Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
1999-04-30
2001-07-31
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
Reexamination Certificate
active
06267473
ABSTRACT:
FIELD OF INVENTION
The present invention generally relates to ink-jet printers and, more particularly, to the apparatus and methods for transporting the ink used by such printers from an ink reservoir to an inkjet print head.
BACKGROUND OF THE INVENTION
Check valves or their equivalents have been probably known since the development of the first fluid displacement pumps. Moreover, ink-jet printers have been commercially available since at least the late 1980's, and their general construction is also well known, being the subject of numerous patents world-wide.
Nevertheless, developing a simple, low cost, dependable check valve for the ink pumps used in these printers has proven to be a difficult task. One problem has been to develop a check valve that is as insensitive as possible to any strain that develops during manufacture and thereafter. Such strain can cause the check valve to fail to close and to permit the back flow of ink out of the pump chamber, resulting first in the loss of pump efficiency and ultimately in the failure of the check valve to function. Such strain can be caused by numerous factors including an externally applied mechanical load, mechanical interference, chemical attack by the ink causing either shrinkage or swelling, thermal excursion, and continued polymer crystallization after fabrication.
Other problems include check valves opening too slowly or not sufficiently enough so the pump chamber fills too slowly with ink, causing the speed of the printer to diminish and printing through-put to become hampered. Another problem has been designing a check valve that can be pre-loaded shut against its valve seat so that the check valve is insensitive to the actuation speed of the pump. The preload is achieved by axially deforming the center portion of an inexpensive, die cut disk which costs an order of magnitude less than a thermoset part with three dimensional detail derived from compression molding or similar processes.
It will be apparent from the foregoing that although there are many processes and apparatus for transporting ink in ink-jet printers, there is still a need for a check valve in an ink pump that is dependable, low cost, and simple in design.
SUMMARY OF THE INVENTION
Briefly and in general terms, a check valve according to the invention includes a circular valve seat; a resiliently deformable, circular valve disk; and means for axially symmetrically mounting the valve disk with respect to the valve seat.
The check valve disclosed herein solves virtually all of the problems discussed above. Because the design calls for only two parts and the valve disk has detail in only two dimensions, this check valve has low part and assembly costs and is reliable, dependable, robust and simple in design. Its fundamental axial symmetry, the support of the valve disk at a single, fixed point, and use of a central mounting pin make it inherently tolerant to all sources of strain. Also, the design of the check valve exposes a large area to the forward flow of ink which in turn allows the pump chamber to fill more rapidly with ink during operation. Since the valve disk can be pre-loaded shut against its valve seat, the check valve does not have to be shut by pressure from the ink pump, and, thus, the check valve is insensitive to pump actuation speed. Moreover, the valve disk is fabricated from EPDM butyl rubber and the valve seat, from polyethylene so the check valve is thermally stable and is not chemically attacked by the ink used in the printer.
A further feature of this check valve is its low cracking pressure. Cracking pressure is the minimum pressure at which there is non-zero fluid flow through a valve. In check valves that were actually fabricated, the range of cracking pressure was between about 10″ and about 2″ of water column, a negative pressure.
Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
REFERENCES:
patent: 4712574 (1987-12-01), Perrott
Resenex High-Flow Check Valves Catalog # R701 Catalog # R702 Rev. 11/94.
VernayUmbrella Check Valves (Brochure) Vernay Laboratories, Inc. 1995 VUM-0995.
Vernay Duckbill Check Valves (Brochure) Vernay Laboratories, Inc. 1995 VAB-0995.
Hewlett--Packard Company
Le N.
Nguyen Judy
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