Ink reservoir

Details Ink reservoir Ink reservoir

1999-11-16

2001-08-07

Le, N. (Department: 2861)

Incremental printing of symbolic information

Ink jet

Fluid or fluid source handling means

C347S086000

Reexamination Certificate

active

06270208

ABSTRACT:

FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to ink supply for inkjet printers and, in particular, it concerns the subdivision of the volume of an ink supply reservoir into two or more inter-connected sub-volumes, to alleviate pressure fluctuations caused by acceleration of the reservoir.
It is known to employ an arrangement of one or more inkjet print heads in a scanning motion to achieve full print coverage across the length and width of a substrate. For certain applications, it is important to minimize the size and weight of the moving components and consequently, ink is supplied to the print head from a stationary ink reservoir. However, for other applications this is impractical, and the print head and reservoir move together on a print head assembly and hence execute the same motion. In order to achieve rapid printing, large velocities over short distances, and therefore large accelerations, are required of the print head and reservoir.
FIG. 1
shows a cross-sectional side view of a typical reservoir
600
and indicates a container which is composed of walls, including side walls
601
, a base
602
containing supply outlets
603
, and a lid
604
containing an atmosphere communication opening
605
, which together define a contained volume
608
. If the reservoir is accelerated in the primary direction of motion
609
, i.e. to the right, this results in a gradient of the ink level
607
where the magnitude of the gradient is proportional to the magnitude of the acceleration. Clearly, a similar, but opposite, situation would arise if the acceleration was in the opposite direction, i.e. to the left.
The liquid ink gradient induces a pressure gradient across the base of the reservoir, where the pressure above each ink supply outlet
603
, is proportional to the height of liquid ink above it. Furthermore, when reservoir
600
stops accelerating, gravity causes ink level
607
to tend towards the horizontal, thereby causing fluctuations in ink level
607
. Fluctuations of ink level
607
are highly undesirable for two main reasons. Firstly, effective operation of the print head (not shown) relies on a small and constant pressure differential between the print head and reservoir
600
. Small pressure fluctuations, on the order of millimeters of ink, between the print head and reservoir
600
can dramatically degrade the print quality. Secondly, if ink level
607
fluctuations become excessive, and the resulting pressure fluctuations exceed some threshold, this can result in total cessation of printing.
Another problem associated with acceleration is the inertial force acting on the liquid ink within the tubes, making up supply lines, connecting a print head and reservoir which are not aligned on the same plane normal to the direction of the acceleration. This scenario is depicted schematically in
FIG. 2
, which shows a top view of a print head assembly
509
. Print head assembly
509
is made up of an ink reservoir
500
, a print head
502
and a rigid plate
506
. Ink reservoir
500
and print head
502
are mounted rigidly on rigid plate
506
. Print head assembly
509
accelerates in a primary direction of motion
507
. A supply line
501
, from a supply outlet
503
of reservoir
500
, supplies ink to print head
502
via a print head supply inlet
505
. The distance between supply outlet
503
and supply inlet
505
, parallel to primary direction of motion
507
, is indicated
504
. When print head assembly
509
accelerates, an inertial force acts on the ink within supply line
501
which is proportional to length
504
. The inertial force in the supply line
501
causes a pressure fluctuation in print head
502
that is proportional to length
504
. Much like the example presented in
FIG. 1
, pressure fluctuations of this nature can be severe enough to dramatically reduce print quality or even bring about cessation of printing.
There is therefore a need for an ink reservoir for supplying ink to an inkjet print head which will overcome the aforementioned problem of pressure fluctuations. Specifically, there is a need to eliminate or significantly reduce reservoir ink level fluctuations which arise during print head assembly accelerations. Associated with this problem, there is a need to eliminate pressure fluctuations resulting from inertial forces acing on ink in supply lines during print head assembly accelerations.
SUMMARY OF THE INVENTION
The present invention is an ink reservoir, for inclusion in a moving inkjet print head assembly, and for connection, via an ink supply line, to at least one inkjet print head.
According to the teachings of the present invention there is provided, an ink reservoir, for inclusion in a moving inkjet print head assembly, and for connection, via an ink supply line, to supply ink to at least one inkjet print head. The ink reservoir comprises a container, formed from at least one wall and configured so as to define a contained volume for receiving ink, and at least one supply outlet being formed in the wall. Partitions are deployed so as to subdivide the contained volume into sub-volumes and pressure equilibration passages interconnect between the sub-volumes. The cross-sectional area of each pressure equilibration passage is less than about 10% of the area of each partition.
According to an alternative, or additional, aspect of the present invention there is provided an inkjet printer comprising a moving inkjet print head assembly, which includes an ink reservoir with supply outlets and print heads with supply inlets. The print head assembly is driven in a primary direction of motion such that planes substantially perpendicular to the primary direction of motion intersect corresponding reservoir supply outlets and print head supply inlets. The supply inlets may be displaced relative to one another in a direction having a non-zero component along the primary direction of motion.


REFERENCES:
patent: 5912689 (1999-06-01), Ostuka et al.
patent: 63-295270A (1988-12-01), None

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