SYSTEM AND METHOD FOR LASER MARKING A GRAPHIC ON AN OBJECT

Abstract

A system and a method for laser marking a graphic on an object. The system includes: a laser system for producing a laser output; element(s) for moving the laser output on a surface of an object; a controller for controlling the laser system and the moving element(s), and for processing control information including a plurality of vectors, where for each vector the controller is configured to set a vector speed and a vector laser power according to a marking intensity value of the corresponding vector group such that at least two vectors within one of the vector groups have with respect to each other different vector speeds and vector laser powers, and a laser output's speed that is set according to the at least two vectors remains different than zero when the laser output travels along two trajectory parts which correspond to the at least two vectors.

Claims

1. A system for laser marking a graphic on an object, the system comprising: a laser system for producing a laser output; moving means for moving the laser output for the latter traveling on a surface of an object; and a controller configured for: processing control information associated with a graphic to be laser marked, said control information comprising or concerning a plurality of vectors, the vectors being separable into two or more vector groups, each group having a corresponding marking intensity value, wherein at least one of said groups has a plurality of vectors; for each vector setting a corresponding vector speed and a corresponding vector laser power; controlling the laser system for setting a power of the laser output according to the vector laser power; controlling the moving means for setting on the surface of the object a trajectory and a speed of the laser output according to each vector and the corresponding vector speed, wherein for each vector the trajectory has a corresponding trajectory part, wherein, for each vector the controller is configured to set the vector speed and the vector laser power according to the marking intensity value of the corresponding vector group such that at least two vectors within one of said vector groups have with respect to each other different vector speeds and different vector laser powers, and such that the laser output's speed that is set according to said at least two vectors remains different than zero when the laser output travels along the two trajectory parts which correspond to said at least two vectors.

2. The system for laser marking a graphic according to claim 1, wherein the controller is further configured to set the trajectory according to a series of the vector groups, said series comprising a particular vector group and a subsequent vector group that follows the particular vector group in said series, and the particular and the subsequent vector groups having different with respect to each other marking intensity values, wherein at least two vectors in the particular vector group and at least one or two vectors in the subsequent vector group form a subseries and have with respect to each other different vector speeds and/or different vector laser powers, and the controller being configured for setting said different vector speeds and/or different vector laser powers such that in said subseries the vector speeds change monotonically, and/or such that in said subseries the vector laser powers change monotonically.

3. The system for laser marking a graphic according to claim 1, wherein the laser output is pulsed and, for controlling the power of the laser output, the laser system is configured for changing a duty cycle of the laser system.

4. The system for laser marking a graphic according to claim 1, wherein the vector speed depends on a length of the trajectory part that corresponds to the vector, an exposition time that corresponds to duration of the laser output irradiating the object's surface while said laser output travelling across said trajectory part, a maximum marking intensity value that the marking intensity value (MI) of the corresponding vector group can acquire, and a correction factor which is related to the laser system, according to the formula: $v_i=\frac{D}{t_E}*\frac{FS}{FS-\mathrm{MI}}*LEQi$

5. The system for laser marking a graphic according to claim 1, further comprising a computer configured for converting a raster graphic into the control information.

6. The system for laser marking a graphic according to claim 1, wherein the marking intensity value is in a scale that has a maximum marking intensity value and a minimum marking intensity value, said scale being a color grayscale that has FS=255 and FM=0.

7. The system for laser marking a graphic according to claim 1, wherein the controller is configured to set the vector speed to be equal to or smaller than a maximum speed, and wherein when at least one of the vectors the corresponding vector speed is about equal to said maximum speed, the controller is configured to further control the laser system for correcting the power of the laser output.

8. The system for laser marking a graphic according to claim 1, wherein for at least one of the vectors, the corresponding vector speed is larger than a maximum speed, the controller is configured to further control the laser system for correcting the power of the laser output.

9. The system for laser marking a graphic according to claim 1, wherein the laser output is pulsed comprising a number of pulses per vector, said number being 1 or higher, and the laser system which produces the pulsed optical output is configured to change the number of pulses per vector.

10. A method for laser marking a graphic on an object, the method comprising: producing a laser output by means of a laser system; moving the laser output using moving means such that the laser output travels on a surface of an object; processing control information associated with a vector graphic to be laser marked, said control information comprising a plurality of vectors, the vectors being separable into two or more vector groups, each group having a corresponding marking intensity value, wherein at least one of said groups has a plurality of vectors; for each vector setting a corresponding vector speed and a corresponding vector laser power; controlling the laser system for setting a power of the laser output according to the vector laser power; and controlling the moving means for setting, on the surface of the object, a trajectory and a speed of the laser output according to each vector and the corresponding vector speed, wherein for each vector the trajectory has a corresponding trajectory part, wherein, for each vector setting the vector speed and the vector laser power according to the marking intensity value of the corresponding vector group such that at least two vectors within one of said vector groups have with respect to each other different vector speeds and different vector laser powers, and the laser output's speed that is set according to said at least two vectors remains different than zero when the laser output travels along the two trajectory parts which correspond to said at least two vectors.

11. The method for laser marking a graphic on an object according to claim 10, wherein the object comprises a denim fabric.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 shows a preferred embodiment of the system according to the invention.

[0038] FIG. 2 shows an example of a graphic that can be marked according to the invention; the graphic in FIG. 2 is a line comprising three segments of different gray levels.

[0039] FIG. 3 shows a typical CO.sub.2 laser response.

[0040] FIG. 4 shows non-limiting examples of how the power of the laser output may be modified in an embodiment according to the invention.

[0041] FIG. 5 shows a non-limiting example of a laser output scanning for a vectorial image marking done according to the present invention, and an example of a traditional raster marking done line-by-line.

DETAILED DESCRIPTION

[0042] FIG. 1 schematically shows a preferred embodiment of the system according to the first aspect of the invention. The system in FIG. 1 comprises a laser system 1 for producing a laser output, moving means 21 which in this case comprises a pair of galvo scanning mirrors 21 for moving (scanning) the laser output on a surface of an object 3. In the system of FIG. 1 the laser output is a laser beam. In a preferred embodiment where the object is a textile, during the marking process the optical output impinges (hits) on and scans over the surface of the textile 3. The optical output traveling from the laser system towards the surface of the object is indicated by the thick arrows in FIG. 1. In addition, the system of FIG. 1 comprises an electronic controller 22 that is connected to (the connections are schematically indicated in FIG. 1 with dotted lines) and configured to control the laser system 1 and the galvo scanning mirrors 21. In the system of FIG. 1 the controller 22 is connected to a computer (not shown) in which the user may create or insert a digital file that contains control information associated with a graphic to be laser marked, said control information comprising or defining a plurality of vectors, the vectors being separable into two or more vector groups, each group having a corresponding marking intensity value (MI), wherein at least one of said groups has a plurality of vectors. Preferably said digital file may be an image/drawing/pattern/indicia/graphic to be marked on the textile, said image/drawing/pattern/indicia/graphic being vector based. The controller 22 is configured for processing said control information. Therefore, in the preferred embodiment of FIG. 1 the control information is passed from the computer to the controller 22 which is further configured for the following: for each vector the controller 22 sets a corresponding vector speed v.sub.i and a corresponding vector laser power; the controller 22 controls the laser system 1 for setting a power of the laser output according to the vector laser power; the controllers controls the moving means 21 for setting on the surface of the object a trajectory and a speed of the laser output according to each vector and the corresponding vector speed v.sub.i, wherein for each vector the trajectory has a corresponding trajectory part.

[0043] A non-limiting example of the operation of the controller of the system of FIG. 1 is presented below, starting with Table 1 which shows that the control information related to a non-limiting example of a graphic to be marked comprises 3 vector groups, wherein the graphic is a line LN consisting of three differently colored line segments LS1-LS3 as shown in FIG. 2. The color of said line segments is measured in a grayscale from 0 to 4, and in the shown example each of the vector groups of Table 1 has a corresponding grayscale value which corresponds to the corresponding vector group's marking intensity value.

TABLE-US-00001 TABLE 1 Vector Marking Grey Scale Group Intensity [0 to 4] 1 1 1 2 3 3 3 2 2

[0044] In the example of Table 1 and FIG. 2, the controller calculates the laser beam movement speed of each vector, meaning that the controller sets the vector speed for each vector. In the same example, the vector speed depends on the colour or grey scale level of the line segment of each group and the desired maximum marking intensity set by the user.

[0045] Each of the vector groups of Table 1 comprise at least one vector, and at least one of the vector groups comprises two or more vectors. Each vector of the vector groups has a corresponding vector distance (Vec. Distance) which is the length of the vector on the surface on which the graphic is to be marked. Preferably all the vectors of the vector groups have the same vector distance. The vector distance is typically measured or expressed in millimetres. In the optional and preferable case that the vector distance is the same for all vectors, the vector distance depends on the resolution of the marking, wherein said resolution is the number of vectors per unit length. Hence, preferably the vector distance is correlated with the resolution via the following relationship:

[00001]$\begin{array}{cc}\mathrm{Vec}.\mathrm{Distance}\left(\mathrm{mm}\right)=\frac{25,4\left[\frac{\mathrm{mm}}{\mathrm{inch}}\right]}{\mathrm{Resolution}\left[\frac{\mathrm{pixels}}{\mathrm{inch}}\right]},& \mathrm{Equation}2.\end{array}$

[0046] Preferably the vector speed v.sub.i for a vector i marked with the system of FIG. 1 according to the example related to Table 1, is determined according to the formula:

[00002]$\begin{array}{cc}\mathrm{VectorSpeed}\left(i\right)\left[\frac{\mathrm{mm}}{s}\right]=\frac{\mathrm{Vec}.\mathrm{Distance}\left(\mathrm{mm}\right)}{\mathrm{Exposition}\mathrm{Time}\left(s\right)}\star \frac{\mathrm{FS}}{\mathrm{FS}-\mathrm{GreyScaleLevel}\left(i\right)}\star \mathrm{LaserEQ}\left(i\right),& \mathrm{Equation}3\end{array}$

[0047] Equation 3 in view of equation 2 may become:

[00003]$\begin{array}{cc}\mathrm{VectorSpeed}\left(i\right)\left[\frac{\mathrm{mm}}{s}\right]=\frac{\frac{25,4\left[\frac{\mathrm{mm}}{\mathrm{inch}}\right]}{\mathrm{Resolution}\left[\frac{\mathrm{pixels}}{\mathrm{inch}}\right]}}{\mathrm{ExpositionTime}\left(s\right)}*\frac{\mathrm{FS}}{\mathrm{FS}-\mathrm{GreyScaleLevel}\left(i\right)}*\mathrm{LaserEQ}\left(i\right),& \mathrm{Equation}4\end{array}$

[0048] In equations 3 and 4 the exposition time corresponds to the duration of the laser output irradiating the object's surface while said laser output travels across the trajectory part that corresponds to the vector i on the surface of the object; hence the trajectory part has a length that is equal to the vector distance. Also, in equations 3 and 4 FS is the maximum grayscale colour value that a grayscale level of the vector may acquire in the aforementioned example related to table 1. In the herein described example, the grayscale level for vector i can be considered as expressing the marking intensity MI of the vector group in which vector i belongs. LaserEQ(i) in equations 3 and 4 is a correction factor to adjust the relation between the Laser Emission Time and the emitted laser power. It is often, but not always, required to consider the laser equalization correction factor LaserEQ(i) because often the laser power is not linearly dependent on the laser emission time, in which case for each grey scale value a correction factor is preferably used. A typical CO.sub.2 laser response is showed in FIG. 3.

[0049] In the optional and preferred case of working with grayscale graphics using a colour scale that has 255 grey scale levels, i.e. when FS=255 because the grayscale value may be from 0 to 255, then equation 4 becomes:

[00004]$\begin{array}{cc}\mathrm{VectorSpeed}\left(i\right)\left[\frac{\mathrm{mm}}{s}\right]=\frac{\mathrm{Vec}.\mathrm{Distance}\left(\mathrm{mm}\right)}{\mathrm{ExpositionTime}\left(s\right)}\star \frac{255}{255-\mathrm{GreyScaleLevel}\left(i\right)}\star \mathrm{LaserEQ}\left(i\right)=\frac{\frac{25,4\left[\frac{\mathrm{mm}}{\mathrm{inch}}\right]}{\mathrm{Resolution}\left[\frac{\mathrm{pixels}}{\mathrm{inch}}\right]}}{\mathrm{ExpositionTime}\left(s\right)}\star \frac{\mathrm{FS}}{\mathrm{FS}-\mathrm{GreyScaleLevel}\left(i\right)}\star \mathrm{LaserEQ}\left(i\right),& \mathrm{equation}5.\end{array}$

[0050] Expressing the vector speed as v.sub.i, the vector distance as D which is the length of the trajectory part that corresponds to the vector, the exposition time as t.sub.E that corresponds to duration of the laser output irradiating the object's surface while said laser output travelling across said trajectory part, as well as considering that FS is a maximum marking intensity value that the marking intensity value MI of the corresponding vector group can acquire, and expressing the laser correction factor as LEQi, then from equation 6 it can be derived that in the embodiment of FIG. 1 the vector speed is set according to the aforementioned equation 1:

[00005]$v_i=\frac{D}{t_E}*\frac{FS}{FS-\mathrm{MI}}*LEQi$

[0051] Hence, the vector speed v.sub.i may acquire different values depending on the marking intensity MI value of the vector's vector group. In the previous example related to Table 1, the vector speed may vary between a high value, a medium value and a low value, as shown in Table 2:

TABLE-US-00002 TABLE 2 Vector Marking Vector Group Intensity Speed 1 1 High 2 3 Low 3 2 Medium

[0052] Preferably after the speed in each vector is set, then the laser ON and OFF times are calculated for each vector; this calculation is very useful for the embodiment of FIG. 1 because the mirrors that moves the laser beam may have a maximum speed, and is possible that a speed that is calculated only on the basis of equation 1 will be out of the possible range of the mirrors and of the overall hardware of the system. Hence, a preferred calculation method is the following:

[00006]$\begin{array}{cc}\mathrm{If}\mathrm{Speed}\left(\mathrm{vector}\right)<\mathrm{Maximum}\mathrm{Speed};\mathrm{then}:\mathrm{Laser}\mathrm{OffTime}\left(\mathrm{vector}\right)=0,\mathrm{and},\mathrm{If}\mathrm{Speed}\left(\mathrm{vector}\right)>\mathrm{Maximum}\mathrm{Speed};\mathrm{then}:\mathrm{Laser}\mathrm{OffTime}\left(\mathrm{vector}\right)=\frac{\mathrm{Distance}}{\mathrm{Maximum}\mathrm{Speed}}-\frac{\mathrm{Distance}}{\mathrm{Speed}\left(\mathrm{vector}\right)},& \mathrm{Equation}6\end{array}$

[0053] This above means that if the maximum speed is lower than the vector speed that is calculated according to any of equation 1, 3-5, then as the laser beam will move at its maximum speed without being able to go any faster, this will increase the real exposition time in the vector, and to compensate the laser will be off during a period of time, called above LaserOffTime, in order to maintain the original exposition time and keep this way the delivery of energy in that vector.

[0054] When optionally the laser output is pulsed, i.e. comprises laser pulses, then to prevent marking defects the laser off time can be divided (i.e. distributed) between the different laser pulses during the vector.

[0055] Therefore, in the embodiment of FIG. 1 if the vector speed v.sub.i is larger than a maximum speed v.sub.max, then the controller is configured to further control the laser system for correcting the power of the laser output. Similarly, in an embodiment of the system according to the present invention the controller sets the vector speed v.sub.i to be equal to or smaller than a maximum speed v.sub.max, and when for at least one of the vectors the corresponding vector speed v.sub.i is about equal to said maximum speed v.sub.max, the controller is configured to further control the laser system for correcting the power of the laser output.

[0056] Once the real laser beam speed is set, e.g. is calculated, then preferably a next step followed by the controller is calculating the acceleration of the laser beam. This calculation may be very useful in the system of FIG. 1 because galvo mirrors that move the laser beam may have a maximum capacity of acceleration, so it may not be possible to do changes of speed with zero transition time. It is noted that the acceleration may happen at the same time in two axes of the laser beam movement.

[0057] Usually, the time required for the laser beam to change the speed is called “acceleration time”; in some galvanometer-based systems that may be used in an embodiment of the present invention the acceleration time is constant for most of the speed changes and depends on the defined “Tracking Error” as follows:

Acceleration Time[s]=2*Tracking Error[s],  equation 7.

[0058] In equation 7 the acceleration time and the tracking error as measured in seconds (s).

[0059] Preferably to keep the control of the position and speed of the laser beam the controller updates the position of the laser beam in a cycle time/period usually of 10 μs, this period could be higher or lower depending on the performance of the actual controller. Each of these small steps of position may be called “Microvector” or “Acceleration microvector”. A microvector (acceleration microvector) is a vector.

[0060] As the acceleration time is preferably known before reaching a transition point between two vectors, the speed of the laser beam preferably is gradually modified during the transitions by reducing or increasing the speed as may be required.

[0061] The number of microvectors, said vectors also called “acceleration microvectors”, that may be needed to do a change of speed is preferably determined by the following equation:

[00007]$\begin{array}{cc}\mathrm{Acceleration}\mathrm{Microvectors}=\frac{2*\mathrm{Tracking}\mathrm{Error}\left[s\right]}{\mathrm{Micr}ove\mathrm{ctor}\mathrm{Duration}\left[s\right]},& \mathrm{equation}8.\end{array}$

[0062] Optionally and preferably the microvector duration is constant, and further preferably is 10 μs, in which case equation 8 becomes:

[00008]$\begin{array}{cc}\mathrm{Acceleration}\mathrm{Microvectors}=\frac{2*\mathrm{Tracking}\mathrm{Error}\left[s\right]}{10\mu s},& \mathrm{equation}9.\end{array}$

[0063] When having a set of several acceleration microvectors for achieving a change in speed between two consecutive vector groups which belong to a series of vector groups, then preferably an acceleration microvector of the set may belong to a first or current vector group of said two consecutive vector groups, and one or more subsequent acceleration microvectors of the set may be at the beginning of the next or subsequent vector group of the two vector groups. Said set of the several acceleration microvectors for achieving the change in speed between the two consecutive vector groups, is essentially a subseries of vectors that belongs to the series of all the vectors of the corresponding vector group series. The proportion in which the acceleration microvectors of the subseries may be distributed between the two vector groups of the series may vary; according to tests done by the inventors, the best compromise between marking quality and performance is achieved when 50-70% of the subseries's acceleration microvectors belong in one of the first (current) or the second (next or subsequent) vector group, and the other 30-50% of the set's acceleration microvectors belong to the other one of the first or second vector group. In a non-limiting example, good marking quality and performance were achieved when 50% of the subseries' microvectors were in the first vector group, and 50% of the subseries microvectors were in the second group. The way with which said acceleration microvectors may be distributed between two consecutive vector groups may depend on the system moving the laser beam or on the laser system itself.

[0064] Preferably the vector speed of each of the microvectors can be calculated according to the following formula which correlates the “speed (i)” in a vector i, with the “speed (i−1)” of the vector i−1 which immediately precedes vector i:

[00009]$\begin{array}{cc}\mathrm{Speed}\left(i\right)\left[\frac{m}{s}\right]=\mathrm{Speed}\left(i-1\right)\left[\frac{m}{s}\right]+\frac{\mathrm{Speed}\left(i-1\right)\left[\frac{m}{s}\right]-\mathrm{Speed}\left(i\right)\left[\frac{m}{s}\right]}{\mathrm{Acceleration}\mathrm{Microvectors}},& \mathrm{equation}10.\end{array}$

[0065] In the optional case of having a constant microvector duration and having the number of acceleration microvectors determined according to equation 9, then equation 10 can be rewritten as follows:

[00010]$\begin{array}{cc}\mathrm{Speed}\left(i\right)\left[\frac{m}{s}\right]=\mathrm{Speed}\left(i-1\right)\left[\frac{m}{s}\right]+\frac{\mathrm{Speed}\left(i-1\right)\left[\frac{m}{s}\right]-\mathrm{Speed}\left(i\right)\left[\frac{m}{s}\right]}{\frac{2*\mathrm{Tracking}\mathrm{Error}\left[s\right]}{10\mathrm{\mu s}}},& \mathrm{equation}10.\end{array}$

[0066] In the example described by Tables 1 and 2 and FIG. 2, there is the following relationship:

Low Speed=0.5×Medium Speed=0.25×High Speed.

[0067] Moreover, in the example described by Tables 1 and 2 and FIG. 2, it is noted that D1/D2/D3=3/2/3 where D1 is the total distance (length) of the vectors (microvectors) in Vector group 1, D2 is the total distance (length) of the vectors (microvectors) in Vector group 2, and D3 is the total distance (length) of the vectors (microvectors) in Vector group 3.

[0068] Each of the vector groups may comprise a different number of vectors. The length of a vector (microvector) may be different between different vector groups. In the specific example described by Tables 1 and 2 and FIG. 2, there are 6 microvectors in vector 1, 8 microvectors in vector group 2, and 9 microvectors in vector group 3, and the vector speeds and vector powers set by the controller for each of the vectors (microvectors) in these three vector groups is shown in Table 3:

TABLE-US-00003 TABLE 3 Vector Marking Vector Vector Vector Group Intensity Speed Microvector Speed Power 1 1 High 1a 1.0x High 100% 1b 1.0x High 100% 1c 0.9x High  90% 1d 0.7x High  70% 1e 0.5x High  50% 1f 0.3x High  30% 2 3 Low 2a 1.0x Low 100% 2b 1.0x Low 100% 2c 1.0x Low 100% 2d 1.0x Low 100% 2e 1.0x Low 100% 2f 1.0x Low 100% 2g 1.0x Low 100% 2h 1.0x Low 100% 3 2 Medium 3a 0.5x Medium  50% 3b 0.7x Medium  70% 3c 0.8x Medium  80% 3d 0.9x Medium  90% 3e 1.0x Medium 100% 3f 1.0x Medium 100% 3g 1.0x Medium 100% 3h 1.0x Medium 100% 3i 1.0x Medium 100%

[0069] In Table 3 each of “High”, “Low” and “Medium” respectively corresponds to the High speed value, the Low speed and the Medium speed value. These values are usually, but not always, measured or expressed in mm/s. As is obvious, in Table 3 “0.5×High” means 0.5 times the High Speed value.

[0070] The vector power in Table 3 is the laser power that is set for each of the microvectors and is expressed as a percentage of a maximum laser power value. Hence, in the example of Table 3 a vector power that is 70% has a value that is 70% of the value of said maximum laser power.

[0071] From Table 3 it can be seen that in vector group 1 there are at least two vectors, e.g. vectors 1e and 1f, for which the controller of the system of FIG. 3 sets the vector speed and the vector laser power according to the marking intensity value of the corresponding vector group 1 such that said least two vectors (e.g. vectors 1e and 1f) within vector group 1 have with respect to each other different vector speeds and different vector laser powers. In the same example when the system marks vectors 1b to 1f on the surface of the object, the speed with which the laser beam travels on the surface of the object does not drop to zero while the laser beam hits said surface. Hence, the laser output's speed that is set according to the aforementioned at least two vectors (e.g. vectors 1e and 1f) remains different than zero when the laser output irradiates and travels along the two trajectory parts which correspond to said at least two vectors.

[0072] In Table 3 it can also be observed that vectors 1e and 1f from the particular vector group 1 and vector 2a from the subsequent vector group 2 form a subseries, wherein the particular and the subsequent vector groups 1 and 2 have different with respect to each other marking intensity values, and wherein the vectors 1e, 1f and 2a have with respect to each other different vector speeds, the vector speeds changing, more specifically decreasing, monotonically going from 1e to 2a, because the vector speed in 1e is 0.5×High, the vector speed of 1f is 0.3×High which is smaller than 0.5×High, and the vector speed of 2a is 1×Low=0.25High which is smaller than 0.3×High; this has happened because the controller of the system of FIG. 1 that is associated with the example of Table 3, is configured for setting the different vector speeds as described above.

[0073] FIG. 4. illustrates non-limiting examples of how the power of the laser output may be modified. In the example of FIG. 4 the laser output comprises pulses, and there are 8 consecutive vectors V1-V8 to mark, wherein the time T required for marking each of V1-V8 is constant, and wherein for each of V1-V3 the vector power is 25% of a full power value, for each of V4-V5 the vector power is 75% of the full power value, and for each of V6-V8 the vector power if 50% of the full power value. One contemplated way of modifying the laser power is as visually described in the direction (row) A in FIG. 4 where it is seen that there is a stream of laser pulses P with a constant period that is equal to T. So in A of FIG. 4 each pulse corresponds to a vector of the image to mark, and the duty cycle is modified by the laser system which produces the laser pulses according to the vector power which in turn, in this example, is set according to the corresponding color or grey level of the image. Therefore, in the case of A of FIG. 4 the laser output is pulsed, and for controlling the power of the laser output the laser system is configured for changing a duty cycle of the laser system. It is noted that in A of FIG. 4 the vector processing capacity is defined by the possible changes of duty cycle.

[0074] Direction/row B in FIG. 4 shows an alternative way to control the laser power. In the case of B in FIG. 4, the actual modulation to control the laser power is in a higher frequency compared to A, so that in B there are four laser pulses per vector. Compared to A, in B the modulation frequency has been multiplied by 4 but the changes of duty cycle happen with the same frequency as in A, thusly keeping in B the same vector processing capacity as in A. It is contemplated that the controller and/or the laser system in a preferred embodiment of the system according to the present invention, may be configured to control the number of laser pulses per vector, said number being 1 or higher. For example, the system may be configured to change between mode A and mode B. The number of pulses per vector may be controlled and changed by changing a modulation signal that may be applied on the laser system which produces the aforementioned pulsed optical output, wherein said modulation signal may modulate the power of the pulsed laser output. Said modulation signal may be controlled or changed by an appropriately configured controller.

[0075] FIG. 5 shows an example from which it can be understood how a vectorial image marking that is done according to the present invention may in principle be done faster than a traditional raster marking done line-by-line. FIG. 5 shows a graphic to be marked, the graphic consisting of a rectangle that has a portion R1 that is gray colored (gray color in FIG. 4 is indicated by the textured fill) and corresponds to a region where the laser output must affect, e.g. discolor, the surface of an object, and of a central square portion R2 that is not colored and corresponds to another region where the laser output must not affect the surface of the object. The traditional raster marking with the laser beam scanning the surface of the object line-by-line entails that the laser beam after scanning every line (the thick lines on FIG. 5) progressively moves towards the direction S as shown in A of FIG. 5. The disadvantage of marking as shown A in FIG. 5, is that the process is slow because the laser output unnecessarily is scanned across R2 where it is not supposed to cause any change on the object's surface. However, when using vectorial image marking for forming the same graphic on the object as shown in B of FIG. 5, the laser beam may first move following the general direction S1, then move following the general direction S2 and then finally move following the general direction S3, thereby scanning R1 without moving on R2. Hence, the vectorial marking may be much faster compared to the traditional raster marking.

[0076] Although the controller of the system according to the present invention is based in processing vectors, the image marking process may optionally start using a raster image that contains pixels which indicate the energy levels that need to be applied to the material. The image may be processed, e.g. with a computed that preferably is part of the system and communicates with the controller, using a known in the art algorithm to detect adjacent pixels of similar colour or greyscale values, and group them. Then, an also known in the art fastest path selection algorithm may be applied to find the most time-efficient route. An example of a known bitmap to vectorization algorithm is provided by the AutoTrace program that is available online for converting bitmap to vector graphics. (http://autotrace.sourceforge.net/).

[0077] A preferred embodiment of the method according to the second aspect of the invention is implemented on the basis of the described above function and operation of the preferred embodiment of the system which is according to the first aspect of the invention and can be used for implementing said method. While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. Those skilled in the art will understand that the embodiments disclosed here are non-limitative examples, and other embodiments are possible within the scope or the claims, for example but not limited to, different sequences of the method steps or different combinations of technical features.