GB2479751A

GB2479751A - Ink blockage determination for multi-jet continuous inkjet printer

Info

Publication number: GB2479751A
Application number: GB1006611A
Authority: GB
Inventors: Daniel John Lee; Anthony Christopher Hunter Hardman
Original assignee: Domino Printing Sciences PLC
Current assignee: Domino Printing Sciences PLC
Priority date: 2010-04-21
Filing date: 2010-04-21
Publication date: 2011-10-26
Anticipated expiration: 2030-04-21
Also published as: GB201006611D0; GB2479751B

Abstract

The invention provides a method of determining a lack of gutter vacuum in the recirculation line 13 of a multi-jet continuous inkjet printer. Individual gutters 12a, 12b are provided for each jet 11, the gutters 12a, 12b being in communication with a common re-circulation line 13. There is a vacuum source, pump 14, creating a vacuum in common re-circulation line 13, Ink sensors 15 are provided on the gutters 12a, 12b for detecting the presence of ink in the gutters 12a, 12b. If ink is sensed in a gutter 12b when not expected, the lack of vacuum in common re-circulation line 13 can be deduced.

Description

IMPROVEMENTS IN OR RELA TING TO CONTINUOUS INKJET PRINTERS

Field of the Invention

This invention relates to continuous inkjet (CIJ) printers and, more particularly, to a continuous inkjet printer having a plurality ofjets.

Background to the Invention

Continuous ink jet printing involves the continuous formation of ink drops from ajet of ink.

Those drops which are to be printed are charged, at the point at which the drops break from the ink jet, and are passed through an electric field. The electric field deflects the charged drops so that they may impinge on a print medium, to form an image. Unused or unprinted drops are not charged and are collected by a recirculation system and are returned to the main ink reservoir. The part of the recirculation system that captures the uncharged drops is commonly called a catcher or gutter. The terminology gutter will be used herein for simplicity.

A number of two-jet Cli systems have been available, for a number of years, and are becoming increasingly popular due to the increase of speed of manufacturing lines, and the requirement of customers that CIJ print speeds increase to match the line speeds. All these systems feature an ink recirculation system or gutter that circulates the unprinted ink back to the printer's ink reservoir.

Two-jet (or dual jet or twin jet) gutter systems operate in a similar fashion to single jet gutter in that a flow of air entrains the unprinted ink in a two-phase flow back to the ink reservoir. When un-deflected, the jets of ink enter the gutter at velocities ranging from 5 to mIs. The gutter systems have to handle a wide variety of fluid densities (between 500 and 3000 kg/m3 for solvents and heavily pigmented inks respectively). The viscosity range is also very spread with solvents having viscosities of as low as 0.5 cP (centipoises) and heavily pigmented inks as high as 15-20 cP, for low temperature applications.

The tubing that connects the print head to the printer, to return ink collected by the gutter, can have a length ranging between 1 and 10 m. This length is usually dictated by the application requirements of the print head needing to be near the product on the production line, and the printer needing to be more accessible at the side of the production line. The source of the airflow, or suction or vacuum, that enables the unprinted ink to be returned to the ink reservoir is, in most cases, a pump. This pump can vary in type (gear, diaphragm or jet pump) and either be coupled to, or be independent of, the pump that supplies pressure to the print head to allow the jet of ink to be formed.

Continuous inkjet printers typically include a sensing facility to detect the presence of ink in the gutter and to communicate this to the printer control system. This facility is used to confirm correct operation of the printer.

Two-jet gutter systems may comprise two independent collectors or pipes that merge into a single line at a point of the returning path to the ink reservoir. This arrangement enables the use of a single recirculation pump. This recirculation pump is typically a vacuum pump which may provide feedback in the form of a tacho frequency output signal proportional to the speed of operation of the pump. The printer control system may monitor this signal to ensure the pump is operating.

It will be appreciated that problems arise if, for any reason, there is a loss of vacuum at the gutter. Such a loss of vacuum could arise from a number of causes including a blockage within the gutter return line or a failure of the recirculation pump. If there is a loss of vacuum the unprinted drops may not correctly enter the gutter, may over-spill the gutter, and may cause damage.

Monitoring vacuum failure by monitoring pump operation is not necessarily effective. A blockage may not be detected by the tacho feedback signal of the vacuum as the pump may continue operating and still create a vacuum against the blockage. Further, if there is a failure of the pump diaphragm, the pump will still turn and therefore generate the tacho feedback signal.

Similarly, a blockage will not always be sensed by the ink sensing facility in the gutter as the sensor(s) may sense the ink which is causing the blockage.

It is an object of this invention to provide a method andlor apparatus relating to continuous inkjet printing which will go at least some way to addressing the problems set forth above; or which will at least offer a novel and useful alternative.

Summary of the Invention

Accordingly, in one aspect, the invention provides a method of determining a lack of gutter vacuum in a return path of a continuous inkjet printer having a plurality of gutters depending from a common collection line, and a vacuum source creating a vacuum in said collection line, said method being characterized in that it comprises providing ink presence sensors on at least two gutters; and processing signals from said ink presence sensors to determine a lack of vacuum in at least one of said gutters.

Preferably said method includes determining if an ink presence sensor is sensing the presence of ink when the presence of ink is not expected.

In a second aspect, the invention provides a continuous inkjet printer configured to sense a blockage in the manner set forth above.

Many variations in the way the present invention can be performed will present themselves to those skilled in the art. The description which follows is intended as an illustration only of one means of performing the invention and the lack of description of variants or equivalents should not be regarded as limiting. Wherever possible, a description of a specific element should be deemed to include any and all equivalents thereof whether in existence now or in the future.

Brief Description of the Drawings

An embodiment of the invention, and modifications thereof, will now be described with reference to the accompanying drawings in which: Figure 1: shows a schematic view of a twin-jet continuous inkjet printhead operating in a first mode; Figure 2: shows a similar view to Figure 1 but with the printhead operating in an alternative mode; and Figure 3: shows a view similar to Figures 1 & 2 but with a blockage present in the ink return line.

Description of Working Embodiment

The invention provides a method of identifying a loss of vacuum in an ink recirculation system of a multi-jet CIJ printer. Whilst the invention could have application to Cli printers having many jets, the particular embodiment described herein relates to a two-jet CIJ printer having a gutter, to collect un-printed ink drops, for each of the jets.

Referring to the Figures, a typical two-jet CIJ printer comprises two drop generators 10, each producing a jet 11 of ink. In the known manner, charge electrodes (not shown) are mounted adjacent to the position at which the individual ink droplets break from the jets and apply a charge to those drops which are to be printed. The ink drops then pass through a deflection field defined by charged plates (not shown), whereupon the charged printing drops are deflected and pass out from the printer on to a substrate to be printed. The uncharged drops pass, un-deflected, through the deflection field and are captured in gutters 12a and 12b. The gutters 12a and 12b feed into a common collection line 13 which is evacuated by a vacuum pump 14. Thus unprinted ink drops collected in the gutters 12a, 12b are circulated back into the ink delivery system (not shown) of the printer.

In the known manner, the gutters 1 2a and 1 2b are provided with ink presence sensors. A common form of ink presence sensor relies on the fact that the ink used in CIJ printers is electrically conductive and this conductivity can be used to indicate the presence of absence of ink. Accordingly, sensing electrodes 15 can be placed in each of the gutters and signals there-from passed to the printer control electronics 16. Conventionally the control system 16 uses this information, for example, to stop the printer if an anomaly is detected such as no ink being present in a particular gutter when a jet is expected, indicating a malfunction of the valves or, perhaps, a misdirected jet. The present invention further processes the signals from the sensing electrodes 15, at start-up, to determine a lack of vacuum in the return line that could lead to over-spilling of the gutters 12a, 12b and any consequential damage which might ensue.

According to the invention, the combination ofjets, and each individual jet, is taken through a cycle to ensure proper vacuum is applying at each gutter.

Referring now to Figure 1, both drop generators 10 are operating, creating two jets 11.

Unprinted drops are collected in the gutters 12a, 12b and are re-circulated by vacuum pump 14. In Figure 2, the drop generator 10 aligned with gutter 12b is switched off. The electrode 15 associated with gutter 1 2b determines that no ink is present in the gutter 1 2b and the control system 16 processes this information and confirms that the printer is operating as intended.

Referring now to Figure 3, the drop generator aligned with gutter 12b is switched off.

However a blockage at 17 in the collection or re-circulation line 13 causes a loss of vacuum which, in turn, causes ink to buildup and force its way into gutter 12b. This ink will be sensed by the electrode 15 associated with gutter 12b and the appropriate signal passed to the control system. Since ink will be sensed in gutter 12b, when not expected, the control system will trigger an alarm that there is a loss of vacuum. The operator is then alerted to investigate the cause.

The method herein described is applied at start-up or after the printer has been idle for a predetermined time. Each drop generator is operated on its own and the ink sensing electrode of the alternate jet interrogated to establish if ink is present.

It will thus be appreciated that the invention, at least in the case of the embodiment described in detail above, provides a simple yet effective method of determining a loss of vacuum, possibly due to the presence of a blockage, in the ink return line of a multi-jet continuous ink jet printer

Claims

Claims 1. A method of determining a lack of gutter vacuum in a return path of a continuous inkjet printer having a plurality of gutters depending from a common collection line, and a vacuum source creating a vacuum in said collection line, said method being characterized in that it comprises providing ink presence sensors on at least two gutters; and processing signals from said ink presence sensors to determine a lack of vacuum in at least one of said gutters.
2. A method as claimed in claim I including determining if an ink presence sensor is sensing the presence of ink when the presence of ink is not expected.
3. A continuous inkjet printer configured to sense a blockage in the manner as claimed in claim 1 or claim 2.