METHOD FOR LASER ENGRAVING ON CLOTHING AND CORRESPONDING MACHINE

Abstract

A method for laser engraving on clothing and to a corresponding machine. Using an image, a laser burns, for each pixel, a corresponding point on the clothing, with a laser energy level that is a function of the pixel value. This function has a first zone with a first average gradient and a second zone with a second average gradient. The first zone corresponds to laser energy values less than the second zone, the absolute value of the second average gradient being greater than the absolute value of the first average gradient. The laser engraving machine comprises a laser source, means for conducting the laser on specific points of the clothing, means for controlling the energy supplied by the laser, and control means configured to carry out the method.

Claims

1-15. (canceled)

16. Method for laser engraving of clothing, comprising: starting with a digital image, in which each pixel of the image has a pixel value comprised between a minimum pixel value and a maximum pixel value, and in which for each pixel a laser burns a point in said clothing corresponding to said pixel, with a laser energy level which is a function of said pixel value, wherein said function has a first region with a first mean gradient and a second region with a second mean gradient, in which said first region corresponds to lower laser energy values than said second region; and the absolute value of said second mean gradient is higher than the absolute value of said first mean gradient.

17. Method according to claim 16, wherein a point of change defining the transition between said first region and said second region is determined between 40% and 60% of the maximum pixel value.

18. Method according to claim 16, wherein said second region has a first section with a third mean gradient; and a second section with a fourth mean gradient, wherein said second section corresponds to higher laser energy values than said first section, and wherein the absolute value of said fourth mean gradient is lower than the absolute value of said third mean gradient.

19. Method according to claim 18, wherein the transition between said first section and said second section lies between 20% and 35% of the maximum pixel value if said function is monotonically decreasing, or between 65% and 80% of the maximum pixel value if said function is monotonically increasing.

20. Method according to claim 16, further comprising it is determined a cut-off point defining a transition between said first region and a third region, in which the energy value is zero, and said cut-off point lies between 82% and 90% of the maximum pixel value if said function is monotonically decreasing, or between 10% and 18% of the maximum pixel value if the function is monotonically increasing.

21. Method according to claim 16, wherein said minimum pixel value is 0 and said maximum pixel value is 255, said function being monotonically decreasing, in which in said first region the gradient has a variation lower than 5%, said function being a linear function in said first region.

22. Method according to claim 17, wherein said function has the following form: for said first region, $E=E_{\max }.Math.\frac{V_{\max }-p}{V_{\max }}$ for said second region, $E=E_{\max }\left(\frac{V_{\max }-p}{V_{\max }}\right).Math.\left(1+H\left(1+\tan .Math..Math.h\left(2-C.Math.\frac{p}{V_T}\right)\right)\right)$ where: E, represents the energy level of the laser for the point, E.sub.max, represents the maximum energy value of the linear contribution, V.sub.max, represents the maximum pixel value, preferably 255, p, represents the pixel value for the point, being p[0; V.sub.max], V.sub.T represents said point of change between said first region and said second region, H represents a factor controlling the hyperbolic contribution having a value in the range of 1/3 to 5/3, and C represents a constant controlling the hyperbolic gradient.

23. Method according to claim 22, wherein said factor controlling the hyperbolic contribution, H, has the following formula: $H=\frac{1}{A-B.Math.F}$ where: A and B represent constants, and F is a predetermined parameter controlling the amount of contribution to the effect and having a value comprised between 1 and 100.

24. Method according to claim 23, wherein A has a value of 499/165, B has a value of 4/165, and F has a value between 0 and 100; and when F has a value 0, the same linear formula is used in said second region as for said first region.

25. Method according to claim 22, wherein said factor controlling the hyperbolic contribution, H, has the following formula:
H=a.Math.F+b where: a and b represent constants, and F is a predetermined parameter controlling the amount of contribution to the effect and having a value comprised between 1 and 100.

26. Method according to claim 25, wherein a has a value of 4/297, b has a value of 95/297, and F has a value between 0 and 100; and when F has a value 0, the same linear formula is used in said second region as for said first region.

27. Method according to claim 16, wherein said laser emits pulses of light having a maximum pulse power, and in which said energy level for each point is obtained by varying at least one parameter among the list of parameters consisting of: maximum power, number of pulses and duration of said pulses.

28. Method according to claim 27, wherein said energy level has the following formula:
E=D.Math.P.sub.max.Math.T.sub.E where: E, represents the energy level, D, represents the duty cycle of the laser, defined as the time fraction in which the laser emits light vs the total exposure time, T.sub.E, P.sub.max, represents the maximum power of laser pulses, and T.sub.E, represents the exposure time, being the total time, in which the laser emits at least one light pulse on the point.

29. Laser engraving machine for clothing, comprising: a laser source; conducting means, for conducting the light emitted by said laser source to specific points of said clothing; energy controlling means, for controlling the energy provided by said laser; and control means, configured to control said conducting means and said energy controlling means for engraving said clothing, said control means having an energy determination module for determining a laser energy level for each of said points of said clothing; wherein said energy determination module is configured to use a digital image, in which each pixel of the image has a pixel value, comprised between a minimum pixel value and a maximum pixel value, in which each pixel corresponds to one of said points of said clothing, and determine said laser energy level for each of said points of said clothing as a function of said pixel value in the corresponding pixel of the image; wherein said function has a first region with a first mean gradient and a second region with a second mean gradient, in which said first region corresponds to lower laser energy values than said second region; and the absolute value of said second mean gradient is higher than the absolute value of said first mean gradient.

30. Machine according to claim 29, further comprising user parameter input means comprising at least one of the parameters: the point of change between said first region and said second region; the amount of contribution to the effect, being a value comprised between 0 and 100, in which a value 0 indicates that a linear function is used in said second region, and higher values indicate an increasingly stronger contribution of a nonlinear component to said second region; and the cut-off point between said first region and said third region; and wherein said energy determination module is further configured to use said at least one parameter to determine said function.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0067] The advantages and characteristics of the invention will be more apparent from the following description which, without limiting main claim, explains certain preferred embodiments of the invention, referring to the figures.

[0068] FIG. 1A and FIG. 1B show an example of laser engraving. FIG. 1A shows a conventional image having a flat appearance, while FIG. 1B shows the same example of laser engraving in which the 3D effect is observed.

[0069] FIGS. 2A and 2B show an example of design images for double marking. FIG. 2A shows the first basic image, while FIG. 2B shows the second image with regions to be emphasized.

[0070] FIG. 3 shows a sample function for one simplified embodiment of the invention.

[0071] FIG. 4A to 4C show functions for an example of embodiment of the invention, for different values of the parameter F.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0072] FIG. 1A shows an example of engraving on denim clothing, simulating a natural wear. The result obtained has a very flat appearance. FIG. 1B shows the same type of engraving but with the so-called 3D effect. The prior art known for achieving this effect is based on double marking, such that two images are designed which need to be engraved in two passes of the laser so as to be superimposed on and aligned with each other. Thus, in the double marking technique, it is used a first image 101, shown in FIG. 2A, with the general design, and a second image 102, shown in FIG. 2B, with the regions to be highlighted. Note that the images used in FIGS. 2A and 2B are in fact a negative representation wherein the darker pixels correspond to higher laser energy values, and therefore to lighter values in the final result on the clothing.

[0073] In order to overcome the drawbacks of the prior art, in one embodiment of the invention shown in FIG. 3 the method for laser engraving of clothing starts with a single digital image 101, comprising pixels with a minimum value of 0 and a maximum value of 255. For each of the pixels of the image 101, a laser burns a corresponding point in the clothing with an energy which is a function of the pixel value. In the case of the examples, the function is monotonically decreasing, such that low pixel values correspond to high lights on the clothing and vice versa. Thus, for the case of the example, the function has three differentiated regions, with a first linear region 1 which is equivalent to what would have been obtained in the current prior art. For reference, FIG. 3 shows by a slanting broken line the reference with regard to the prior art. This same line is shown in FIG. 4A to 4D. For the sake of clarity, and in order to easily understand the relations between the different energies, the maximum energy of the linear component, which would correspond to the current prior art has been normalized to 1 in the figures.

[0074] In the case of the example shown in FIG. 3, the function also has a second region 2 with a first section 21 and a second section 22. For the sake of clarity and unless otherwise indicated, when comparing gradients it shall be understood that the absolute value thereof is being compared, not taking into account the sign of the gradient. In the example, the mean gradient of the second region 2 is greater than that of the first region 1. In turn, the gradient of the first section 21 is also greater than that of the second section 22. Finally, the function has a third region 3, where the energy value is zero. The resulting function is monotonically decreasing. Thus, the order of the regions from more to less energy of the laser is: second section 22 of the second region 2, first section 21 of the second region 2, first region 1, third region 3. In the case of the example, except for the third region 3, all sections are linear.

[0075] In FIG. 3, the limits of the different regions have been marked by vertical broken lines. In particular, the point of change 4 defining the transition between the first region 1 and the second region 2 is situated at a pixel value corresponding to 120. In turn, the transition between the first section 21 and the second section 22 corresponds to the pixel value 70. Finally, the cut-off point 5 defining the transition between the first region 1 and the third region 3 is at a pixel value of 230.

[0076] FIG. 4A to 4D show another embodiment of the invention. In this example, the function has the following form: [0077] for said first region (1),

[00004]$E=E_{\max }.Math.\frac{255-p}{255}$ [0078] for said second region (2),

[00005]$E=E_{\max }\left(\frac{255-p}{255}\right).Math.\left(1+H\left(1+\tan .Math..Math.h\left(2-4.Math.\frac{p}{V_T}\right)\right)\right)$

where: [0079] E, represents the energy level of the laser for the point, [0080] E.sub.max, represents the maximum energy value of the linear contribution, [0081] p, represents the pixel value for the point, being p[0; 255], [0082] V.sub.T represents said point of change (4) between said first region (1) and said second region (2), for this example V.sub.T=120 has been chosen. [0083] H represents a factor controlling the hyperbolic contribution, having a range of values between 1/3 and 5/3,

[0084] For this exemplary embodiment, H has the following formula:

[00006]$H=\frac{165}{499-4.Math.F}$

[0085] Where F is a predetermined parameter controlling the amount of contribution to the effect, preferably having a value between 1 and 100, or a value of 0 when using a different formulation. In particular, the method of the example considers that if F=0, the second region 2 uses the same formula as described for the first region 1, so that a linear function results in both regions. In FIG. 4A, it may be observed the particular case of the function when F=0. FIG. 4B shows the case of F=1, FIG. 4C shows the case of F=50, and FIG. 4D shows the case of F=100.

[0086] In another embodiment, H has the following formula:

[00007]$H=\frac{4.Math.F+95}{297}$

[0087] Where F is equivalent to the previous example. The skilled person will understand that, with this example, it is possible to obtain the same graphics as represented in FIG. 4A to 4D, even though the values of F will be different.

[0088] For the embodiments, the machine which performs the engraving comprises a laser light source, with guiding means for the light emitted onto specific points of the clothing where the design is being engraved. It also comprises adequate control means to control the energy being provided by said laser for each point, following the method described above.

[0089] In these embodiments, the machine is able to obtain a spatial resolution of 32 dots per inch, with a dot size of around 1.2 mm. The maximum laser energy which can be transmitted to each point is 6.5 mJ.

[0090] In the examples, the source involved is a pulsed laser, which emits a series of high-frequency pulses for each point of the clothing, each of them having a maximum pulse power, and with a particular duty cycle. In the case of the examples, the total energy being transmitted is obtained by varying the exposure time in which pulses are emitted for said point. Since selecting a specific time is tantamount to selecting the number of pulses fired during that time, the total energy transmitted to the point is controlled by varying the number of pulses fired by the laser for said point. In other examples, the energy is controlled by varying the maximum power, the duration of said pulses, or a combination of the two.

[0091] Thus, the energy level has the following formula:

E=D.Math.P.sub.max.Math.T.sub.E

where: [0092] E, represents the energy level, [0093] D, represents the duty cycle of the laser, [0094] P.sub.max, represents the maximum power of the laser pulses, [0095] T.sub.E, represents the exposure time, being the total time in which the laser is emitting at least one light pulse on the point.

[0096] For the previous examples, the method is parametrizable, so that the machine comprises input means for the following parameters: [0097] the point of change 4 between the first region 1 and the second region 2; [0098] the amount of contribution to the effect, F, being a value between 0 and 100, as previously described; and [0099] the cut-off point 5 between said first region 1 and said third region 3.

[0100] In other examples, the input means make it possible to select among certain predetermined pre-sets: [0101] Soft mode, selecting V.sub.T=120, F=10; corresponding to a more realistic effect between those which the designer sees on the screen and the final result on the clothing; [0102] Medium mode, V.sub.T=120, F=25; being the most common value which potentiates the effect of wear and offers a more natural 3D effect; [0103] Strong mode, V.sub.T=30, F=75; which for the main part of designs highlights the central part of the image, having an optical effect of thinness at the centre; or [0104] Custom mode, where the user may himself choose the values of V.sub.T and F.