METHOD FOR ASSESSING A DOTTING OF A SURFACE

Abstract

Disclosed herein is a method for assessing a dotting of a surface, comprising including the steps of gradually dotting the surface during a predetermined interval of time and capturing a plurality of images of the dotted surface during the predetermined time interval. Also disclosed herein is a computer program product for assessing a dotting of a surface.

Claims

1. A method for assessing a dotting of a surface, comprising the steps of: gradually dotting the surface during a predetermined interval of time; capturing a plurality of images of the dotted surface during the predetermined time interval; successively processing the plurality of images; and deriving at least one dotting parameter value from the processed plurality of images.

2. The method according to claim 1, wherein dotting the surface comprises covering the surface with a plurality of droplets of a liquid spray or chipping the surface with a plurality of projectiles.

3. The method according to claim 1, wherein processing an image comprises pre-processing the captured image and converting the pre-processed image into a binary image.

4. The method according to claim 3, wherein the pre-processed image is converted both into a first binary image using a first higher sensitivity and into a second binary image using a second lower sensitivity.

5. The method according to claim 4, wherein deriving the at least one dotting parameter value comprises combining a first dotting parameter value derived from the first binary image and a second dotting parameter value derived from the second binary image.

6. The method according to claim 4, wherein successively processing the plurality of images comprises stopping processing when a number of dots in the second binary image is larger than a number of dots in the first binary image.

7. The method according to claim 1, wherein a number of dots or a number of small dots is derived as the at least one dotting parameter value.

8. The method according to claim 1, wherein a dot diameter is derived as the at least one dotting parameter value.

9. The method according to claim 1, wherein a coverage percentage of the surface s derived as the at least one dotting parameter value.

10. The method according to claim 1, wherein the at least one dotting parameter is derived for a plurality of different process parameter values.

11. The method according to claim 1, wherein deriving the dotting parameter value comprises calculating an averaged dotting parameter value being averaged over an averaging time domain.

12. The method according to claim 1, wherein deriving the dotting parameter value comprises calculating an averaged dotting parameter value, the averaging time domain being a later half of the time interval, a middle portion of 75% of the time interval or a middle portion of 80% of the time interval.

13. The method according to claim 1, wherein the derived at least one dotting parameter value is used as an input and/or as a verification means for a numeric simulation.

14. The method according to claim 1, being executed by a processor executing a program code implementing the method.

15. A computer program product for assessing a dotting of a surface, 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

[0029] FIG. 1 schematically shows a schematic illustration of a lateral view of a dotting assessment configuration for carrying out a method according to a first embodiment of the invention;

[0030] FIG. 2 shows an image of a dotted surface, the image being captured early in the time interval;

[0031] FIG. 3 shows an image of the dotted surface, the image being captured late in the time interval;

[0032] FIG. 4 shows a flowchart of a step of image processing according to the first embodiment of the invention;

[0033] FIG. 5 shows a graph of a derived first dotting parameter value and a first averaging time domain;

[0034] FIG. 6 shows a graph of a derived second dotting parameter value and a second averaging time domain;

[0035] FIG. 7 shows a graph of a derived third dotting parameter value and a third averaging time domain;

[0036] FIG. 8 shows a graph of averaged first dotting parameter values for a first liquid and different process parameter values;

[0037] FIG. 9 shows a graph of averaged first dotting parameter values for a second liquid and different process parameter values;

[0038] FIG. 10 shows a graph of averaged second dotting parameter values for the first liquid and different process parameter values;

[0039] FIG. 11 shows a graph of averaged second dotting parameter values for the second liquid and different process parameter values;

[0040] FIG. 12 shows an image of a dotted surface, the image being captured in a method according to a second embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0041] FIG. 1 schematically shows a schematic illustration of a lateral view of a surface dotting assessment configuration 1 for carrying out a method according to a first embodiment of the invention. The surface dotting configuration comprises a liquid spray configuration with a conical spray nozzle 10 for delivering a liquid spray 11. The surface dotting assessment 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 surface dotting assessment configuration comprises a surface 12 to be dotted which is provided as a transparent pane or the like and a high-speed camera (not shown) which is arranged opposite to the spray nozzle 10 with respect to the surface 12. The high-speed camera is oriented such that an optical axis of the high-speed camera extends towards the spray nozzle 10. The surface dotting assessment configuration may be used to assess a dotting of the surface 12.

[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 dotting of the surface 12 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 dotting of the surface 12 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 for receiving one or more captured images 20, 22, 120 (see FIGS. 2, 3, 12) from the high-speed camera.

[0044] The surface dotting assessment configuration is configured for carrying out a method for assessing a dotting of the surface 12 according to the invention. The method comprises the following steps.

[0045] A liquid is fed to the spray nozzle 10 at a feeding rate and the spray nozzle 10 is rotated at an angular speed during a predetermined interval of time which is chosen to have 250 milliseconds (ms). Due to the operation of the spray nozzle 10 the surface 12 is gradually dotted by droplets of a liquid spray 11 delivered by the spray nozzle 10. Dotting the surface 12 comprises covering the surface 12 with a plurality of droplets each droplet creating a dot on the surface.

[0046] A plurality of images 20, 22, 122 of the dotted surface 12 is captured during the predetermined time interval.

[0047] FIG. 2 shows an image 20 of the dotted surface 12 which has been captured early in the time interval.

[0048] FIG. 3 shows an image 22 of the dotted surface 12 which has been captured late in the time interval.

[0049] The plurality of images 20, 22, 122 is successively processed. Processing an image 20, 22, 122 comprises pre-processing the captured image 20, 22, 122 by means of ordinary image processing, i.e. modifiying a contrast, a brightness, a sharpness, a color saturation and the like of the image 20, 22, 122, and converting the pre-processed image into a binary image 30, 31.

[0050] FIG. 4 shows a flowchart of a step of image processing according to the first embodiment of the invention.

[0051] The pre-processed image is converted both into a first binary image 30 using a first higher sensitivity and into a second binary image 31 using a second lower sensitivity.

[0052] In a further step at least one dotting parameter value 43, 53, 63, 73, 83, 93, 103 is derived from the processed plurality of images 30, 31, wherein a first dotting parameter value derived from the first binary image 30 and a second dotting parameter value derived from the second binary image 31 are combined to a combined dotting parameter value 32 representing the at least one dotting parameter value 43, 53, 63, 73, 83, 93, 103.

[0053] Successively processing the plurality of images 20, 22, 122 comprises stopping processing when a number of dots 21, 23, 121 in the second binary image 31 is larger than a number of dots 21, 23, 121 in the first binary image 30.

[0054] A number of dots 21, 23, 121 or a number of small dots 21, 23, 121 is derived as a first dotting parameter value 43.

[0055] FIG. 5 shows a graph 40 of the derived first dotting parameter value 43 and a first averaging time domain 44. The graph 40 has an abscissa 41 indicating a time in a range from 0 ms to 250 ms and an ordinate 42 indicating a number of dots 21, 23, 121 in a range from 0 to 6.000. The number of dots 21, 23, 121 is plotted as the first dotting parameter 43 dependent on the time. Apart from that, the later half of the time range defining the time interval is plotted as a first averaging time domain 44.

[0056] An average dot diameter is derived as a second dotting parameter value 53.

[0057] FIG. 6 shows a graph 50 of the derived second dotting parameter value 53 and a second averaging time domain 54. The graph 50 has an abscissa 51 indicating a time in a range from 0 milliseconds (ms) to 250 ms and an ordinate 52 indicating an average dot diameter in a range from 60 micrometer (μm) to 130 μm. The average dot diameter is plotted as the second dotting parameter 53 dependent on the time. Apart from that, a middle portion of 75% of the time range defining the time interval is plotted as a second averaging time domain 54.

[0058] A coverage percentage of the surface 12 is derived as a third dotting parameter value 63.

[0059] FIG. 7 shows a graph 60 of the derived third dotting parameter value 63 and a third averaging time domain 64. The graph 60 has an abscissa 61 indicating a time in a range from 0 milliseconds (ms) to 250 ms and an ordinate 62 indicating a coverage percentage of the surface in a range from 0 per cent (%) to 25%. The coverage percentage is plotted as the third dotting parameter 63 dependent on the time. Apart from that, a middle portion of 80% of the time range defining the time interval is plotted as a third averaging time domain 64.

[0060] Deriving the dotting parameter value may comprise calculating an averaged dotting parameter value 73, 83, 93, 103 (see FIGS. 8, 9, 10, 11) over an averaging time domain 44, 54, 64. The averaging time domain 44, 54, 64 may be a later half of the time interval, a middle portion of 75% of the time interval or a middle portion of 80% of the time interval, respectively. Furthermore, each dotting parameter value 73, 83, 93, 103 may be derived for a plurality of different process parameter values 110, 111, 112, 113, 114, 115, 116, 117.

[0061] FIG. 8 shows a graph 70 of averaged first dotting parameter values 73 for a first liquid and different process parameter values 110, 114, 117. The graph 70 has an abscissa 71 indicating an angular speed of the spray nozzle 11 in a range from 10.000 rotations per minute (rpm) to 35.000 rpm and an ordinate 72 indicating an averaged number of dots 21, 23, 121 in a range from 4.600 to 7.800 for an acrylate as the first liquid. The averaged number of dots 21, 23, 121 is plotted as the averaged first dotting parameter value 73 for three different feeding rates each representing a process parameter value 110, 114, 117 of 50 milliliter per minute (ml/min), 150 ml/min and 250 ml/min, respectively. The averaged first dotting parameter value 73 increases with an increasing angular speed of the spray nozzle 10. The effect of the feeding rate 110, 114, 117 on the averaged first dotting parameter value 73 varies substantially dependent on the angular speed of the spray nozzle 10.

[0062] FIG. 9 shows a graph 80 of averaged first dotting parameter values 83 for a second liquid and different process parameter values 110, 111, 112, 113, 114, 115, 116, 117. The graph 80 has an abscissa 81 indicating a angular speed of the spray nozzle 11 in a range from 10.000 rotations per minute (rpm) to 35.000 rpm and an ordinate 82 indicating an averaged number of dots 21, 23, 121 in a range from 1.000 to 2.800 for an oil as the second liquid. The averaged number of dots 21, 23, 121 is plotted as the averaged first dotting parameter value 83 for eight different feeding rates each representing a process parameter value 110, 111, 112, 113, 114, 115, 116, 117 of 50 ml/min, 75 ml/min, 100 ml/min, 125 ml/min, 150 ml/min, 175 ml/min, 200 ml/min and 250 ml/min, respectively. The averaged first dotting parameter value 83 increases with an increasing angular speed of the spray nozzle 10. The effect of the feeding rate 110, 111, 112, 113, 114, 115, 116, 117 on the averaged first dotting parameter value 83 varies substantially dependent on the angular speed of the spray nozzle 10.

[0063] FIG. 10 shows a graph of averaged second dotting parameter values 93 for the first liquid and different process parameter values 110, 114, 117. The graph 90 has an abscissa 91 indicating an angular speed of the spray nozzle 11 in a range from 20.000 rotations per minute (rpm) to 35.000 rpm and an ordinate 92 indicating an averaged average dot diameter in a range from 58 μm to 70 μm for an acrylate as the first liquid. The averaged average dot diameter is plotted as the averaged second dotting parameter value 93 for three different feeding rates of the first liquid each representing a process parameter value 110, 114, 117 of 50 milliliter per minute (ml/min), 150 ml/min and 250 ml/min, respectively. The averaged second dotting parameter value 93 decreases with an increasing angular speed of the spray nozzle 10. The effect of the feeding rate 110, 114, 117 on the averaged second dotting parameter value 93 varies substantially dependent on the angular speed of the spray nozzle 10.

[0064] FIG. 11 shows a graph of averaged second dotting parameter values 103 for the second liquid and different process parameter values 110, 111, 112, 113, 114, 115, 116, 117. The graph 100 has an abscissa 101 indicating an angular speed of the spray nozzle 11 in a range from 10.000 rotations per minute (rpm) to 35.000 rpm and an ordinate 102 indicating an averaged average dot diameter in a range from 46 to 70 for an oil as the second liquid. The averaged average dot diameter is plotted as the averaged second dotting parameter value 103 for eight different feeding rates each representing a process parameter value 110, 111, 112, 113, 114, 115, 116, 117 of 50 ml/min, 75 ml/min, 100 ml/min, 125 ml/min, 150 ml/min, 175 ml/min, 200 ml/min and 250 ml/min, respectively. The averaged second dotting parameter value 103 increases with an increasing angular speed of the spray nozzle 10. The effect of the feeding rate 110, 111, 112, 113, 114, 115, 116, 117 on the averaged second dotting parameter value 103 varies substantially dependent on the angular speed of the spray nozzle 10.

[0065] The substantial variations of the derived first and second averaged dotting parameter values 73, 83, 93, 103 dependent on the angular speed of the spray nozzle 10 and differences related to the liquid sprayed by the nozzle 10 may be theoretically traced back to a plurality of dimensionless numbers which comprise a ratio of the respective viscosities, a ration of the respective surface tensions, a ratio of the centrifugal forces, a Reynolds number, a Weber number, a capillary number, a Laplace number and the like.

[0066] The derived at least one dotting parameter value 43, 53, 63, 73, 83, 93, 103 may be used as an input and/or as a verification means for a numeric simulation.

[0067] FIG. 12 shows an image 120 of a dotted surface 12, the image 120 being captured in a method according to a second embodiment of the invention. The image 120 comprises a plurality of dots 121 and shows a coated surface 12 which has been chipped by a plurality of projectiles, i.e. stones and the like, during an interval of time. Comparing the image 120 with the image 20 shown in FIG. 2 results in the insight that chipping and spraying may be assessed in the same way.

REFERENCE NUMERALS

[0068] 1 surface dotting assessment configuration

[0069] 10 spray nozzle

[0070] 11 liquid spray

[0071] 12 surface

[0072] 20 image, captured early

[0073] 21 dot

[0074] 22 image, captured late

[0075] 23 dot

[0076] 30 binary image, higher sensitivity

[0077] 31 binary image, lower sensitivity

[0078] 32 combined dotting parameter value

[0079] 40 graph

[0080] 41 abscissa

[0081] 42 ordinate

[0082] 43 first dotting parameter value

[0083] 44 first averaging time domain

[0084] 50 graph

[0085] 51 abscissa

[0086] 52 ordinate

[0087] 53 second dotting parameter value

[0088] 54 second averaging time domain

[0089] 60 graph

[0090] 61 abscissa

[0091] 62 ordinate

[0092] 63 third dotting parameter value

[0093] 64 third averaging time domain

[0094] 70 graph

[0095] 71 abscissa

[0096] 72 ordinate

[0097] 73 averaged first dotting parameter value for a first liquid

[0098] 80 graph

[0099] 81 abscissa

[0100] 82 ordinate

[0101] 83 averaged first dotting parameter value for a second liquid

[0102] 90 graph

[0103] 91 abscissa

[0104] 92 ordinate

[0105] 93 averaged second dotting parameter value for the first liquid

[0106] 100 graph

[0107] 101 abscissa

[0108] 102 ordinate

[0109] 103 averaged second dotting parameter value for the second liquid

[0110] 110 process parameter value

[0111] 111 process parameter value

[0112] 112 process parameter value

[0113] 113 process parameter value

[0114] 114 process parameter value

[0115] 115 process parameter value

[0116] 116 process parameter value

[0117] 117 process parameter value

[0118] 120 image

[0119] 121 dot