Active biased electrodes for reducing electrostatic fields underneath print heads in an electrostatic media transport
View Patent ↗Embodiments described herein are directed to a system for reducing electrostatic fields underneath print heads in a direct marking printing system. The system includes: one or more print heads for depositing ink onto a media substrate; a media transport for moving the media substrate along a media path past the one or more print heads; a conductive platen contacting the media transport belt; an electrostatic field reducer that includes an alternating current charge device positioned upstream of the one or more print heads; and one or apertures with electrically isolated biased electrodes separated by an opening that is in registration with the ink deposition areas of the one or more print heads. The media transport includes a media transport belt and, when the media is on the transport belt it has an electrostatic field, which can cause printing defects. The electrostatic field reducer and electrodes reduce the electrostatic field on the surface of the media and thereby reduce printing defects.
1. A system for reducing electrostatic fields underneath print heads, the system comprising:
one or more print heads for depositing ink onto a surface of a media substrate in one or more ink deposition areas;
a media transport for moving the media substrate along a media path in a process direction past the one or more print heads, wherein the media transport comprises a media transport belt, and wherein the media has an electrostatic field;
a conductive platen contacting the media transport belt, wherein the media transport belt is disposed between the conductive platen and the one or more print heads;
one or more apertures in the conductive platen, wherein each aperture extends lengthwise in a trans-process direction between a first end and a second end and widthwise in the process direction between a first side and a second side;
two electrically isolated biased electrodes positioned at the first and second sides of each of the one or more apertures to define one or more openings therebetween, wherein the one or more openings are in registration with the locations of the one or more ink deposition areas of the one or more print heads; and
one or more voltage sources for providing a voltage to the two electrically biased electrodes in each of the one or more apertures,
wherein the voltage is provided to the electrically biased electrodes to reduce the electrostatic field on the surface of the media receiving the ink.
2. The system for reducing electrostatic fields underneath print heads according to claim 1 , wherein the one or more voltage sources independently supply voltages to the two electrically biased electrodes.
3. The system for reducing electrostatic fields underneath print heads according to claim 1 further comprising a field probe or a non-contacting electrostatic voltmeter for measuring an electrical field at a location upstream in the process direction of the one or more print heads.
4. The system for reducing electrostatic fields underneath print heads according to claim 1 further comprising a controller for adjusting the voltage provided to the two electrically isolated biased electrodes.
5. The system for reducing electrostatic fields underneath print heads according to claim 1 , wherein the one or more openings has a dimension in the process direction and in a trans-process direction that extends at least 3 mm beyond the ink deposition areas that are in registration with the one or more openings.
6. The system for reducing electrostatic fields underneath print heads according to claim 1 , wherein the one or more openings has a dimension in the process direction and in a trans-process direction that extends at least 5 mm beyond the ink deposition areas that are in registration with the one or more openings.
7. The system for reducing electrostatic fields underneath print heads according to claim 1 , wherein the media transport belt is formed from insulating or semi-conductive materials.
8. The system for reducing electrostatic fields underneath print heads according to claim 7 , wherein the semi-conductive materials in the media transport belt are formed in layers and have a sheet resistivity greater than 10 8 ohms/sq.
9. The system for reducing electrostatic fields underneath print heads according to claim 1 , wherein the voltage provided by the voltage source is from 1 to 3,000 volts.
10. The system for reducing electrostatic fields underneath print heads according to claim 1 , wherein a plurality of apertures is arranged in a staggered full width array.
11. The system for reducing electrostatic fields underneath print heads according to claim 1 , wherein the system further comprises one or more rollers for electrostatically tacking the media substrate onto the media transport belt.
12. The system for reducing electrostatic fields underneath print heads according to claim 1 further comprising an electrostatic field reducer comprising a voltage sensitive charge device positioned upstream of the one or more print heads in the process direction.
13. The system for reducing electrostatic fields underneath print heads according to claim 12 , wherein the voltage sensitive charge device is an AC corona device that drives the potential of the media to zero voltage.
14. The system for reducing electrostatic fields underneath print heads according to claim 12 , wherein the two electrically isolated biased electrodes are electrically insulated from the platen.
15. The system for reducing electrostatic fields underneath print heads according to claim 12 , wherein the voltage sensitive charge device discharges onto the surface of the media substrate at a location above a grounded region of the conductive platen or at least 10 mm distant from a grounded region of the conductive platen.
16. The system for reducing electrostatic fields underneath print heads according to claim 1 , wherein the electrostatic field reducer reduces the electrostatic field to less than 5 V/micron on the surface of the media receiving the ink.
17. The system for reducing electrostatic fields underneath print heads according to claim 1 , wherein the electrostatic field reducer reduces the electrostatic field on the surface of the media receiving the ink to less than 1 V/micron.