The present invention relates to ink-jet printing systems, and more particularly, ink-jet printing systems which make use of ink containers that are pressurized to allow for high printing rates.
Ink-jet printers frequently make use of an ink-jet printhead mounted to a scanning carriage which is moved back and forth across a print media, such as paper. The printhead includes an ejector portion that faces the print media. The ejector portion is responsive to signals from a control system associated with the printing system for selectively ejecting ink droplets onto the print media. The carriage scans the ejector across the print media to print a swath. The media is then advanced to allow printing of another swath. In this way, ink droplets deposited by successive swaths form images and text on print media.
It is important that the images formed on print media have high print quality. Print quality is determined to a large extent by the proper operation of the printhead. A printhead typically includes an internal reservoir that is in fluid communication with the ejector. Critical to the proper operation of the ejector portion is the fluid pressure of the ink within the internal reservoir relative to an atmospheric pressure referred to as gauge pressure. A pressure regulation means is usually included with the printhead to control the gauge pressure within the internal reservoir.
Previously, some printers have made use of ink containers that are separately replaceable from the printhead. When the ink container is exhausted, the ink container is removed and replaced. The use of such separately replaceable ink containers allows for printing until the end of printhead life.
Some printers have also made use of "off-carriage" ink containers, wherein the ink containers are located off the scanning carriage. These off-carriage ink containers are typically coupled fluidically to the printhead internal reservoir by a tube. The use of off-carriage ink containers tends to reduce carriage weight, allowing for a more compact carriage that requires less power for movement, hence, smaller carriage motors to provide carriage motion. U.S. Pat. No. 5,650,811 describes such a configuration including an ink container coupled to a tube that is in turn coupled to a pressure regulator associated with the printhead. The pressure regulator assures that the ejector portion of the printhead receives ink at the proper pressure.
To allow the regulator to properly control pressure, the printing system utilizes an ink container that provides pressurized ink to the printhead. Delivery of ink to the printhead at a pressure that is equal to or greater than the operational pressure of the printhead is essential to ensure proper printhead operation. The regulator, in turn, regulates the fluid pressure of ink provided to the ejector portion to ensure proper operation of the printhead. The use of a regulator and a pressurized ink supply allows for the compensation for various design, layout, and environmental factors such as pressure drops, relative heights of the printhead and the ink supply, and atmospheric pressure changes.
Previously used ink-jet printing systems have used pressurized ink for various reasons. Examples of ink-jet components or systems utilizing pressurized ink are described in U.S. Pat. No. 4,558,326 to Kimura et al and U.S. Pat. No. 4,568,954 to Rosback.
One problem associated with pressurized ink containers is the effect that the internal pressure has on the container materials. Replaceable ink containers are preferably manufactured from low cost materials, such as plastic. A sustained internal pressure can cause these materials to permanently deform. This deformation, if severe enough, may render the ink container unusable. One example of how the ink container may become unusable is when the deformation prevents the ink container from fitting into an ink container receiving slot within the ink jet printing system.
There is an ever present need for ink containers for use in pressurized off carriage ink jet printing systems. These ink containers should be capable of use without deformation or leaking. In addition, these containers need to have a low manufacturing cost to minimize the cost of ink usage.