Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-04-11
2004-12-21
Nguyen, Lamson (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S046000
Reexamination Certificate
active
06832826
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of ink-drop generators used in inkjet printers. It also relates to a print head and a printer using said ink-drop generator.
BACKGROUND ART
The principle of the inkjet printer is now well-known and has been described, for example, in the American patent No. U.S. Pat. No. 3,373,437 granted to Richard G. Sweet. In this type of printer an ink-drop generator produces drops of ink that are electrically charged then deflected or not deflected by deflecting electrodes to print or not print a downstream substrate. The technology of deflected continuous jets has been widely used in industrial marking applications where inks incorporate volatile solvents and/or pigments for mediums that are difficult to mark where the atmosphere is rendered difficult due to the presence of dust and a variable temperature. The printed widths are small and the outputs are high. A generator of small drops, such as that described in French patent No. FR 2 653 063 (granted to the present applicant), generally comprises a single inkjet created from a pressurized inkjet cavity that has a jet nozzle on one of its surfaces.
The ink cavity also has an elongated cylindrical transducer on a surface opposite that which comprises the nozzle. Said transducer vibrates at a high frequency according to a longitudinal mode and constantly fragments the jet into regular, identical, equidistant droplets. The assembly consisting of the ink cavity, transducer and nozzle plate is called an ink-drop generator. The ink-drop generator is associated with charge electrodes, deflecting electrodes and possibly an ink collector to constitute a print head. One or more print heads can be mounted on the same printer. One or more ink-drop generators can also be assembled to constitute a single print head. For instance, patent application Ser. No. 2 653 063 referred to above discloses a print head comprising at least two modulation bodies and therefore at least two nozzles equipped with means for adjusting each jet and a single ink-collector module with a single pipe for returning the ink to the common circuit. This type of print head offers the possibility of printing large characters at a higher rate than that provided by a head with only one jet. The detailed embodiment of the invention described below also comprises two modulation bodies, which are also called acoustic-wave generators, shakers, resonators or transducers in documents concerning this technology, but each body actuates several inkjets.
In the description of the prior art contained in European patent EP 0 449 929 B1 it is recalled in col. 1, lines 24-25 and 54-58 that, for chambers comprising several jets, each nozzle is positioned facing either its own acoustic vibration generator or a section of a longitudinal acoustic generator whose measurements extend parallel to the line formed by the jet-nozzle assembly. The acoustic generator is supplied with sufficient power to print a vibration with ink in a direction parallel to the jet. The patent then points out in col. 2, lines 1-8 that this configuration of the vibration generator relative to the nozzle plate is not indispensable provided certain conditions of resonance are met. If the conditions of resonance are complied with a single acoustic generator can stimulate the ink passing through a line of nozzles or part of a line of nozzles that has a length considerably greater parallel to the line of nozzles than the size of the acoustic generator in the same direction, for example 5 to 10 times larger. The condition to be complied with is that the vibrating body vibrates virtually only in a longitudinal mode and at a resonance frequency that differs by −10% of the excitation frequency of the natural resonance vibrations in the ink of the cavity between the end of the body and the nozzle plate, the width of the body being smaller than the length of the series of nozzles or the part of the series of nozzles associated with said body.
In this patent the lateral walls of the ink chamber have a cross-section perpendicular to the line of nozzles disposed in a V shape. The tip of the V is turned towards the line of nozzles. The section of chamber comprising the V-shaped walls may be changed to enable the height of the V to be varied depending on the density of the ink and therefore the speed of the sound in the ink used.
Patent application WO 98 51503 also describes an ink-drop generator for an inkjet printer with the following characteristics: the lateral walls of a cavity containing the ink consist of interior and exterior walls. The resistance component of the acoustic impedance of the external walls is such that the external walls passively dampen the vibrations of the interior walls by dispersing the vibrations. The reactive component of the acoustic impedance of the external walls is such that the external walls actively inhibit the vibrations of the internal walls, said external walls thus ensuring that each inkjet sprays drops of ink at the same predetermined distance from each respective nozzle. This type of configuration is used to prevent the nozzle bearing plate from bending in a direction parallel to the inkjet when the printer is used.
The present applicant has filed European patent application EP 0 532 406 A1 concerning multijet modules and the juxtaposition of several modules positioned side-by-side to obtain a large printing width. Much of the detailed description of the embodiment given below repeats the description of the above-mentioned application, particularly everything that relates to the mechanical fastening of print modules to a module assembly beam.
BRIEF DESCRIPTION OF THE INVENTION
As in the examples of embodiments in European patent applications EP 449 929 B1 or EP 0 532 406 A1 referred to above, the invention relates to a multijet print head, i.e. a head in which a cavity containing pressurized ink delivers several jets that are divided into drops by a single resonator for said cavity. As in the embodiment described in European patent application EP 0 532 406 A1, the invention also relates to a print head capable of being mounted such that it is aligned with other heads to constitute a print assembly comprising a large number of jets equidistant from one another capable of simultaneously printing a wide band, for example two or more meters.
The multijet cavities of the prior art described, for example, in patent applications WO 98/51503 or EP 0 449 929 B1 referred to above, enable a single resonator to actuate several jets. However, the end jets, i.e. those leaving the first and last nozzles of the cavity, spray irregularly, produce distorted drops or are formed at variable distances when said end jets are too close to the walls of the cavity.
The inventor of the present invention has used digital simulations to improve the quality of the end jets, for example by using a particular contour of the lateral wall at the nozzle plate, i.e. where said lateral wall is secant to the nozzle plate. Another factor that affects the quality of the end jets is the angle formed by the lateral wall of the cavity with the nozzle plate. The angle is preferably 90° along the entire contour of the lateral wall.
The relation between the vibrating surface of the resonator and the surface of the nozzle plate should also be taken into consideration. The relation between the surfaces should preferably be approximately 1, for example between 3/4and 4/3. The shape of the transitional surface between a resonator housing and the cavity also plays a role. Finally, the relation of the cavity measurements is also important. Each of the factors mentioned above provides an improvement and the combination of all or some of the factors enables the spray quality of the end jets to be indistinguishable from the quality obtained with the central jets.
It becomes possible to position the end-nozzles very close to the intersection of the lateral wall of the cavity with the axial line joining the nozzles. Under these conditions, even though the distance between consecutiv
Imaje
Nguyen Lamson
Pearne & Gordon LLP
Tran Ly T
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