The invention generally relates to inkjet printing, and more particularly to an ink delivery apparatus for an inkjet printhead.
Inkjet printers can be divided into two major categories, commonly referred to as continuous inkjet and drop-on-demand (DOD) ink-jet.
In DOD inkjet printers, the ink delivery apparatus for an ink-jet printhead delivers the ink to the printhead at a slight vacuum or negative pressure known as a “back pressure”. The slight negative pressure in the printhead is desired because it prevents the ink from leaking, i.e. drooling, out of closely spaced ink discharge nozzles in the printhead, by tending to draw the ink at the nozzles back into the printhead. Moreover, it forms a slightly concave ink meniscus at each nozzle which helps to keep the nozzle clean. Typically, as stated in prior art U.S. Pat. No. 5,650,811 issued Jul. 22, 1997, the slight negative pressure in the printhead may be approximately two to three inches of water below atmospheric pressure. The patent also states that the slight negative pressure can be created by positioning an ink reservoir for the printhead below the printhead. Alternatively, the slight negative pressure can be created by using a nonlinear spring to pull a membrane bladder outward at an opening in an ink reservoir above the printhead. This latter approach is described in detail in U.S. Pat. No. 4,509,062 issued Apr. 2, 1985.
Today, most DOD inkjet printheads have an “onboard” ink reservoir. In other words, the ink reservoir is fixed atop the printhead and moves with it during the printing operation. Often, as disclosed in prior art U.S. Pat. No. 5,975,689 issued Nov. 2, 1999 and U.S. Pat. No. 5,872,584 issued Feb. 16, 1999, the negative pressure regulator is coupled with an ink replenishment mechanism, both of which are located inside the ink reservoir. However, a problem that can occur with locating the negative pressure regulator and ink replenishment mechanism inside the reservoir is that it is subject to corrosion and chemical attack by the ink inside the reservoir. Also, the mechanism may contaminate the ink.
An ink delivery apparatus for an inkjet printhead, comprising an ink reservoir for delivering some ink at a slight negative pressure to a printhead, and a pressure regulator and ink replenishment mechanism that maintains substantially constant negative pressure in the reservoir when some ink in the reservoir is delivered to the printhead and in response to the ink delivery replenishes someink to the reservoir from an ink supply source, is characterized in that:
the pressure regulator and ink replenishment mechanism includes a pressure regulator member that air-tightly covers an opening in the reservoir and is compliant to maintain substantially constant negative pressure in the reservoir, and a replenishment activator connected to the pressure regulator member outside the reservoir to avoid being exposed to the ink and which initiates ink replenishment to the reservoir when some ink in the reservoir is delivered to the printhead.
The invention is depicted as embodied in a drop-on-demand (DOD) inkjet printer. Because the features of such a printer are generally known, the description which follows is directed in particular only to those elements forming part of or cooperating with the disclosed embodiment of the invention. It is to be understood, however, that other elements not disclosed may take various forms known to a person of ordinary skill in the art.
A pressure regulator and ink replenishment mechanism 28 maintains substantially constant negative pressure in the reservoir 14 when some ink 16 in the reservoir is delivered to the printhead 12, and in response to the ink delivery replenishes some ink to the reservoir from a pressurized ink supply source 30. This an be seen by comparing
The pressure regulator and ink replenishment mechanism 28 includes a pressure regulator membrane or diaphragm 32 that air-tightly covers an opening 34 in the reservoir 14. The pressure regulator membrane 32 is compliant in order to maintain substantially constant negative pressure in the reservoir 14 by deforming inwardly as shown in
An ink conduit 38, such as a tube, longitudinally extends from the pressurized ink source 30 into the reservoir 14. The ink conduit 38 empties into the reservoir 14 as shown in FIG. 2.
The replenishment activator 36 includes a valve membrane or diaphragm 40 that air-tightly covers an opening 42 in the reservoir 14. The valve membrane 40 is compliant to normally cap or close the ink conduit 38 substantially at the opening 42 as shown in
A spring 52 applies a counterclockwise pivoting force in
The portion 48 of the rocker lever 44 that is connected to the pressure regulator membrane 32 is actually the free end of a cantilevered leaf spring 54 whose other end 56 is anchored to a rigid rocker arm 58. The rocker arm 58 has a free end that is the portion 50 of the rocker lever which is connected to the valve diaphragm 40. As shown in
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
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Number | Date | Country |
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1 120 259 | Aug 2001 | EP |
Number | Date | Country | |
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20040165039 A1 | Aug 2004 | US |