurality of longitudinal positions along a longitudinal extension of the isolated filament 60.

[0059] The width of the isolated filament 60 at a longitudinal position of the isolated filament 60 may be calculated by counting a number of pixels of the isolated filament 60 crosswise to a longitudinal direction of the isolated filament 60 and then transforming the counted number of pixels to a width by using a resolution of the second binary image 51. The plurality of widths is used as the third shape parameter.

[0060] Deriving the third shape parameter may further comprise averaging the calculated longitudinal evolutions of width over a large number filaments 60 in order to increase an accuracy of the third shape parameter.

[0061] As a fourth parameter a trajectory of a liquid jet 31 may be derived from the second binary image 51. Deriving the fourth shape parameter comprises removing intersecting filaments from the binary image 50 and extracting a filament 60 corresponding to the liquid jet 31 from the binary image 50 and may comprise correcting an angle of the extracted filament 60 with respect to a shape of the spray nozzle 10. The shape of the filament 60 is used as the fourth shape parameter indicating a trajectory of the corresponding liquid jet 31.

[0062] Deriving the fourth shape parameter may further comprise averaging the shape over a large number filaments 60 in order to increase an accuracy of the fourth shape parameter.

[0063] FIG. 5 shows a coordinate system comprising a plurality of aligned filaments 60. As a fifth parameter whipping frequency of a liquid jet 31 is derived from the cartesion coordinate system 80.

[0064] Deriving the fifth parameter is based on a sequence of images 40 being captured over a period of time and comprises calculating a whipping frequency of an aligned filament 60 corresponding to the liquid jet 31 of the corresponding binary images 50 by applying a fast Fourier transformation to the aligned filament 60. Aligning the filament 60 comprises removing intersecting filaments from the binary image 50, extracting a filament 60 corresponding to the liquid jet 31 from the binary image 50 and arranging the extracted filament 60 in the cartesian coordinate system 80 and may comprise correcting an angle of the extracted filament 60 with respect to a shape of the spray nozzle 10. The calculated whipping frequency is used as the fifth shape parameter indicating a whipping frequency of the corresponding liquid jet 31.

[0065] Deriving the fifth shape parameter may further comprise averaging the calculated whipping frequency over a large number filaments 60 per image 40 in order to increase an accuracy of the fifth shape parameter.

[0066] FIG. 6 shows a schematic illustration of a top view of a numerically simulated bell-shaped liquid spray 90 according to the invention. In still another step the derived shape parameters are used as an input for numerically simulating a bell-shaped liquid spray 90 or as a verification means for a numerically simulated bell-shaped liquid spray 90, the bell-shaped liquid spray 90 having a plurality of numerically simulated liquid jets 91. Additionally, the derived at least one shape parameter may be used for assessing a dependence of the at least one shape parameter on a rotational speed of the spray nozzle 10 or on a feeding rate of the liquid or from an airflow.

REFERENCE NUMERALS

[0067] 10 spray nozzle [0068] 20 high-speed camera [0069] 21 optical axis [0070] 30 bell-shaped liquid spray [0071] 31 liquid jet [0072] 40 captured image [0073] 50 binary image [0074] 51 binary image [0075] 60 filament [0076] 61 first end point [0077] 62 second end point [0078] 63 length [0079] 70 arc [0080] 71 first point [0081] 72 second point [0082] 73 distance [0083] 80 cartesian coordinate system [0084] 90 numerically simulated bell-shaped spray [0085] 91 numerically simulated liquid jets