Method of inkjet printing using digital control of jet flow in vicinity of droplets

Abstract

A method of inkjet printing includes the steps of: feeding print media past a printhead; printing onto the print media via a stream of inkjet droplets ejected from the printhead; and generating a jet flow in the vicinity of the stream of inkjet droplets, wherein the jet flow is digitally controlled.

Claims

1. A method of inkjet printing comprising the steps of: feeding print media past a printhead; printing onto the print media via a stream of inkjet droplets ejected from the printhead; and generating a jet flow in the vicinity of the stream of inkjet droplets, wherein the jet flow is digitally controlled.

2. The method of claim 1, wherein the jet flow is digitally controlled in response to a parameter indicative of printing vortex oscillations associated with the stream of inkjet droplets.

3. The method of claim 2, wherein the parameter is a frequency of the printing vortex oscillations.

4. The method of claim 2, further comprising a step of: sensing at least one of: an image printed by the printhead; an air pressure; and an air speed.

5. The method of claim 2, wherein the jet flow is generated using an array of synthetic jet devices.

6. The method of claim 5, wherein a jet vortex oscillation associated with the jet flow is out of phase with a printing vortex oscillation.

7. The method of claim 6, wherein the jet vortex oscillation has a same frequency as a frequency of the printing vortex oscillation.

8. The method of claim 1, wherein the jet flow is controlled dynamically in response to sensed variations in a printing vortex oscillation.

9. The method of claim 1, wherein a distance between a lower surface of the printhead and an upper surface of the print media is in the range of 1 to 5 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic side view of a print assembly according to one embodiment of the present invention.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

(3) Referring to FIG. 1, there is shown, schematically, a print assembly 1 in accordance with one aspect of the present invention. The print assembly 1 comprises a pagewide inkjet printhead 2 ejecting a stream of ink droplets 4 onto print media 6 fed past the printhead in a media feed direction as shown. An array of synthetic jet devices 8 is positioned downstream of the printhead 2 relative to the media feed direction. Each synthetic jet 8 comprises an oscillating membrane 10, which produces a synthetic jet flow 12 through a jet nozzle 14 using the surrounding fluid medium 16 (i.e. air). The oscillating membrane 10 works by expelling fluid through the centre of the jet nozzle 14 during an ‘upstroke’ and then ingesting fluid near the edges of the jet nozzle during a ‘downstroke. Typically, the oscillating membrane 10 is driven by a piezoelectric actuator (not shown), although other actuators (e.g. electromagnetic actuator, mechanical actuator etc.) are also with the ambit of the present invention.

(4) The synthetic jet devices 8 are digitally controlled using suitable control circuitry 18, which receives feedback signals from a sensor 20 positioned in the vicinity of the printhead 2. In the embodiment shown, the sensor 20 is positioned downstream of the synthetic jet 8, although the sensor may be equally positioned between the printhead 2 and the synthetic jet, or even upstream of the printhead. Multiple sensors 20 both upstream and downstream of the printhead 2 are also contemplated within the scope of the present invention.

(5) The sensor 20 may be of any type capable of producing a signal, which is indicative of a frequency of printing vortex oscillations 22 associated with the stream of ink droplets 4. For example, the sensor 20 may be an air pressure sensor detecting changes in air pressure in eth vicinity of the printhead 2. Alternatively, or additionally, the sensor 20 may be an air speed sensor. Alternatively, or additionally, the sensor 20 may be an image sensor detecting print artefacts indicative of the printing vortex oscillations. For example, the image sensor may sense a spacing and/or width of bands or stripes (“woodgraining”) in a printout, which are a characteristic artefact of printing vortex oscillations. In some embodiments, multiple different types of sensor 20 may be used to provide a signal to the control circuitry 18 for controlling actuation of the synthetic jets 8.

(6) The synthetic jets 8 are configured to generate the synthetic jet flow 12 having associated jet vortex oscillations 24, which mitigate the effects of the printing vortex oscillations 12. Optimally, the jet vortex oscillations 24 cancel out the printing vortex oscillations 12 by oscillating out of phase with the printing vortex oscillations at a same frequency. Feedback from the sensor(s) 20 enables the synthetic jets 8 to be digitally controlled so as to generate a synthetic jet flow 12, which dynamically minimizes the effects of the printing vortex oscillations. For example, the synthetic jets 8 may be adjusted dynamically in response to changes in image content, print speed and media thickness.

(7) It is a particular advantage of the present invention that variations in the amplitude and frequency of printing vortex oscillations can be countered using the array of synthetic jets 8. For example, it is known that changes in the PPS (due, for example, to a change in media thickness) will produce different printing vortex oscillations. A PPS of more than 1 mm is known to produce visible woodgraining artefacts due to the increased printing vortex oscillations. The present invention enables a print assembly 1 for printing onto different thicknesses with minimal woodgraining artefacts, irrespective of the PPS. This obviates complex media feed arrangements for maintaining a consistent (small) PPS for different media types.

(8) A further advantage of the present invention is that is obviates cumbersome hydraulic ducting in the print assembly 1 for directing an airflow into a print zone of the printhead 2. The compact synthetic jets 8 may be positioned very close to the printhead 1 (e.g. less than 30 mm, less than 20 mm or less than 10 mm from the printhead) and counter the printing vortex oscillations more effectively than conventional hydraulic ducting arrangements.

(9) It will, of course, be appreciated that the present invention has been described by way of example only and that modifications of detail may be made within the scope of the invention, which is defined in the accompanying claims.