GB2128935A

GB2128935A - Ink jet printer

Info

Publication number: GB2128935A
Application number: GB08230046A
Authority: GB
Inventors: Barry Curtis Kockler; Theodore Scott Geiselman; Gerda N Black
Original assignee: Mead Corp
Current assignee: Mead Corp
Priority date: 1982-10-21
Filing date: 1982-10-21
Publication date: 1984-05-10
Also published as: FR2535652A1; GB2128935B

Abstract

An ink jet printer includes a catcher (62) having a catcher plate (64) along the lower portion thereof which is pivotally mounted for rotation about an axis parallel to a row of jet drop streams (12) produced by the ink jet printer print head (10). A charge electrode plate (44), defining a plurality of notched charge electrodes (45), is movable between a drop charging position and a remote position. At start up and shut down of the printer, the charge electrode plate (44) is maintained in its drop charging position when a deflection field is produced by a deflection electrode (50), so as to shield the drops from the deflection field. The catcher (62) is pivoted into a full catch position at start up and shut down so as to catch substantially all of the drops produced by the relatively unstable jet drop streams. <IMAGE>

Description

SPECIFICATION Ink jet printer The present invention relates to ink jet printing and, more particularly, to an ink jet printer in which printer operation and reliability at start up and shut down are enhanced.

Ink jet printers accomplish printing by depositing drops of ink on a print receiving medium in a pattern such that a print image is collectively formed by the drops. Typically, an ink jet printer includes a print head which defines a fluid reservoir to which electrically conductive ink is supplied. A plurality of orifices, arranged in one or more rows, are defined by an orifice plate mounted on the print head and each of the orifices communicates with the fluid reservoir. Ink is forced under pressure through the orifices and emerges as a plurality of fluid filaments. Varicosities are generated in the fluid filaments by mechanical stimulation of the orifice plate or by generating pressure waves which travel through the ink in the fluid reservoir. Fluid filaments are therefore caused to break up into streams of ink drops of substantially uniform size and spacing.

Charge electrodes are positioned beneath the orifice plate and adjacent the tips of the fluid filaments. Electrical charge potentials, selectively applied to the charge electrodes, induce corresponding charges of opposite polarity on the drops as they are formed from the filament tips. The drops then pass downwardly through a deflection field, with the charged drops being deflected by the field and the uncharged drops passing through the field in nondeflected trajectories. The amount of drop deflection is dependent upon a number of factors, including the level of charge carried by the drops.

At the start up of an ink jet printer, the fluid flow through the orifices and the formation of drops from the filaments are irregular and unpredictable. Exceptionally large drops of ink may be formed from the filaments and the trajectories of such drops are largely uncontrolled. As a consequence, there is a possibility that large amounts of ink may be deposited upon the charge electrodes and upon the deflection field electrode structure of the printer. If this occurs, the electrically conductive ink tends to short out the charge electrodes and the deflection electrode structure, and may also interfere with the trajectories of the jets once stable operation is obtained. Additionally, ink may be deposited on the print receiving medium transport and spoil the subsequently printed copies carried by the transport.

The large drops of ink which occur at start up cannot be predictably caught by a catcher in its normal operational position. Even with a catcher arrangement in which the catcher is positioned in line with the non-deflected trajectories of the jet drop streams and deflection of the drops is required for printing, the normal operating position of the catcher is one in which only a relatively small deflection of the drops is needed for the drops to clear the catcher and strike the print receiving medium.

Similar problems are encountered at shut down of the printer. As the pressure of the ink is reduced and fluid flow through the orifices is terminated, the jets once again become unstable and difficult to control.

Accordingly, it is seen that there is a need for a simple, reliable, and compact ink jet printer in which start up and shut down of the printer are facilitated.

According to one aspect of the present invention, an ink jet printer for depositing ink drops on a print receiving medium carried by a print receiving medium transport includes a print head means for generating a row of fluid filaments. The fluid filaments break up into a row of jet drop streams which are directed at the medium transport. A plurality of charge electrodes are mounted on a charge electrode plate. The plate is movable between a drop charging position, in which the charge electrodes are adjacent to and partially surround associated ones of the jet drop streams at the points of drop break up, and a remote position. A means is provided for selectively applying charging potentials to the charge electrodes. A deflection electrode means produces an electrical deflection field in the paths of the jet drop streams so as to deflect charged drops.

A catcher means defines a catcher plate along the lower edge thereof. The catcher means is pivotally mounted for rotation about an axis parallel to the row of jet drop streams for movement between an operating position and a full catch position. When the catcher means is in the operating position, the catcher plate is positioned to catch sufficiently deflected jet drops while permitting drops deflected by the field to a lesser degree, or not at all, to strike the print receiving medium. When the catcher means is in the full catch position, the catcher plate is positioned in the path of undeflected jet drops and extends for a substantial distance on both sides of the row of jet drop streams.

A means for rotating the catcher into its operating position and its full catch position is provided. A means is also provided for moving the charge plate from its remote position into its drop charging position prior to production of the electrical deflection field at start up of the printer, whereby the charge electrodes shield the jet drop streams and thus prevent charging of the drops by the deflection field.

According to another aspect of the present invention, at start up the printer operates according to the steps of: (a) initiating operation of the print head to produce a plurality of jet drop streams while maintaining the charge plate in its remote position and maintaining the catcher in a full catch position, (b) translating the charge plate toward the row of jet drop streams into a position such that the charge electrodes partially surround associated fluid filaments at the points of break up to provide shielding thereof, (c) applying an electrical deflection potential to a deflection electrode so as to produce a deflection field while using the charge electrodes to shield the jet drop streams from the deflection field, (d) pivoting the catcher into its operating position in which deflected drops strike the catcher while charging the drops sufficiently to deflect the drops to the catcher, and (e) initiating selective charging of the drops in the jet drop streams by selective application of charge potentials to the charge electrodes, whereby selected drops are deflected to strike a print receiving medium carried by the print receiving medium transport.

According to yet another aspect of the present invention, at shut down, the printer operates according to the steps of: (a) terminating selective charging of drops in the jet drop streams and charging all of the drops, while maintaining the catcher in its operating position and maintaining the charge plate in its drop charging position such that the charge electrodes partially surround the fluid filaments at the points of drop break up, (b) pivoting the catcher into a full catch position between the print head and the print receiving medium transport such that the catcher extends a substantial distance to either side of the row of jet drop streams so as to catch the drops in the jet drop streams, (c) terminating the application of the electrical deflection potential to the deflection electrode so as to eliminate the deflection field while terminating charging of the drops in the jet drop streams, (d) translating the charge plate away from the row of jet drop streams to its remote position, and (e) terminating operation of the print head and production of the plurality of jet drop streams.

Accordingly, it is an object of the present invention to provide an ink jet printer and method of printer operation in which a catcher may be pivoted into a full catch position at start up, with the charge electrodes being retracted from the vicinity of the jet drop stream so as to prevent contamination of the charge electrodes by unstable streams; to provide such a printer and method in which a deflection electrode does not receive an operating deflection potential until after the charge plate is moved into its operating position, thereby shielding the jet drop streams from charging effects of the deflection field; to provide such a printer and method in which separate electrical actuators are provided for rotating the catcher and translating the charge plate; to provide such a printer and method in which reliability of start up and shut down are enhanced; and to provide such a printer and method in which the sequence and timing of actuation of movement of the catcher and the charge plate may be adjusted.

The invention will now be further described with reference to the accompanying drawings, in which: Figure 1 is an exploded perspective view of the ink jet printer of the present invention; and Figures 2 and 3 are enlarged partial sectional views, taken generally along line 2-2 in Fig. 1, illustrating rotation of the catcher means and translation of the charge plate with respect to the print head.

Reference is now made to Figs. 1, 2 and 3, illustrating the print head means 10 which forms a portion of the ink jet printer of the present invention. A row of fluid filaments which break up into a row of jet drop streams 1 2 are produced by the print head means 1 0.

The streams 1 2 are directed toward a transport, such as conveyor belts 14, which carries a web of paper 16, or other print receiving medium, past the printer.

The print head 10 includes a manifold 20 which defines an elongated fluid cavity or reservoir 21. The print head 10 further includes an orifice plate 22 which defines a plurality of orifices 24 arranged in a row normal to the plane of Figs. 2 and 3. Orifice plate 22 is mounted on the bottom of manifold 20 by an adhesive or, alternatively, by soldering or other appropriate means. The orifices 24 communicate with fluid cavity 21.

Ink supplied to reservoir 21 under pressure emerges from the print head means 10 through orifices 24 as fluid filaments. Electrically conductive ink is supplied to the reservoir 21 via a fluid supply inlet (not shown).

Ink may be removed from reservoir 21 via fluid supply outlet (not shown). A stimulator arrangement (not shown) is provided for causing the fluid filaments to break up into streams of uniformly sized and spaced drops.

Any one of a number of known prior art stimulator arrangements may be used for this purpose.

A charge electrode plate 44 has mounted thereon a plurality of charge electrodes. The charge plate is movable between a drop charging position shown in Fig. 2 in which the charge electrodes are adjacent to and partially surround associated ones of the jet drop streams at the points of drop break up, and a remote position shown in Fig. 3. Preferably, the charge electrode plate includes a nonconductive plate which defines a plurality of notches 45 along an edge of plate 44 which are lined with electrically conductive material, comprising the charge electrodes. A plurality of electrical conductors 46 are printed on the charge electrode plate 44 and are electrically connected to control circuitry via a cable 48. Charge signals from any known source are applied to the charge electrodes via conductors.

A deflection electrode means, including electrode 50, is connected to a source 52 which provides a relatively high electrical deflection voltage. An opposing electrode plate 54 which forms part of the catcher means, is maintained at a different electrical potential and cooperates with electrode 50 to produce an electrical deflection field therebetween. Cavity 58 is connected to a vacuum pump and is maintained at a subatmospheric pressure.

The printer includes a catcher means 62 comprising a catcher plate 64 along the lower portion thereof. The catcher means 62 is pivotally mounted for rotation about an axis, parallel to the row of jet drop streams, between and operating position and a full catch position. In the operating position, shown in Fig. 2, the catcher plate 64 is positioned to receive jet drops which are deflected by the greatest amount, while permitting jet drops deflected by lesser amounts by the field between the plates 54 and 5( > to strike the print receiving medium 1 6. In the full catch position, the catcher plate 64 is positioned in the path of the undeflected jet drops and extends for a substantial distance on both sides of the row of jet drop streams. Fig. 3 depicts the catcher means rotated into its full catch position.

A means for rotating the catcher into its operating position and into its full catch position may comprise a rotary solenoid 66 attached to the catcher by shaft 67. Alternatively, a stepping motor or other electrical actuator may be used for this purpose.

A means for moving the charge plate 44 between its remote position, shown in Fig. 3, and its drop charging position, shown in Fig.

2, includes solenoid 68 attached to plate 44 by shaft 69.

Referring to Figs. 2 and 3, the sequence of movement of the catcher and charge electrode plate at start up of the printer is as follows.

Initially, the catcher 62 and the charge plate 44 are in their full catch and remote positions, respectively, shown in Fig. 3. It should be noted that the catcher plate 64 is pivoted such that it extends along the row of undeflected jet drop streams to either side thereof by a substantial distance. The operation of the print head 10 is initiated while maintaining the charge plate 44 in its remote position and while maintaining the catcher 62 in its full catch position. After the jet drop streams are stabilized, the charge plate 44 is -translated into a position such that the charge electrodes partially surround associated fluid filaments at the points of break up, thus acting as a shield. Next, a deflection potential is supplied to deflection electrode 50, creating an electrical deflection field between electrode 50 and plate 54, which forms a part of the rotatable catcher assembly.

It will be appreciated that the deflection electrode 50 has impressed thereon an electrical potential which tends to produce a strong electrical field upstream at the point of drop formation. If the fluid filaments were left unshielded, this would produce charging of the drops in the jet drop streams to relatively high charge levels. As a result of mutual repulsion, the drops would be scattered, effectively spraying the printer structure and shorting out the high potential printer elements. By shifting the charge electrode plate 44 into its operating position before producing the deflection field, however, the charge electrodes shield the drops from the deflection field and thus preclude charging of the drops by the deflection field.

Next, charging of the drops is initiated, with a relatively large electrical charge being applied to the drops such that the drops are deflected by an amount sufficient to be caught, even after the catcher is pivoted into its operating poSition. Finally, the catcher 62 is pivoted into its operating position, shown in Fig. 2, in which the catcher plate 64 catches drops which are deflected by the greatest amount. The charge plate 44 and catcher 62 are now properly positioned for printing. Selective charging of drops in the jet drop streams by application of charge signals to the charge electrodes may be initiated, producing deflection of the drops to the various desired print positions.

At shut down of the printer, the sequence of steps is substantially the reverse of that utilized at start up. First, the selective charging of the drops in the jet drop streams is terminated, while maintaining the catcher 62 in its operating position and while maintaining the charge electrode plate 44 in its charging position, as illustrated in Fig. 2. All of the drops are charged to a relatively high level such that all of the drops are deflected to the catcher plate 64. The catcher is then pivoted into a full catch position. Next, the electrical deflection potential supplied previously to electrode 50 is removed from the electrode so as to eliminate the deflection field and charging of the drops is terminated.It is important that the charge electrode plate 44 be maintained in its charging position until this field is eliminated so that the jet drop streams continue to be shielded from the deflection field.

The charge electrode plate 44 is then translated into its remote position, illustrated in Fig. 3. Finally, after the charge electrode plate 44 is moved to a position where it is remote from the jet drop streams, the print head 10 is shut down and whatever unstable jets temporarily result are caught by the catcher 62.

While the methods herein described, and the forms of apparatus for carrying these methods into effect, constitute preferred embodiments of this invention, it is to be understood that the invention is not limited to these precise methods and forms of apparatus, and that changes may be made in either without departing from the scope of the invention, as defined in the appended claims.

Claims

1. In an ink jet printer, having a print head defining a plurality of orifices from which fluid filaments emerge to break up into jet drop streams, said jet drop streams being arranged in a row and directed toward a print receiving medium transport, a charge plate including a plurality of open sided charge electrodes for selectively charging drops in said jet drop streams, a deflection electrode positioned to one side of said row of jet drop streams between said print head and said print receiving medium transport, means for supplying an electrical deflection potential to said deflection electrode, and a catcher positioned between said print head and said print receiving medium transport, the method of initiating printer operation, comprising the steps of:: (a) initiating operation of said print head to produce a plurality of said jet drop streams, while maintaining said charge plate in a position remote from said jet drop streams, and while maintaining said catcher in. a full catch position between said print head and said print receiving medium transport and extending a substantial distance to either side of said row of jet drop streams so as to catch the drops in said jet drop streams, (b) translating said charge plate toward said row of jet drop streams into a position such that said charge electrodes partially surround associated fluid filaments at the points of break up to provide shielding thereof, (c) applying said electrical deflection potential to said deflection electrode so as to produce a deflection field while utilizing said charge electrodes to shield said jet drop streams from said field, (d) pivoting said catcher into an operating position in which deflected drops strike said catcher while charging said drops sufficiently to deflect said drops to said catcher, and (e) initiating selective charging of said drops in said jet drop streams by selective application of charge potentials to said charge electrodes, whereby selected drops may be deflected to strike a print receiving medium carried by said print receiving medium transport.

2. In an ink jet printer, having a print head defining a plurality of orifices in which fluid filaments emerge to break up into jet drop streams, said jet drop streams being arranged in a row and directed toward a print receiving medium transport, a charge plate including a plurality of open sided charge electrodes for selectively charging drops in said jet drop streams, a deflection electrode positioned to one side of said row of said jet drop streams between said print head and said print receiving medium transport, means for supplying an electrical deflection potential to said deflection electrode, and a catcher positioned between said print head and said print receiving medium transport, the method of terminating printer operation, comprising the steps of:: (a) terminating selective charging of drops in said jet drop streams and charging all of said drops, while maintaining said catcher in an operating position in which all of said drops are deflected and strike said catcher, (b) pivoting said catcher into a full catch position between said print head and said print receiving medium transport such that said catcher extends a substantial distance to either side of said row of jet drop streams so as to catch the drops in said jet drop streams, (c) terminating the application of said electrical deflection potential to said deflection electrode so as to eliminate said deflection field while terminating charging of drops in said jet drop streams, (d) translating said charge plate away from said row of jet drop streams such that said charge electrodes are remote therefrom, and (e) terminating operation of said print head and production of said plurality of jet drop streams.

3. An ink jet printer for depositing ink drops on a print receiving medium carried by a print receiving medium transport, including print head means for generating a row of fluid filaments which break up into a row of jet drop streams directed at said medium transport, a plurality of charge electrodes mounted on a charge electrode plate, said plate being movable between a drop charging position, in which said charge electrodes are adjacent to and partially surround associated ones of said jet drop streams at the points of drop break up, and a remote position, means for selectively applying charging potentials to said charge electrodes, deflection electrode means for producing an electrical deflection field in the paths of said jet drop streams so as to deflect charged drops, and a catcher means, including a catcher plate along the lower portion thereof, characterized in that pivotally mounted for rotation about an axis parallel to said row of jet drop streams between an operating position in which said catcher plate is positioned to catch sufficiently deflected drops, while permitting jet drops which are deflected less by said field or are undeflected to strike said print receiving medium, and a full catch position in which said catcher plate is positioned in the path of undeflected jet drops and extends for a substantial distance on both sides of said row of jet drop streams, and further characterized in that said printer includes:: means for rotating said catcher means into said operating position and into said full catch position, and means for moving said charge plate from said remote position into said drop charging position prior to production of said electrical deflection field at start up of said printer, whereby said charge electrodes shield said jet drop streams so as to prevent charging of drops in said jet drop streams by said deflection electrode.

4. An ink jet printer according to claim 4 further characterized in that said means for rotating said catcher means comprises a solenoid actuator.

5. An ink jet printer according to claim 3 further characterized in that said means for moving said charge plate comprises a solenoid actuator.

6. An ink jet printer according to claim 3 further characterized in that said catcher means further comprises a plate which cooperates with said deflection electrode means to produce said deflection field.

7. An ink jet printer substantially as hereinbefore described with reference to the accompanying drawings.