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A printing control method of a multi-nozzle binary continuous ink jet printer wherein drops of a first category and drops of a second category are formed by jet breaking. The flowpaths followed by the drops of the first and second categories are differentiated. For printing a black pixel followed by

A printing control method of a multi-nozzle binary continuous ink jet printer wherein drops of a first category and drops of a second category are formed by jet breaking. The flowpaths followed by the drops of the first and second categories are differentiated. For printing a black pixel followed by a white pixel, a drop of the first category and a drop of the second category are formed. The cumulative formation time drops of the first and second categories is equal to or higher than the running time of one pixel.

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1. A printing control method for a multi-nozzle binary continuous ink-jet printer or print head of such a printer for printing a pattern on a printing medium moving with respect to the head, the method comprising: providing a head comprising a multi-nozzle drop generator includinga body includingone

1. A printing control method for a multi-nozzle binary continuous ink-jet printer or print head of such a printer for printing a pattern on a printing medium moving with respect to the head, the method comprising: providing a head comprising a multi-nozzle drop generator includinga body includingone or more pressurised chambers each able to receive ink under pressure,ejecting nozzles in hydraulic communication with a pressurised chamber and each able to eject an ink jet having a rate Vj along a longitudinal axis (A) thereof, the ejecting nozzles being aligned along an aligning axis and arranged on a same plane,a plurality of actuators configured to cause, on pulse order, breaking of a jet ejected from a nozzle to form a succession of drops,the medium having with respect to the head, a rate Vs, the distance between consecutive pixels in the direction of movement of the medium being Dii;forming drops of a first category and drops of a second category by jet breaking, the drops of the first category each having a first volume, all the first volumes being substantially equal, the drops of the second category having second volumes not necessarily equal but all the drops of the second category having a volume which is not equal to the volume of a drop of the first category;differentiating the flowpaths followed by the drops of the first and second categories by applying to at least one of the drop categories a deflection force able to differentiate the flowpaths of drops of the first category and drops of the second category, the flowpath of drops of the first category intersecting the printing medium and the flowpath of drops of the second category intersecting a gutter for recovering such drops;creating a piece of information relating to moments where consecutive pixels to be printed run in a position where they are likely to be printed; andfor printing each black pixel of the pattern which is followed by a white pixel of the pattern, forming one single drop of the first category and one single drop of the second category, wherein a time for forming one of said drops is less than a running time of one pixel and a cumulative time for forming said single drops of the first and second categories is equal to or higher than a running time of one pixel. 2. The printing method according to claim 1, wherein, for printing each black pixel of the pattern, said one single drop of the first category and said one single drop of the second category are formed, the cumulative time for forming the drop of the first category and the drop of the second category being equal to a running time Dp of the medium by the distance Dii. 3. The printing method according to claim 1, wherein for forming each white pixel of the pattern, one single drop of the second category is formed, the formation time thereof being at least equal to a running time Dp of the medium by a distance Dii. 4. The printing method according to claim 1, further comprising: wherein, before printing a current pixel of the pattern, determining whether a following pixel is a white or black pixel, and if the current pixel is black and the following pixel is white, forming a single drop of the first category for printing the current pixel, and then forming a single drop of the second category, the formation time of said single drops of the first and second categories being at least equal to twice the running time of one pixel. 5. The printing method according to claim 4, wherein the rate Vs is a running rate selected so that the running time Dp of one pixel is equal to pda, p standing for an integer and da standing for the formation time of one drop of the first category. 6. The printing method according to claim 1, wherein for printing each succession of n consecutive black pixels of the pattern, n standing for an integer equal to or higher than 2, drops of the first category are formed for a time equal to the running time of (n−1) black pixels plus a time between 1 and 2 times the formation time of one single drop of the first category. 7. The printing method according to claim 1, further comprising: for printing each black pixel of the pattern, forming one single drop of the first category and one single drop of the second category, the cumulative time for forming the single drop of the first category and the single drop of the second category being equal to a running time Dp of the medium by the distance Dii, as long as the relative rate of the medium and the printing head, rate Vs, is lower than a value Vs0, ordetermining, before printing a current pixel of the pattern, whether a following pixel is a white or black pixel, and if the current pixel is black and the following pixel is white, forming a single drop of the first category for printing the current pixel, and then forming a single drop of the second category, the formation time of said single drops of the first and second categories being at least equal to twice the running time of one pixel, as long as the relative rate of the medium and the printing head Vs is higher than a value Vs0. 8. The printing method according to claim 7, wherein the value Vs0 is the rate for which Dp=Dii/Vs0 is equal to (1+Rm)da, in which formula Dp stands for the running time by the distance Dii for the rate Vs0, da stands for the formation time of one drop of the first category, Rm stands for the minimum value which should be assumed by the ratio R of the volume of a drop of the second category to the volume of a drop of the first category so that the flowpaths of drops of the first and second categories are markedly differentiated in view of a separation mode of flowpaths. 9. The printing method according to claim 1, wherein, when the running rate of the medium is higher than a threshold, positional information of the medium from medium position measuring means is substituted by information calculated from information received by these means. 10. The printing method according to claim 9, wherein the substituted information is recalculated after each printing of an entire pattern. 11. The printing method according to claim 1, wherein, when the rate Vs is a running rate such that a running time Dp of one pixel is determined by taking a value between two integers times k and k+1, where k is a number of drops, of a formation time, da, of one drop of the first category, said formation time da is changed to a different formation time, da′, such that the running time Dp is equal to k*da′ or (k+1)*da′. 12. The printing method according to claim 11, wherein, when the running rate Vs of the medium ranges between a first rate Vsk and a second rate Vsk+1 for which the running time Dp is equal to kda and (k+1)da, respectively, and is equal to (k+z)da within the range of these two values, z being a number ranging from 0 to 1, the formation time of drops is increased as long as z is lower than a value z1 and forming k drops having a formation time da′=da(k+z1)/(k+1) per pixel is continued, and when z is equal to or higher than the value z1, k+1 drops having a formation time da″=da(k+z1)/(k+1) per pixel are formed. 13. The printing method according to claim 1, wherein the formation time of drops is determined either by a time of a deviation bet en two consecutive pulses received by the actuators, or by energy level of one pulse received by the actuators. 14. The printing method according to claim 1, wherein differentiating the flowpaths followed by single drops of the first and second categories respectively is achieved either by applying an electrostatic force to drops of the second category, or by applying to drops of the first and second categories a wind (W) with a direction transverse to the flowpath of the drops. 15. A printer or printing head comprising: ahead comprising a multi-nozzle drop generator including;a body including; one or more pressurised chambers each able to receive ink under pressure;ejecting nozzles in hydraulic communication with a pressurised chamber and each able to eject an ink jet having a rate Vj along a longitudinal axis (A) thereof, the ejecting nozzles being aligned along an aligning axis and arranged on a same plane; anda plurality of actuators configured to cause, on pulse order, breaking of a jet ejected from a nozzle to form a succession of drops,wherein the head is configured to form drops of a first category and drops of a second category by jet breaking, the drops of the first category each having a first volume, all the first volumes being substantially equal, the drops of the second category having second volumes not necessarily equal but all the drops of the second category having a volume which is not equal to the volume of a drop of the first category;differentiate flowpaths followed by the drops of the first and second categories by applying to at least one of the drop categories a deflection force able to differentiate the flowpaths of drops of the first category and drops of the second category, the flowpath of drops of the first category intersecting a printing medium and the flowpath of drops of the second category intersecting a gutter for recovering such drops;create information relating to moments where consecutive pixels to be printed run in a position where they are likely to be printed; andfor printing each black pixel of the pattern which is followed by a white pixel of the pattern, forming one single drop of the first category and one single drop of the second category, wherein a time for forming one of said drops is less than a running time of one pixel, and a cumulative time for forming said single drops of the first and second categories is equal to or higher than a running time of one pixel. 16. The printer or printing head according to claim 15, wherein, for printing each black pixel of the pattern, the head is further configured to form one single drop of the first category and one single drop of the second category, the cumulative time for forming the single drop of the first category and the single drop of the second category being equal to a running time Dp of the medium by a distance Dii representing a distance between consecutive pixels in a direction of movement of the head. 17. The printer or printing head according to claim 15, wherein for forming each white pixel of the pattern, the head is further configured to form one single drop of the second category, the formation time thereof being at least equal to a running time Dp of the medium by a distance Dii representing a distance between consecutive pixels in a direction of movement of the head. 18. The printer or printing head according to claim 15, wherein the head is further configured to, before printing a current pixel of the pattern, determine whether a following pixel is a white or black pixel, and if the current pixel is black and the following pixel is white, to form a single drop of the first category for printing the current pixel, and then form a single drop of the second category, a formation time of said single drops of the first and second categories being at least equal to twice a running time of one pixel. 19. The printer or printing head according to claim 15, wherein for printing each succession of n consecutive black pixels of the pattern, n representing an integer equal to or higher than 2, the head is further configured to form drops of the first category being formed for a time equal to the running time of (n−1) black pixels plus a time between 1 and 2 times a formation time of one drop of the first category. 20. The printer or printing head according to claim 19, wherein a rate Vs is running rate selected so that a running time Dp of one pixel is equal to pda, p representing an integer and da representing the formation time of one drop of the first category. 21. The printer or printing head according to claim 15, wherein, for printing each black pixel of the pattern, the head is further configured to form one single drop of the first category and one single drop of the second category, a cumulative time for forming the single drop of the first category and the single drop of the second category being equal to a running time Dp of the medium by a distance Dii representing a distance between consecutive pixels in a direction of movement of the head, as long as a relative rate of the medium and the head, rate Vs, is lower than a value Vs0, orwherein, before printing a current pixel of the pattern, the head is further configured to determine whether a following pixel is a white or black pixel, and if the current pixel is black and the following pixel is white, to form a single drop of the first category for printing the current pixel, and then to form a single drop of the second category, a formation time of said simile drops of the first and second categories being at least equal to twice a running time of one pixel, as long as a relative rat of the medium and the head Vs is higher than a value Vs0. 22. The printer or printing head according to claim 21, wherein the value Vs0 is a rate for which Dp=Dii/Vs0 is equal to (1+Rm)da, in which formula Dp represents a running time by a distance Dii for the rate Vs0, Dii represents a distance between consecutive pixels in a direction of movement of the head, da represents a formation time of one drop of the first category, and Rm represents a minimum value which should be assumed by the ratio R of the volume of a drop of the second category to the volume of a drop of the first category so that the flowpaths of drops of the first and second categories are markedly differentiated in view of a separation mode of flowpaths. 23. The printer or printing head according to claim 15, wherein, when the running rate of the medium is higher than a threshold, positional information of the medium from medium position measuring means is substituted by information calculated from information received by said medium positioning measuring means. 24. The printer or printing head according to claim 23, wherein the substituted information is recalculated after each printing of entire pattern. 25. The printer or printing head according to claim 15, wherein, when the rate Vs is a running rate such that a running time Dp of one pixel is determined by taking a value between two integers times k and k+1, where k is a number of drops, of a formation time, da, of one drop of the first category, said formation time da is changed to a different formation time, da′, such that the running time Dp is equal to k*da′ or (k+1)*da′. 26. The printer or printing head according to claim 25, wherein, when the running rate Vs of the medium ranges between a first rate Vsk and a second rate Vsk+1 for which the running time Dp is equal to kda and (k+1)da, respectively, and is equal to (k+z)da within the range of these two values, z being a number ranging from 0 to 1, the formation time of drops is increased as long as z is lower than a value z1 and forming k drops having a formation time da′=da(k+z1)/(k+1) per pixel is continued, and when z is equal to or higher than the value z1, k+1 drops having a formation time da″=da(k+z1)/(k+1) per pixel are formed. 27. The printer or printing head according to claim 15, wherein the formation time of drops is determined either by a time of a deviation between two consecutive pulses received by the actuators, or by an energy level of one pulse received by the actuators. 28. The printer or printing head according to claim 15, wherein differentiating the flowpaths followed by drops of the first and second categories respectively is achieved either by applying an electrostatic force to drops of the second category, or by applying to drops of the first and second categories a wind (W) with a direction transverse to the flowpath of the drops.