a A jet drop printer includes a reservoir means defining an ink receiving manifold and an orifice means defining a plurality of orifices communicating with the manifold. A plurality of continuously flowing ink streams emerge from the orifices as ink is applied to the manifold under pressure. A drop control means control the trajectories of drops which break off from the streams such that drops are selectively deposited upon a print medium. A support plate supports the reservoir means and the orifice means and is held by a support structure. Piezoelectric transducers are also supported by the support plate and vibrate at a frequency near the natural frequency of the streams, thus causing drops of uniform size and spacing to break off from the streams. A reaction mass is supported by the support plate and is positioned relative to the transducers, the reservoir means and the orifice means such that a vibrational nodal plane passes through the support plate. The support structure is thereby mechanically decoupled from vibrations impressed upon the other elements of the printer.
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4. A jet drop printer, comprising:
reservoir means defining an ink receiving manifold, orifice means defining a plurality of orifices communicating with said manifold to produce a plurality of continuously flowing ink streams emerging from said orifices as ink is applied to said manifold under pressure, drop control means for controlling the trajectories of drops which break off from said streams, a support plate for supporting said reservoir means and said orifice means, support structure for supporting said support plate and said drop control means, vibrating means supported by said support plate for vibrating said reservoir means and said orifice means at a frequency near the natural frequency of said streams without vibrating said drop control means, thereby causing drops to be generated from said streams which are substantially uniform in size, and a reaction mass supported by said support plate and positioned relative to said vibrating means, said reservoir means, and said orifice means such that a vibrational nodal plane passes through said support plate, thereby mechanically decoupling said support structure from the vibrations impressed upon the other elements of said printer said reservoir means and said orifice means.
1. An ink jet print head for generating a plurality of jet streams of ink drops, comprising:
print head support structure, a flexible electrically conductive electrode attached to said support structure, first and second piezoelectric transducer means positioned on opposite sides of said flexible electrically conductive electrode, respectively, fluid reservoir means mounted on said first piezoelectric transducer means, said fluid reservoir means defining an ink receiving manifold therein, an orifice plate connected to said reservoir means and, having a plurality of orifices communicating with said manifold, ink streams emerging from said orifices as ink is applied to said manifold, a reaction mass mounted on said second piezoelectric transducer means on the opposite side of said flexible electrically conductive electrode from said fluid reservoir means, and electrically conductive connector means engaging said reaction mass and said reservoir means and clamping said first and second piezoelectric transducer means and said flexible electrically conductive electrode therebetween, whereby a fluctuating electrical potential placed across each of said first and second piezoelectric transducer means results in mechanical stimulation of said fluid reservoir means and said reaction mass in respective opposite phase relationship, with the flexible electrically conductive electrode means being positioned in a nodal plane therebetween, said stimulation of said fluid reservoir means causing said streams to break up into drops of substantially uniform size and spacing.
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The present invention relates to ink jet printing and, more particularly, to an improved scheme for mechanically stimulating ink fluid filaments to cause the filaments to break up into drop streams of substantially uniform drop size and interdrop spacing.
Jet printers of the type to which the present invention is directed operate by selectively depositing small drops of ink at predetermined points on a print medium to form a print image. The drops of ink are formed from fluid filaments which emerge from small orifices communicating with an ink fluid reservoir in which ink is maintained under pressure. Each fluid filament tends to break apart at its tip to form a stream of ink drops. If no mechanical stimulation were applied, the drops would tend to be somewhat irregular in size and spacing within the stream. As will be appreciated, in order for an image of high resolution to be formed upon a print medium by selective deposition of the ink drops, it is necessary for the drops to be substantially uniform in size and for the interdrop spacing within the stream to be substantially uniform.
One technique utilized to enhance the regularity of drop size and spacing is to position the orifices in a relatively thin, flexible wall of the fluid reservoir. This wall, termed the "orifice plate," is then stimulated mechanically, causing a series of bending waves to travel along the wall. Such a stimulation technique is shown in U.S. Pat. No. 3,739,393, issued June 12, 1973, to Lyon et al in which dampers are positioned at each end of the orifice plate to reduce reflection of the bending waves. This technique, known as traveling wave stimulation, results in substantially uniform drop size and spacing. In a multiple jet printer using this technique, break up of drops along the print head will occur at various times, as the bending waves travel along the orifice plate. The formation of drops in each stream in such a printer is out of phase with respect to the formation of drops in the other streams. Additionally, the selection of orifice plate material for such a printer is drastically limited, since the plate must be sufficiently flexible in order to transmit the bending waves along the complete extent of the print head with sufficient amplitude.
Another approach to stimulation of jet drop break up is shown in U.S. Pat. No. 3,586,907, issued June 22, 1971, to Beam et al. This patent shows a printer in which the entire print head, including the ink manifold structure and orifice plate, is mechanically stimulated together. Such an arrangement will necessarily fatigue the print head mounting structure, since this structure will also experience the vibrations applied to the manifold and orifice plate.
A further approach to filament stimulation is disclosed in U.S. Pat. No. 4,095,232, issued June 13, 1978, to Cha. Using the technique disclosed in this patent, stimulators mounted in the upper portion of the fluid reservoir generate pressure waves which are transmitted downward through the fluid in the reservoir into the individual fluid filaments. Each stimulator includes a pair of piezoelectric crystals which vibrate in phase and which are mounted on opposite sides of a mounting plate which is coincident with a nodal plane. A reaction mass is positioned at the opposite end of the stimulator from a stimulation member which is coupled to the fluid. The reaction mass insures that the nodal plane is properly positioned. Such fluid coupled stimulation may, however, result in reflected plane waves from the orifice plate or other structure, which waves may limit in some instances the stimulation effectiveness of the arrangement.
Another stimulation technique is suggested in U.S. Pat. No. 3,667,678, issued June 16, 1972, to Haskell. In the Haskell patent, a nozzle structure is disclosed in which a relatively long tube defining the nozzle is supported at nodal points. The nozzle is stimulated by means of a magneto-strictive stimulator arrangement. The ink reservoir communicating with the tube, however, is fixed and the magneto-strictive stimulator arrangement is mounted by a separate mounting structure from that supporting the tube. The reaction force applied to the stimulator arrangement will, therefore, be coupled to other 53 52 as ink is applied to the manifold 48 under pressure. The ink streams are arranged along a row which is perpendicular to the plane of the drawing of FIG. 3, such that only one such stream is seen. The row of streams 54 are illustrated in FIG. 4. An ink filament extending from orifice 52, when stimulated mechanically at a frequency close to its natural frequency of drop formation, tends to break up into a series of uniformly sized drops 56.
Charge plate 58 defines a plurality of notches along one edge, with each such notch plated with an electrically conductive material 60 and aligned with a respective one of the streams emerging from the orifice plate 50. Conductive material 60 is connected to charge control circuitry which may comprise a digital computer via an electrical connector. The charge control circuitry supplies a series of charge signals to the material 60 to induce selective charging of the drops which are formed from the ends of the fluid stream. The mechanism by which this is accomplished is disclosed more completely in U.S. Pat. No. 3,701,998, issued Oct. 31, 1972, to Mathis.
The trajectory of the drops 56, thus formed, extends past a deflection electrode 62. As described more completely in U.S. Pat. No. 3,656,171, issued Apr. 11, 1972, to Robertson, charged drops induce a corresponding charge of opposite polarity on the surface of grounded, electrically conductive deflection electrode 62, with the result that the drops which are charged tend to be deflected toward the electrode 62. Thus the charged drops will assume a trajectory which causes them to strike the catching surface of catcher 64.
As seen more completely in FIG. 5, the catching surface 66 of catcher 64 defines a plurality of slots 68 into which drops striking the catcher 64 are ingested. Catcher 64 defines an evacuated cavity into which the caught drops are drawn by means of a vacuum applied through vacuum fitting 70 (FIG. 4). The uncharged drops, however, pass the catcher 64 and strike the print medium 10 at selected points thereon as the print head 12 is moved across the print medium 10.
As seen in FIG. 5, fittings 72 and 74 communicate with manifold 48. Ink is supplied to manifold 48 from an ink supply (not shown) by flexible tube 76. Additionally, a flush fluid may be supplied through tube 76 to the manifold 48 when it is desired to clean the manifold, such as when the printer is being shut down. Ink or flush fluid may be removed from the manifold through fitting 74 via flexible tube 78. Tubes 76 and 78 are sufficiently flexible such that they do not affect substantially the mechanical stimulation of the reservoir means 46 and orifice means 50, as described below.
Reference is now made to FIGS. 6 and 7 which illustrate the stimulation arrangement by which the fluid streams passing through orifices in the orifice plate 50 are stimulated to break up into ink drops of uniform size and spacing. The print head support structure includes plate 14 which is attached to bracket 16. Additionally, the print head support structure includes a non-conductive mounting disc 80 which is held within recess 82 in plate 14 by means of threaded bolts 84 and washers 86. Disc 80 defines an annular groove in which is positioned a flexible, electrically conductive electrode 88. Disc 80 electrically insulates the electrically conductive electrode 88 from the plate 14. Electrode 88 acts as a support plate for supporting a vibrating means, including piezoelectric transducers 90 and 92 which are positioned on opposite sides of the electrode 88.
Electrode 88 additionally supports the reservoir means 46 and the orifice means 50, as well as a reaction mass 94. The fluid reservoir means 46 is mounted adjacent the first piezoelectric transducer 90 on the side of the transducers 90 opposite the flexible electrode 88. Similarly, the reaction mass 94 is mounted on the second piezoelectric transducer 92 on the opposite side of the electrode 88 from the fluid reservoir means 46. It should be understood that the fluid reservoir means 46, the transducers 90 and 92, and the reaction mass 94, are mounted solely by means of the electrode 88 and, with the exception of tubes 76 and 78, do not physically contact with the balance of the printer structure.
The ink in manifold 48 is electrically conductive and is received from an ink supply which is maintained at electrical ground potential. Reservoir means 46 is electrically conductive, as is reaction mass 94. An electrically conductive connector means, including threaded bolt 96, engages the reaction mass 94 and the reservoir means, and clamps the first and second piezoelectric transducers 90 and 92 therebetween. Bolt 96 extends through central openings in the transducers 90 and 92 and in electrode 88 and is electrically isolated from the transducers 90, 92 and electrode 88 by an insulator means comprising a non-conductive sheath 98. The reaction mass 94 and the reservoir means 46 thereby maintain surfaces 100 and 102 of the transducers 90 and 92, respectively, at ground potential.
Electrical conductor 104 (FIG. 6) provides a means for applying a fluctuating electrical potential to the electrode 88. Since surfaces 100 and 102 of the transducers 90 and 92 are grounded, the transducers will be electrically stimulated such that they will cyclically change thickness in response to fluctuations in the potential applied between electrode 88 and surfaces 102 and 100. The reaction mass 94, the reservoir means 46, and the orifice plate 50 will therefore be stimulated mechanically at the frequency of the fluctuating signal applied to conductor 104. The frequency of this signal is selected such that it corresponds to the natural frequency of fluid stream break up. The fluid streams emerging from orifices 52 and orifice plate 50 will, therefore, be stimulated to break up into drop streams consisting of drops of substantially uniform size which are evenly spaced apart.
The mass of reaction mass 94 is carefully selected such that the reaction mass 94 and the portion of the bolt 96 on the reaction mass side of the electrode 88 will provide an acoustic impedance close to that provided by reservoir means 46, orifice plate 50, fittings 72 and 74, and the ink within manifold 48. With such an arrangement, stimulation of transducers 90 and 92 produces opposing vibrations on opposite sides of the electrode 88 which tend to cancel each other in the plane of electrode 88, thereby forming a nodal plane. By this technique, the support structure of the print head is mechanically decoupled from the vibrations impressed upon the reservoir means 46 and orifice plate 50. The support structure, therefore, does not become fatigued from stimulation vibrations and the adjustment bolts for the print head are not vibrated out of their initial adjustment settings. Additionally, the print head transport mechanism operates smoothly, and overall stable operation is enhanced.
With the stimulation arrangement of the present invention the reservoir means 46, the ink within manifold 48, and the orifice plate are vibrated together. This results in stimulation which is substantially uniform along the row of jets. The ink filaments extending from the jets will therefore be substantially uniform in length, thus permitting accurate positioning of the charge plate 58 with respect to the filaments.
While the form of apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention.
Cha, Charles L., Denlinger, George W., Pipkorn, David N., Spyrou, Elias
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| Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
| Mar 23 1981 | The Mead Corporation | (assignment on the face of the patent) | / | |||
| Dec 06 1983 | MEAD CORPORATION THE A CORP OF OH | EASTMAN KODAK COMPANY A NJ CORP | ASSIGNMENT OF ASSIGNORS INTEREST | 004237 | /0482 |
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