Patent Description:
A CIJ printer typically comprises a printer body and a print head. The printer body contains ink and solvent sources, and an ink system including a controller. The print head includes a drop generator and a gutter for receiving ink drops from the drop generator that are not used for printing. The drop generator is connected to the ink and solvent sources and ink system by ink and solvent feed lines and electrical signal and power lines. The gutter is connected to the ink source by a gutter line. The ink and solvent feed, electrical and gutter lines form a so-called "umbilical" that connects the print head to the printer body.

For reliable operation of a CIJ printer, the ink system, and in particular the drop generator, must be cleaned as part of a shutdown sequence of the printer, to ensure that ink does not dry in the drop generator. Typically, the solvent that is used to reduce the viscosity of the ink is used to clean the ink system.

<CIT> discloses a CIJ printer that draws solvent into a bleed line through a print head, then uses a valve to connect an ink feed line to the bleed line to use a resulting flow of ink into the bleed line to force the solvent in the bleed line through a nozzle of the print head to clean the nozzle. It refers to <CIT>, which is concerned with introducing solvent into an ink feed line normally used for feeding ink to a drop generator, then using a flow of ink through the ink feed line to force the solvent introduced into the ink feed line through a nozzle of the drop generator to clean the nozzle. It is worth noting that <CIT> emphasises, e.g., in its abstract, that when the printer is to be closed down, the nozzle is left filled with solvent.

<CIT> is concerned with preventing solvent from being jetted from a nozzle of a drop generator while solvent flows through the drop generator to clean it. A vacuum source used to draw ink through a gutter line of the drop generator is used to draw solvent out of the drop generator into a bleed line.

According to a first aspect of the invention there is provided a continuous inkjet (CIJ) printer that has a drop generator, an ink source, an ink feed line configured to deliver ink from the ink source to the drop generator, a solvent source, a solvent feed line configured to deliver solvent from the solvent source to the drop generator, a flush valve operable to control a flow of solvent through the solvent feed line, a source of negative pressure, a wash valve operable to connect the ink feed line to the source of negative pressure, and a controller operable to control the valves, the solvent feed line and the ink feed line forming a junction such that, in use of the printer, ink and solvent meet at an interface, wherein the controller is operable, when carrying out a shutdown sequence of the printer, to control the wash valve and flush valve to cause solvent to be drawn into the ink feed line from the solvent feed line to draw the interface along the ink feed line away from the drop generator.

The invention ensures that solvent flowing from the solvent feed line through the drop generator to clean the drop generator is not contaminated with ink from the ink feed line, because when the interface is drawn along the ink feed line away from the drop generator, the ink feed line contains only solvent at the point where the solvent feed line and the ink feed line are joined.

Preferably the solvent feed line is provided with an anti-mixing loop adjacent to the junction of the solvent feed line and the ink feed line.

Where the CIJ printer is provided with the anti-mixing loop, the printer may advantageously have an ink feed valve operable to control a flow of ink through the ink feed line, and the controller may advantageously be operable to control the ink feed valve and the flush valve to cause ink to flow into the solvent feed line to displace the interface along the solvent feed line between the anti-mixing loop and the flush valve.

Preferably the controller is operable to so control the ink feed valve and the flush valve when carrying out a startup sequence of the printer.

Displacing the interface along the solvent feed line between the anti-mixing loop and the flush valve ensures that during operation of the printer, no solvent can enter the drop generator from the solvent feed line. (Solvent entering the drop generator from the solvent feed line might prevent the printer from phasing, i.e., synchronising the formation and charging of ink drops, or reduce the viscosity of the ink, which would affect the trajectories of the ink drops.

According to a second aspect of the invention there is provided a continuous inkjet (CIJ) printer that has a drop generator, an ink source, an ink feed line configured to deliver ink from the ink source to the drop generator, an ink feed valve operable to control a flow of ink through the ink feed line, a negative pressure source, a bleed line configured to deliver ink and/or solvent from the drop generator to the negative pressure source, and a wash valve operable to connect the ink feed line and the bleed line, wherein the wash valve is connected to the ink feed line between the ink feed valve and the drop generator.

The invention enables ink and/or solvent to be removed from a portion of the drop generator between the bleed line and the ink feed line.

Preferably, the CIJ printer includes a print head valve operable to control a flow of ink from the ink feed line into the drop generator. Preferably the print head valve is connected to the ink feed line between the connection to the wash valve and the drop generator.

The inventors have observed that, even where a CIJ printer includes such a print head valve, if solvent and/or ink remains in the drop generator and ink feed line between the bleed line and the print head valve when the printer is shut down, expansion of the ink and/or solvent due to temperature changes in the environment of the printer can cause the ink and/or solvent to drip from a nozzle of the drop generator.

The CIJ printer may advantageously further comprise a bleed valve operable to control a flow of ink and/or solvent in the bleed line and a controller operable to control the bleed valve and to repeatedly open and close the bleed valve when at least one of solvent and ink is present in the bleed line.

The inventors have found that repeatedly opening and closing the bleed valve helps to draw the solvent and/or ink along the bleed line. This is believed to be because the negative pressure source causes the solvent in the bleed line to vaporise, and briefly closing the bleed valve causes the solvent vapour between the bleed valve and the drop generator to condense, and the condensed vapour briefly to move towards the negative pressure source when the bleed valve is opened before it vaporises again.

According to a third aspect of the invention there is provided a method of controlling the operation of a continuous inkjet (CIJ) printer that has a drop generator, an ink source, an ink feed line configured to deliver ink from the ink source to the drop generator, a solvent source, a solvent feed line configured to deliver solvent from the solvent source to the drop generator, a flush valve operable to control a flow of solvent through the solvent feed line, a source of negative pressure, and a wash valve operable to connect the ink feed line to the source of negative pressure, the solvent feed line and the ink feed line forming a junction such that, in use of the printer, ink and solvent meet at an interface, the method comprising, when carrying out a shutdown sequence of the printer, opening the wash valve and flush valve to cause solvent to be drawn into the ink feed line from the solvent feed line to draw the interface along the ink feed line away from the drop generator.

The solvent feed line may advantageously be provided with an anti-mixing loop adjacent to the junction of the solvent feed line and the ink feed line. The ink feed line may advantageously be provided with an ink feed valve operable to control a flow of ink through the ink feed line.

Where the solvent feed line of the CIJ printer is provided with the anti-mixing loop and the ink feed line is provided with the ink feed valve, the method may advantageously further comprise controlling the ink feed valve and the flush valve to cause ink to flow into the solvent feed line to displace the interface along the solvent feed line between the anti-mixing loop and the flush valve.

According to a fourth aspect of the invention there is provided a method of controlling the operation of a continuous inkjet (CIJ) printer that has a drop generator, an ink source, an ink feed line configured to deliver ink from the ink source to the drop generator, an ink feed valve operable to control a flow of ink through the ink feed line, a negative pressure source, a bleed line configured to deliver ink and/or solvent from the drop generator to the negative pressure source, and a wash valve operable to connect the ink feed line and the bleed line, wherein the wash valve is connected to the ink feed line between the ink feed valve and the drop generator, the method comprising opening the wash valve to cause ink and/or solvent to be drawn from the drop generator into the ink feed line.

The CIJ printer may advantageously include a print head valve operable to control a flow of ink from the ink feed line into the drop generator.

Where the CIJ printer includes the print head valve, the method may advantageously further comprise opening the print head valve to cause ink to be drawn from the drop generator and that portion of the ink feed line between the bleed line and the print head valve into the bleed line and/or that portion of the ink feed line between the print head valve and the wash valve.

The CIJ printer may advantageously include a bleed valve operable to control a flow of ink and/or solvent in the bleed line. Where the CIJ printer includes the bleed valve, the method may advantageously further comprise repeatedly opening and closing the bleed valve when at least one of solvent and ink is present in the bleed line.

The invention will now be described, by way of example, with reference to the attached drawing figures, in which:.

The CIJ printer <NUM> of <FIG> comprises a print head <NUM> connected to a manifold <NUM> of a printer body by an umbilical housing an ink feed line <NUM>, a gutter line <NUM>, a bleed line <NUM> and a solvent feed line <NUM>. In operation of the printer, ink is drawn from an ink source in the form of ink reservoir <NUM> and solvent is drawn from a solvent source in the form of solvent reservoir <NUM>. The ink and solvent reservoirs <NUM> and <NUM> are topped up from an ink cartridge <NUM> and a solvent cartridge <NUM>, respectively.

Ink is drawn from the ink reservoir <NUM> by main feed pump <NUM>, which is a gear pump that pushes the ink through a fine system filter <NUM>, after which the ink flow is divided at junction <NUM>. A first component of the ink flow is directed to print head drop generator <NUM>, through ink feed line <NUM>, via a damper <NUM>, ink feed valve <NUM> and further filter <NUM>. A pressure transducer <NUM> located between the ink feed valve <NUM> and further filter <NUM> measures the pressure of the ink in the ink feed line <NUM> to control the main feed pump <NUM>.

The drop generator <NUM> has a nozzle <NUM> that forms a jet of ink that is broken into a sequence of drops, some of which have a charge applied, if they are to be printed drops, the remainder of which are collected and returned to the ink reservoir <NUM> via gutter line <NUM>.

A second component of the ink flow is further divided at junction <NUM> and directed either through a first jet pump <NUM> or through a second jet pump <NUM> before the second component flows are recombined and returned to the ink reservoir <NUM> via return line <NUM>. A branch <NUM> is connected to the output of the first jet pump <NUM> by a viscometer valve <NUM>, which allows a flow of ink to be directed through a viscometer <NUM> for measuring the viscosity of the ink.

In standby mode, when the drop generator is not jetting, the ink feed valve <NUM> is closed and all ink circulates through the jet pumps <NUM> and <NUM> and back to the ink reservoir <NUM>. In this mode the flow of ink is comparatively high while the pressure is comparatively low.

The main feed pump <NUM> develops a pressure at the inlets of the drop generator <NUM> and jet pumps <NUM> and <NUM> of around <NUM> bar, which results in a flow of ink through the drop generator <NUM> of the order of <NUM>/min and a flow of ink through the jet pumps <NUM> and <NUM> of the order of <NUM>/min.

The print head <NUM> includes a print head valve <NUM>, which, as described in greater detail below, allows both ink and solvent to enter the drop generator <NUM>.

Solvent is drawn from the solvent reservoir <NUM> either by vacuum drawn by first jet pump <NUM> or by vacuum drawn by second jet pump <NUM>. First jet pump <NUM> draws a vacuum in bleed line <NUM>, which, in turn, is connected to the interior of the drop generator <NUM> at bleed line junction <NUM>. Bleed valve <NUM> is mounted in the bleed line <NUM>.

Solvent is directed to the drop generator along solvent feed line <NUM>, the solvent feed line <NUM> and the ink feed line <NUM> forming a junction <NUM> inside the print head <NUM>. A flush valve <NUM> is included in the solvent feed line <NUM>, which further includes an anti-mixing loop <NUM> of the type described in <CIT>, the anti-mixing loop <NUM> preventing any flow of ink due to gravity beyond the anti-mixing loop <NUM>. The printer <NUM> includes two further valves, namely a wash valve <NUM> and a makeup valve <NUM>. The wash valve <NUM>, when open, connects the ink feed line <NUM>, between the pressure transducer <NUM> and the further filter <NUM>, to the bleed line <NUM> between the bleed valve <NUM> and the junction <NUM>. The makeup valve <NUM>, when open, connects the solvent reservoir <NUM> to the gutter line <NUM>, such that solvent is drawn from the solvent reservoir <NUM> into the second jet pump <NUM>.

During printing, the ink feed valve <NUM> and printhead valve <NUM> are open allowing ink under pressure to be delivered to the drop generator <NUM>. It will be appreciated that, during printing, wash valve <NUM>, flush valve <NUM> and bleed valve <NUM> are closed. Makeup valve <NUM> is typically closed during printing unless solvent is being added to the ink in the reservoir <NUM> to reduce the viscosity of the ink.

Referring to <FIG>, the first column of the table contains the step numbers referred to in the following description of a shutdown sequence of the printer <NUM>. The second, third, fourth, fifth and sixth columns give the states of the ink feed valve <NUM>, print head valve <NUM>, wash valve <NUM>, bleed valve <NUM> and flush valve <NUM>, respectively, for each step of the shutdown sequence, "<NUM>" indicating an open valve state and "<NUM>" indicating a closed valve state.

At step <NUM>, therefore, the printer is still printing and the ink feed valve <NUM> and print head valve <NUM> are open and the wash valve <NUM>, bleed valve <NUM> and flush valve <NUM> are closed.

At step <NUM>, the shutdown sequence has started. The ink feed valve <NUM> and print head valve <NUM> are closed and bleed valve <NUM> is open. This interrupts the ink jet from the nozzle <NUM> and the vacuum drawn by first jet pump <NUM> draws some of the ink between the bleed line junction <NUM> and the nozzle <NUM> into the bleed line <NUM>.

At step <NUM> the wash valve <NUM> and flush valve <NUM> are opened. The vacuum drawn by the first jet pump <NUM> acts through the wash valve <NUM> to draw solvent into the ink feed line <NUM> from the solvent feed line <NUM>, moving the interface between the ink and the solvent from the solvent feed line <NUM> into the ink feed line <NUM>, between the junction <NUM> and the further filter <NUM>.

At step <NUM>, the print head valve <NUM> is opened and the wash valve <NUM> is closed. The vacuum in the bleed line <NUM> draws solvent from the solvent feed line <NUM> through the junction <NUM> and print head valve <NUM> into the drop generator and into the bleed line <NUM> at the bleed line junction <NUM>. The flow of solvent flushes ink from the print head between the junction <NUM> and the bleed line junction <NUM> into the bleed line <NUM>. It is worth noting that moving the interface between the ink and the solvent between the junction <NUM> and the further filter <NUM> at step <NUM> ensures that there can be no contamination of the solvent used to flush the print head at step <NUM> with ink as the solvent flows through the junction <NUM>, because the ink feed line <NUM> contains only solvent at the junction <NUM>.

After sufficient time to fill the bleed line <NUM> with solvent, at step <NUM> the flush valve <NUM>, print head valve <NUM> and bleed valve <NUM> are closed and the ink feed valve <NUM> and wash valve <NUM> are opened. Ink flows from ink feed line <NUM> through wash valve <NUM> into bleed line <NUM>, forcing solvent to flow through the drop generator from the bleed line junction <NUM> to the nozzle <NUM> and out of the nozzle <NUM>, flushing ink from the drop generator between the bleed line junction <NUM> and the nozzle <NUM>. The ink and solvent jetted from the nozzle <NUM> enter the gutter and are returned by the gutter line <NUM> to the ink reservoir <NUM>.

At step <NUM>, before the ink flowing into the bleed line <NUM> from the ink feed line <NUM> reaches the bleed line junction <NUM>, the wash valve <NUM> is closed and the bleed valve <NUM> is opened. A negative pressure is developed in the bleed line <NUM> and drop generator <NUM>. The small size of the nozzle <NUM> prevents a significant amount of air from being drawn into the drop generator by the negative pressure developed in the drop generator.

At step <NUM>, the bleed valve <NUM> is closed. The negative pressure developed in the bleed line <NUM> draws solvent from the drop generator between the bleed line junction <NUM> and the nozzle <NUM> into the bleed line, leaving the drop generator free of solvent between the bleed line junction <NUM> and the nozzle <NUM>.

At step <NUM>, the ink feed valve <NUM> is closed and the print head valve <NUM>, wash valve <NUM> and bleed valve <NUM> are opened. The vacuum drawn by first jet pump <NUM> acts through wash valve <NUM> and ink feed line <NUM> to draw solvent from the print head between the bleed line junction <NUM> and the print head valve <NUM> along the ink feed line towards the junction <NUM>, leaving the drop generator and ink feed line <NUM> between the bleed line junction <NUM> and print head valve <NUM> free of solvent.

At step <NUM> the print head valve <NUM> and wash valve <NUM> are closed. Emptying the drop generator and ink feed line <NUM> between the drop generator and the print head valve <NUM> of solvent prevents solvent from dripping from the nozzle while the printer is shut down. The bleed line <NUM> contains solvent and air. The bleed valve <NUM> is repeatedly opened and closed to draw the solvent along the bleed line <NUM> to the first jet pump <NUM>. It has been found that "pulsing" the bleed valve <NUM> open and closed in this way is more effective than simply leaving the bleed valve open, possibly because the negative pressure developed in the bleed line <NUM> when the bleed valve is opened causes the solvent to vaporise, and closing the bleed valve increases the pressure in the bleed line and condenses the solvent vapour between the bleed valve and the print head, so that the condensate is briefly drawn towards the first jet pump <NUM> when the bleed valve is opened before being vaporised, so that the solvent moves in a series of steps towards the first jet pump <NUM>.

When the printer is restarted, the bleed valve <NUM> is closed (if not already closed) and the ink feed valve <NUM> and flush valve <NUM> are briefly opened. Ink flows from the ink feed line <NUM> through junction <NUM> into the solvent feed line <NUM>, displacing the solvent along the solvent feed line away from the junction <NUM> until the solvent feed line contains ink from the junction <NUM> to a point between the anti-mixing loop <NUM> and the flush valve <NUM>. At this point, the flush valve <NUM> is closed and the print head valve <NUM> is opened to establish a jet of ink from the nozzle <NUM> of the drop generator <NUM>.

As previously explained, the purpose of the step of priming the solvent feed line <NUM> with ink to a point beyond the anti-mixing loop is to prevent any solvent entering the drop generator while the drop generator is generating ink drops.

The ink feed valve <NUM>, bleed valve <NUM>, wash valve <NUM>, flush valve <NUM>, viscometer valve <NUM> and makeup valve <NUM> are all solenoid valves. The print head valve <NUM> is an armature ported <NUM>:<NUM> valve having minimal dead ended volume within the valve that could trap ink within the valve, trapped ink being likely to cause blockage or sticking of the valve.

A key feature of the invention is the use of the single print head valve <NUM> to deliver both ink and solvent to the drop generator <NUM>, which has advantages both in simplicity and low cost of the ink system.

Claim 1:
A continuous inkjet (CIJ) printer (<NUM>) that has a drop generator (<NUM>), an ink source (<NUM>), an ink feed line (<NUM>) configured to deliver ink from the ink source (<NUM>) to the drop generator (<NUM>), a solvent source (<NUM>), a solvent feed line (<NUM>) configured to deliver solvent from the solvent source (<NUM>) to the drop generator (<NUM>), a flush valve (<NUM>) operable to control a flow of solvent through the solvent feed line (<NUM>), a source of negative pressure (<NUM>), a wash valve (<NUM>) operable to connect the ink feed line to the source of negative pressure (<NUM>), and a controller operable to control the valves (<NUM>, <NUM>), the solvent feed line (<NUM>) and the ink feed line (<NUM>) forming a junction (<NUM>) such that, in use of the printer (<NUM>), ink and solvent meet at an interface, characterised in that the controller is operable, when carrying out a shutdown sequence of the printer (<NUM>), to control the wash valve (<NUM>) and flush valve (<NUM>) to cause solvent to be drawn into the ink feed line (<NUM>) from the solvent feed line (<NUM>) to draw the interface along the ink feed line (<NUM>) away from the drop generator (<NUM>).