Print head pulsing techniques for multicolor printers
View Patent ↗In one aspect of the invention there is disclosed a multicolor thermal imaging system wherein different heating elements on a thermal print head can print on different color-forming layers of a multicolor thermal imaging member in a single pass. The line-printing time is divided into segments, each of which is divided into a plurality of subintervals. All of the pulses within the segments have the same energy. In one embodiment, every pulse has the same amplitude and duration. Different colors are selected for printing during the different segments by varying the fraction of subintervals that contain pulses. This technique allows multiple colors to be printed using a thermal print head with a single strobe signal line. Pulsing patterns may be chosen to reduce the coincidence of pulses provided to multiple print head elements, thereby reducing the peak power requirements of the print head.
1. A device comprising:
first identification means for identifying a first plurality of pulses to be provided to a thermal print head in a first segment of a first line time, the first plurality of pulses having a first average power, wherein each of the first plurality of pulses has a common predetermined energy; and
second identification means for identifying a second plurality of pulses to be provided to the thermal print head in a second segment of the first line time, the second plurality of pulses having a second average power that is lower than the first average power, wherein each of the second plurality of pulses has the common predetermined energy; and
third identification means for identifying a third plurality of pulses to be provided to the thermal print head in a third segment of the first line time, the third plurality of pulses having a third average power that is lower than the first average power, wherein each of the third plurality of pulses has the common predetermined energy.
2. The device of claim 1 , wherein the first and second segments comprise a first portion and a second portion, the second portion including no pulses.
3. The device of claim 1 , wherein each of the first, second and third plurality of pulses has a common predetermined amplitude and a common predetermined duration.
4. The device of claim 3 , wherein the first line time comprises a plurality of subintervals, each of which is at least as long as the common predetermined pulse duration, and wherein the first identification means comprises:
means for identifying the number of pulses, P A , in the first plurality of pulses to be provided within the first segment of the first line time;
means for selecting a period N A ;
means for selecting a number A of consecutive subintervals to be allocated to the first segment of the first line time; and
means for allocating each of the first plurality of pulses to a single subinterval in the first segment of the first line time such that there are (N A −1) subintervals without pulses separating each subinterval that contains a pulse.
5. The device of claim 4 , wherein the second identification means comprises:
means for identifying the number of pulses, P B , in the second plurality of pulses to be provided within the second segment of the first line time;
means for selecting a period N B , where N B >N A ;
means for selecting a number B of consecutive subintervals to be allocated to the second segment of the first line time; and
means for allocating each of the second plurality of pulses to a single subinterval in the second segment of the first line time such that there are (N B −1) subintervals without pulses separating each subinterval that contains a pulse.
6. The device of claim 5 , wherein the third identification means comprises steps of:
means for identifying the number of pulses, P C , in the third plurality of pulses to be provided within the third segment of the first line time;
means for selecting a period N C , where N C >N B ;
means for selecting a number C of consecutive subintervals to be allocated to the third segment of the first line time; and
means for allocating each of the third plurality of pulses to a single subinterval in the third segment of the first line time such that there are (N C −1) subintervals without pulses separating each subinterval that contains a pulse.
7. The device of claim 6 , wherein the subintervals are of equal length.
8. The device of claim 7 , wherein N A =1, N B is an integer in the range 6-12, and N C is an integer in the range 15-25.
9. The device of claim 7 , wherein the values of A, B and C depend upon P A , P B , and P C , respectively.
10. The device of claim 7 , wherein the value of A is a preset default A′, and wherein the values of B and C depend upon P B and P C , respectively.
11. The device of claim 10 , wherein the value of B is N B *P B or a default value B′, whichever is less.
12. The device of claim 11 , wherein the number of subintervals in the first line time is t, and the value of C is N C times the value of INT((t−A−B)/N C ), where the function INT( )means “round down to the nearest integer”.
13. The device of claim 12 , wherein, for every line, out of a total of t subintervals in a line time, sequentially designated S 1 to S t , there is a particular subinterval S A , common to all heating elements, that can potentially be allocated a pulse by the means for allocating each of the first plurality of pulses; a particular subinterval S B , common to all heating elements, that can potentially be allocated a pulse by the means for allocating each of the second plurality of pulses; and a particular subinterval S C , common to all heating elements, that can potentially be allocated a pulse by the means for allocating each of the third plurality of pulses.
14. The device of claim 7 , wherein the smallest temporal separation between the start of any pulse in the first segment of the first line time and the start of any pulse in the second segment of the first line time is not greater than the duration of N B subintervals.
15. The device of claim 7 , wherein the smallest temporal separation between the start of any pulse in the first segment of the first line time and the start of any pulse in the third segment of the first line time varies between a maximum value of at least 0.5 milliseconds and zero in proportion to P A .
16. The device of claim 4 , wherein N A =1.
17. The device of claim 1 , further comprising:
first pulse provision means for providing the first plurality of pulses to the thermal print head in the first segment of the first line time;
second pulse provision means for providing the second plurality of pulses to the thermal print head in the second segment of the first line time; and
third pulse provision means for providing the third plurality of pulses to the thermal print head in the third segment of the first line time.
18. The device of claim 17 , wherein the first, second and third pulse provision means comprise a single strobe signal for producing the first plurality of pulses, the second plurality of pulses, and the third plurality of pulses.
19. The device of claim 17 , wherein the first pulse provision means comprises means for providing the first average power to the thermal print head in the first segment of the first line time to produce output having a first color on a thermal imaging member, and wherein the second pulse provision means comprises means for providing the second average power to the thermal print head in the second segment of the first line time to produce output having a second color that differs from the first color on the thermal imaging member, and wherein the third pulse provision means comprises means for providing the third average power to the thermal print head in the third segment of the first line time to produce output having a third color that differs from either the first color or the second color on the thermal imaging member.