Vacuum pulldown of print medium in printing system

1. A method for printing on a moving print medium in a printing system, including:

providing a first linehead defining one or more print zones, the first linehead adapted to jet a liquid on a first side of the print medium in the one or more print zones;

providing a plurality of transport rollers, wherein at least one transport roller is disposed opposite the first linehead, adjacent to a second side of the print medium, and is aligned with one of the print zones of the first linehead;

providing a vacuum assembly having a vacuum manifold disposed opposite the second side of the print medium, wherein the vacuum manifold of the vacuum assembly is aligned with the aligned transport roller, and wherein sealing rollers are disposed adjacent to the second side of the print medium and laterally adjacent to the vacuum manifold to prevent leakage of air;

moving the print medium through the printing system;

applying a vacuum force proximate to the second side of the print medium such that at least a portion of the moving print medium is deflected thereby increasing a wrap angle of the moving print medium around the aligned transport roller; and

jetting liquid from the first linehead onto the first side of the moving print medium to form a print.

2. The method according to claim 1 , further including connecting a vacuum source to the vacuum manifold.

3. The method according to claim 1 , further including providing an adjustment structure to adjust an effective width of the vacuum manifold, wherein the adjustment structure includes, a fixed cover having an array of apertures of varying dimensions and a sliding cover disposed adjacent to the fixed cover having an array of apertures with each aperture having a common fixed dimension, and further including using the adjustment structure to change the aperture size thereby changing the vacuum force operating on the print medium.

4. The method according to claim 1 , wherein the vacuum manifold defines a volume and further including adjusting the volume of the manifold to change the vacuum force operating on the print medium.

5. The method according to claim 1 , wherein the vacuum manifold partially surrounds the aligned transport roller and further including providing at least one opening in the vacuum manifold to cause the vacuum force to operate on the print medium.

6. The method according to claim 1 , wherein there are a plurality of transport rollers, each aligned with the one or more print zones of the first linehead, further including providing one or more vacuum manifolds connected to a vacuum source that cause a vacuum force to operate on the print medium and deflect the print medium causing an increase in the wrap angle of the print medium around each of the plurality of aligned transport rollers.

7. The method according to claim 6 , further including connecting the plurality of vacuum manifolds to a common vacuum plenum.

8. The method according to claim 7 , further including providing a plurality of vacuum adjustment mechanisms and using each vacuum adjustment mechanism to change the vacuum force provided by a corresponding one of the plurality of vacuum manifolds.

9. The method according to claim 1 , wherein the sealing rollers are rotatable when the print medium is moved through the print zone and further including providing an airflow gap between the sealing roller and the vacuum manifold to permit rotation of the sealing roller.

10. The method according to claim 1 , further including drying the liquid applied to the print medium.

11. The method according to claim 10 , further including:

providing a dryer and one or more dryer transport rollers disposed adjacent to the second side of the print medium and aligned opposite to the dryer;

providing a second vacuum manifold disposed opposite the second side of the print medium, wherein the second vacuum manifold is aligned with the dryer; and

using the second vacuum manifold to produce a second vacuum force that operates on the second side of the print medium to deflect the print medium causing an increase in the wrap angle of the print medium around the aligned dryer transport roller(s).

12. The method according to claim 1 , further including providing a second linehead disposed downstream of the first linehead such that a jetting direction of the second linehead is parallel to a jetting direction of the first linehead.

13. A method for printing on a moving print medium in a printing system, including:

providing a first linehead defining one or more print zones, the first linehead adapted to jet a liquid on a first side of the print medium in the one or more print zones;

providing a plurality of transport rollers, wherein at least one transport roller is disposed opposite the first linehead, adjacent to a second side of the print medium, and is aligned with one of the print zones of the first linehead, and wherein at least one transport roller is not aligned with any of the print zones of the first linehead;

providing a first vacuum assembly having a vacuum manifold disposed opposite the second side of the print medium, wherein the vacuum manifold of the vacuum assembly is aligned with the aligned transport roller; wherein sealing rollers are disposed adjacent to the second side of the print medium and laterally adjacent to the vacuum manifold to prevent leakage of air

providing a second vacuum assembly having a vacuum manifold disposed adjacent to the non-aligned transport roller such that the wrap angle of the moving print medium around the non-aligned transport roller prevents the formation of a wrinkle in the moving print medium; wherein sealing rollers are disposed adjacent to the second side of the print medium and laterally adjacent to the vacuum manifold to prevent leakage of air

moving the print medium through the printing system;

applying a vacuum force proximate to the second side of the print medium such that at least a portion of the moving print medium is deflected thereby increasing a wrap angle of the moving print medium around the aligned transport roller; and

jetting liquid from the first linehead onto the first side of the moving print medium to form a print.

14. The method according to claim 13 , wherein the vacuum manifold defines a volume and further including adjusting the volume of the manifold to change the vacuum force operating on the print medium.

15. The method according to claim 13 , further including:

providing a dryer and one or more dryer transport rollers disposed adjacent to the second side of the print medium and aligned opposite to the dryer;

providing a third vacuum manifold disposed opposite the second side of the print medium, wherein the third vacuum manifold is aligned with the dryer; and

using the third vacuum manifold to produce a third vacuum force that operates on the second side of the print medium to deflect the print medium causing an increase in the wrap angle of the print medium around the aligned dryer transport roller(s).

16. The method according to claim 1 , further including providing a second linehead disposed downstream of the first linehead such that a jetting direction of the second linehead is parallel to a jetting direction of the first linehead.

17. The method according to claim 13 , further including disposing the non-aligned transport roller between the aligned transport roller and a high wrap angle transport roller such that the non-aligned transport roller causes the print medium to curve in a direction opposite to the direction of curvature of the print medium at the high wrap angle transport roller.