Etching a substrate: processes – Forming or treating thermal ink jet article
Reexamination Certificate
1998-12-14
2001-02-13
Gulakowski, Randy (Department: 1746)
Etching a substrate: processes
Forming or treating thermal ink jet article
C216S041000, C347S090000
Reexamination Certificate
active
06187212
ABSTRACT:
TECHNICAL FIELD
The present invention relates to continuous ink jet printers and more particularly to removal of fluid from an ink jet printhead.
BACKGROUND ART
In continuous ink jet printing, ink is supplied under pressure to a manifold that distributes the ink to a plurality of orifices, typically arranged in linear array(s). The ink is expelled from the orifices in jets which break up due to the surface tension of the ink into droplet streams. Ink jet printing is accomplished with these droplet streams by selectively charging and deflecting some droplets from their normal trajectories. The deflected or undeflected droplets are caught and re-circulated and the others are allowed to impinge on a printing surface.
Continuous ink jet printing requires rows of ink drops that are emitted at a high rate of speed and pressure from a stimulated body. Some drops are deflected and recovered for use again. The mix of deflected verses non-deflected drops form text and graphics on a substrate that moves under the stimulated body. To recover the deflected drops, catcher means such as shown in U.S. Pat. No. 4,757,329 have been used. As discussed in the '329 patent, drops are caught by impacting on a flat or sloping surface of the catcher face. The ink then flows down the catcher face and flows around a radius at the bottom of the face to enter the ink return channel of the catcher. The ink return channel is defined by an opening and flow channel between the catcher body and a catcher plate, which is bonded to the bottom of the catcher body. Ink can be removed from the ink return channel by means of a vacuum, as described in U.S. Pat. No. 3,936,135; or by gravity drain, as described in U.S. Pat. No. 4,929,966. The return channel should be configured to insure uniform ink removal across the width of the ink jet array. Furthermore, the flow of air into the ink return channel should be held to a minimum to minimize foam generation in the fluid system and to minimize the disturbance of the ink drops by the air flow. The art is replete with various channel geometries, developed for this purpose, including those shown in U.S. Pat. Nos. 3,936,135; 5,105,205; and 5,469,202. In some, the flow is managed by first forcing the fluid through a narrow gap between the catcher and the catcher plate and then opening up flow channel up to form a larger plenum. By means of the pressure drop associated with the fluid meniscus at the entrance to the ink return channel and the pressure drop produced by the sudden expansion into the larger plenum, these designs control the rate of air flow into the catcher and minimize the effects of pressure variations across the array width produced within the ink return channel. Other configurations make use of a screen at the entrance to the ink return channel. The screen effectively divides up the entrance to the flow channel into numerous small segments. By so doing, the magnitude of the pressures associated with the meniscus at the entrance to the ink return channel is increased due to the sudden expansion of the flow channel into the plenum. Consequently, the existing art has attempted to manage the fluid flow by maintaining a relatively high pressure drop at the entrance to the ink return channel, with a larger plenum having lower pressure drops down stream. In this way, pressure variations produced within the plenum across the width of the array are overwhelmed by the larger entrance pressure drops. This allows the ink to be removed uniformly across the width of the array.
In addition to removing ink uniformly while the printhead is in the operating condition, the catcher means has to be able to remove ink uniformly during the startup sequence when the ink is deflected into the ink return channel by the eyelid. In this condition the ink enters the ink return channel with relatively low kinetic energy. Under such conditions, the high entrance losses of the prior art solutions have tended to provide too much restriction for adequate ink removal.
It is further noted that the manufacturing cost of components is often an issue. For example, in U.S. Pat. 4,857,940, the manufacturing cost of the catcher means was addressed by molding the catcher. While molding can be used for short arrays, for long ink jet arrays the catcher means cannot be molded to the required tolerances. Machining the ink return channel into the catcher can be an expensive operation. To get the desired flow geometries can require complex shapes, which are difficult to machine. This machining of this flow geometry is made more difficult by the need to have a smooth transition to the radius at the bottom of the drop impact face on the front of the catcher. Furthermore, the machining of the ink return channel can produce distortion in the catcher so that the drop impact face and the charge plate bonding surface are no longer flat enough for proper operation.
Furthermore, to securely bond the catcher plate to the bottom of the catcher, it is desirable to roughen the surface of the catcher plate. Typically this is done by grit blasting the catcher plate. Grit blasting however tends to distort the thin plate, which can in turn lead to bond failures.
It is seen, therefore, that a need exists for an improved means for removing fluid from an ink jet printhead. The desired improved means would preferably provide for uniform ink removal without the associated large pressure drops at the entrance of the ink return channel seen in the existing art. Additionally, the desired improved means would preferably provide for improved fabrication of the ink return channel which overcomes problems associated with the prior art fabrication means. Finally, the improved construction would preferably include an improved means for securely bonding the catcher plate to the bottom of the catcher which addresses the bond failures found in the prior art.
SUMMARY OF THE INVENTION
It is the object of the present invention to eliminate the high pressure drops at the entrance to the ink return channel by eliminating the rapid expansion of the flow channel after the entrance section to the return channel. The need for high entrance pressure drops is eliminated by the present invention by utilizing a branching flow channel geometry. This flow channel geometry balances the pressure drops in each branch of the structure and avoids turbulence-producing flow junctions and turns. The present invention eliminates the complex operation of machining the ink return channel into the catcher, by transferring the channel geometry from the catcher to the catcher plate. This not only reduces the manufacturing costs but also improves the rigidity of the catcher. For a long array printer the improved rigidity can be very significant. The invention further reduces the cost of production by utilizing a stress free process to machine the flow channel. This eliminates the need for post machining processes to correct the distortion produced in the part. Furthermore, the present invention provides means to enhance the bonding of the catcher plate to the catcher by using stress free processes to produce the desired surface roughness of the bonding surface. Hence, the present invention solves the problems in the existing art by applying balanced flow geometry using pressure drop as a design advantage, matching design requirements to manufacturing techniques, and using area and shapes to ensure bond strength while removing machining stress and costs.
Other objects and advantages of the invention will be apparent from the following description and the appended claims.
REFERENCES:
patent: 3936135 (1976-02-01), Duffield
patent: 4250510 (1981-02-01), Dressler
patent: 4307407 (1981-12-01), Donahue et al.
patent: 4857940 (1989-08-01), Rueping
patent: 5105205 (1992-04-01), Fagerquist
patent: 5469202 (1995-11-01), Stephens
Bowling Bruce A.
Simon Robert J.
Ahmed Shamim
Gulakowski Randy
Haushalter Barbara Joan
Scitex Digital Printing, Inc.
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