Pulse waveforms for ink jet printing

1. A digital printing system, comprising:

a print head, configured to jet droplets of ink; and

a processor, which is configured to:

translate a required shade of a color, to be printed at a given location on a substrate by the print head, into a sequence of one or more pulses,

wherein for at least one shade, the sequence of one or more pulses comprises:

up to a predefined maximum number of driving pulses that cause the print head to jet respective droplets; and

a tickling pulse, which has a smaller amplitude than the driving pulses and is such that when the tickling pulse is applied just after a driving pulse, it causes the print head to jet a droplet, while if the tickling pulse is applied not just after a driving pulse, it does not cause the print head to jet a droplet; and

apply the sequence of pulses to the print head.

2. The system according to claim 1 , wherein a time duration of at least one of the driving pulses in the sequence of one or more pulses matches a resonance frequency of a pressure wave in the ink inside a jetting channel of the print head.

3. The system according to claim 2 , wherein the time duration of the at least one of the driving pulses is set depending on a type of the ink.

4. The system according to claim 1 , wherein the processor is configured to set an amplitude of the driving pulses to achieve a maximal speed of the jetted droplets.

5. The system according to claim 1 , wherein the tickling pulse is at an end of the sequence for the at least one shade.

6. The system according to claim 1 , wherein the driving pulses and the tickling pulse have a same duration.

7. The system according to claim 1 , wherein the tickling pulse has an amplitude which when applied just after a driving pulse, causes the print head to jet a droplet smaller than the droplets jetted in response to the driving pulses.

8. The system according to claim 1 , wherein the processor is configured to convert a plurality of different required shades into respective pulse sequences, the pulse sequences all having a same duration defining a given number of sections in which pulses may be applied and each shade has a corresponding pulse sequence with a different combination of the sections in which pulses are applied.

9. The system according to claim 8 , wherein the given number of sections includes driving pulse sections which include driving pulses in respective pulse sequences of corresponding to one or more of the shades, and a tickling pulse section, which includes a tickling pulse in respective pulse sequences corresponding to a plurality of the shades.

10. The system according to claim 9 , wherein the tickling pulse section includes a tickling pulse only in the respective pulse sequences of a brightest shade and a darkest shade.

11. A digital printing method, comprising:

defining a required shade of a color, to be printed at a given location on a substrate by a print head that jets droplets of ink;

translating the required shade of the color into a sequence of one or more pulses, and

applying the sequence of pulses to the print head,

wherein the sequence of pulses for at least one shade comprises:

up to a predefined maximum number of driving pulses that cause the print head to jet respective droplets; and

a tickling pulse, which has a smaller amplitude than the driving pulses and is such that when it is applied just after a driving pulse it causes the print head to jet a droplet, while if the tickling pulse is applied not just after a driving pulse, it does not cause the print head to jet a droplet.

12. The method according to claim 11 , wherein translating the required shade into the sequence of pulses comprises setting, for at least one of the pulses in the sequence of pulses, a time duration that matches a resonance frequency of a pressure wave in the ink inside a jetting channel of the print head.

13. The method according to claim 11 , wherein the tickling pulse has an amplitude which when applied just after a driving pulse, causes the print head to jet a droplet smaller than the droplets jetted in response to the driving pulses.

14. The method according to claim 11 , and comprising setting an amplitude of the driving pulses to achieve a maximal speed of the jetted droplets.

15. The method according to claim 11 , wherein applying the sequence of pulses comprises applying the tickling pulse at an end of the sequence of pulses.