Ink delivery apparatus for inkjet printhead

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.

FIGS. 1-3 are elevation views, partly in section, of an ink delivery apparatus according to a preferred embodiment of the invention, illustrating operation of the apparatus; and

FIG. 4 is an elevation view, partly in section, of an alternate embodiment of the ink delivery apparatus.

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.

FIG. 1 shows an ink delivery apparatus 10 for an DOD ink-jet printhead 12 . The ink delivery apparatus 10 includes a closed ink reservoir or ink accumulating chamber 14 fixed atop the printhead 12 . An ink 16 in the reservoir 14 is intended to drain first through a filter 18 and then through a bottom slot 20 , and into the printhead 12 . A slight-vacuum airspace 22 , i.e. one that is slightly below atmospheric pressure, exists above the ink level 24 in the reservoir. This is consistent with the known need to deliver the ink 16 to the printhead 12 at slight negative pressure known as a “back pressure”. Typically, as stated in prior U.S. Pat. No. 5,650,811 issued Jul. 22, 1997, the slight negative pressure in the printhead 12 may be approximately two to three inches of water below atmospheric pressure. The slight negative pressure is desired because it prevents the ink 16 from leaking, i.e. drooling, out of closely spaced ink discharge nozzles (not shown) in a nozzle plate 26 in the printhead 12 , 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.

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 FIGS. 1 and 2 .

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 FIG. 2 , when some ink 16 is delivered to the printhead, and by returning outwardly as shown in FIG. 1 , when some ink is replenished to the reservoir. Also, there is included a replenishment activator 36 that is connected to the pressure regulator membrane 32 outside the reservoir 14 to avoid being exposed to the ink 14 . The replenishment activator 36 initiates ink replenishment to the reservoir 14 when the pressure regulator membrane 32 deforms inwardly as shown in FIG. 2 and terminates ink replenishment when the pressure regulator membrane returns outwardly as shown in FIG. 1 .

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 FIG. 1 , to prevent ink replenishment to the reservoir, and to be stretched to uncap or open the ink conduit as shown in FIG. 2 , to allow ink replenishment to the reservoir. The replenishment activator 36 includes a rocker lever 44 that is pivotally mounted via a pivot pin 46 on the reservoir 14 and has a lever portion 48 connected to the pressure regulator membrane 32 and a lever portion 50 connected to the valve membrane 40 . The rocker lever 44 thus interconnects the pressure regulator membrane 32 and the valve membrane 40 to pivot clockwise about the pivot pin 46 as shown in FIG. 2 , to cause the valve membrane to uncap the ink conduit 38 when the pressure regulator membrane deforms inwardly, and to pivot counterclockwise about the pivot pin as shown in FIG. 1 , to recap the ink conduit when the pressure regulator membrane returns outwardly.

A spring 52 applies a counterclockwise pivoting force in FIG. 1 to the rocker lever 44 that causes the end portion 50 of the rocker lever which is connected to the valve membrane 40 to hold the valve membrane capping the ink conduit 30 . The pivoting force is light enough to be overcome when the pressure regulator membrane 32 deforms inwardly as shown in FIG. 2 .

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 FIG. 3 , the leaf spring 54 permits the portion 48 to be deformed away from the rocker arm 58 , without pivoting the rocker lever 44 about the pivot pin 46 , should the pressure regulator membrane 32 be further deformed outwardly (beyond its outward deformation in FIG. 1 ) when the valve membrane 40 is capping the ink conduit 38 . The pressure regulator membrane 32 might further deform outwardly in this instance due to a slight increase in the atmospheric pressure or a heating of the ink 16 in the reservoir 14 .

FIG. 4 shows an embodiment of the ink delivery apparatus 10 which is a modified version of the one shown in FIGS. 1-3 . In FIG. 4 , elements that are the same as in FIGS. 1-3 have the same reference numbers. One distinction however is that the spring 52 in FIG. 4 is a helical tension spring, whereas the spring 52 in FIGS. 1-3 is a helical compression spring.

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.

Parts List

10 . ink delivery apparatus

12 . inkjet printhead

14 . ink reservoir

16 . ink

18 . filter

20 . bottom slot

22 . airspace

24 . ink level

26 . nozzle plate

28 . pressure regulator and ink replenishment mechanism

30 . ink supply source

32 . pressure regulator membrane

34 . opening

36 . replenishment activator

38 . ink conduit

40 . valve membrane

42 . opening

44 . rocker lever

46 . pivot pin

48 . lever portion

50 . lever portion

52 . spring

54 . leaf spring

56 . spring end

58 . rocker arm