Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
1997-02-13
2001-01-09
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
Reexamination Certificate
active
06172694
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to ink jet printing, and, more specifically, to ink jet printing systems used to imprint packages or cartons with various indicia as the packages are conveyed past an ink jet printhead at a printing station positioned along a conveyor path. Such inkjet printing systems are oftentimes used to imprint shipping information, bar codes, lot numbers and other production or shipping information on overcartons or secondary packaging in a production packaging line or the like. The printhead of such inkjet printing systems is typically supplied with ink from an ink supply remote from the printhead by means of appropriate ink tubes or lines.
Because the printheads are located in close proximity to the cartons (or other objects to be imprinted) as they are conveyed past the printhead if a carton is not properly positioned on the conveyor line, the carton may come into contact with the printhead as the carton is conveyed therepast. In some applications, the cartons are conveyed past the printhead with considerable speed (up to 150 feet/minute or more) and the cartons are heavy. Upon the printhead being hit by one of these heavy cartons being conveyed at such speeds, a considerable impact or shock load is imparted to the printhead. It is known that such impact loads can cause the printhead to de-prime.
It is believed that upon the above-described shock load being imparted to the printhead, a back pressure or shock wave is generated within the ink supply line which travels at extremely high speed through the ink supply line toward the ink reservoir. This shock wave can so reduce the pressure within the ink supply line as to de-prime the printhead. More specifically, and especially with capillary ink feed systems, it is believed that the shock wave may generate back pressures in the ink supply system sufficient to break the meniscus of the ink in the ink orifices of the printhead thus de-priming the printhead. Such de-priming of the printhead is a serious problem.
In the event the printhead de-primes, the printhead will not print until it again is primed with ink. If cartons conveyed past the printhead in a production packaging line are not imprinted, the cartons must be removed from the production line and must either be manually marked or, after the printhead is re-primed, must be positioned on the conveyor line so as to be again conveyed past the printhead for being properly imprinted by the printhead. This, of course, can cause major problems on a production line using such ink jet printing systems.
In addition, it is a time consuming process to re-prime a printhead during which time the packaging line on which the printing system is installed must be shut down. Of course, it is highly undesirable and costly to shut down a production packaging line. In addition, with certain ink jet printing systems, special inks are required to prime the printheads. These special priming inks are expensive and are time consuming to use.
It has long been a goal for such ink jet print systems, and particularly for capillary ink feed systems, to lessen the tendency of the printhead to de-prime. One way of reducing the tendency of the printhead to de-prime has been to incorporate a check valve in the ink supply line between the ink reservoir and the printhead. Upon a back pressure or shock wave being generated in the printhead and traveling back through the ink supply line, and upon this back pressure or shock wave encountering the check valve, the check valve will close thus preventing the shock wave from traveling to the ink supply. However, it has been found that the incorporation of prior art check valves (as hereinafter described in detail), in the ink supply circuit has not abated the tendency of the printhead to de-prime. It is believed that movement of the check valve member from its open to its closed position can sometimes generate a region of low pressure within the ink supply system which can cause a pressure differential of sufficient magnitude to result in de-priming of the printhead.
Still further, the incorporation of a check valve in the ink supply system has other draw backs. First, if the check valve is normally closed, upon initiating flow of ink to the printhead (which is usually in pulses rather than in a steady state flow), the normally closed check valve will require a higher pressure to initially open the check valve (referred to as a cracking pressure). Further, such check valves are susceptible to contamination from particles in the ink such that an accumulation of such contamination particles may adversely affect the operation of such check valve. Still further, the incorporation of such a check valve in the ink supply lines causes a flow restriction that may adversely affect the flow of ink to the printhead and may increase the response time of the ink supply system to the printhead.
As noted, prior art printheads have used check valves in the past. As shown in
FIG. 10
of the drawings, a first embodiment of such a prior art check valve is shown which has been used with a capillary ink supply system for an ink jet printhead. This prior art check valve, as indicated in its entirety at
101
, has a valve body
103
having an inlet
105
and an outlet
107
with a check valve chamber
109
therewithin. A check valve member, as indicted at
111
, is provided in chamber
109
which is movable from a closed position in which the downstream face of the check valve member is in sealing engagement with the downstream face of the chamber
109
surrounding inlet
105
so as to block the backflow of ink from chamber
109
into inlet
105
. Upon the check valve member
111
being subjected to normal flow via the inlet
105
from the ink supply to the printhead, the flow will cause the check valve member
111
to shift from its above-described closed position to an open position within chamber
109
in which ink may flow around the periphery of the check valve member
111
and to be discharged from the outlet
107
for flowing to the printhead. In such prior art check valves, the check valve member
111
was typically made of a flexible, resilient elastomer, such as a suitable silicone rubber material or the like, and the check valve member has a diameter somewhat less than the inner diameter of chamber
109
such that the check valve member is free to move within the chamber between its open and its closed positions. As shown, with the check valve member
111
in its open position, the ink is free to enter the chamber
109
on the downstream face of check valve member
111
and to flow around the periphery of the check valve member and to flow to outlet
107
.
It will be appreciated that the average flow rate of ink through the above-noted check valves to the printhead is very low (e.g., about 0.5 ml./min.). Moreover, the size of such check valves is small. For example, the diameter of the check valve member
111
, as shown in
FIG. 8
may only be about 0.110 inches. Referring again to the check valve shown in
FIG. 7
, upon a shock wave (back pressure pulse) traveling from the printhead to the check valve, the shock wave will travel through the outlet
107
and will enter chamber
109
. There, the back pressure or shock wave will act against the entire upstream face of valve member
111
thus causing the member to move axially within chamber
109
to its closed position. However, upon the valve member moving within the chamber from its open to its closed position, the volume of the chamber on the upstream side of the valve member expands greatly and thus generates a low pressure void within the valve chamber. This in turn lowers the pressure within the ink supply line upstream from the check valve and within the printhead. This low pressure may be sufficient to overcome the meniscus force of the ink within the ink orifices of the printhead and thus may result in de-priming of one or more orifices of the printhead. Thus, even with the presence of such check valve in the ink supply system, the check valve did not eliminate the de-priming pro
Droege Curtis R.
Kuester Kevin W.
Sherman Donald E.
Le N.
Marconi Data Systems Inc.
Polster Lieder Woodruff & Lucchesi
Vo Anh T. N.
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