Patent Application
20120281047
The invention relates to the field of continuous ink-jet printers with a multi-nozzle print head.
It also relates to the print head of such printers.
Multi-nozzle continuous ink-jet printers include a print head. This head includes an ink drop generator, one or more drop charge electrodes and one or more drop deflection electrodes. The ink drop generator includes in particular one or more ink supply conduits, stimulation chambers which are hydraulically connected with ink jet discharge nozzles. In addition the generator includes means for stimulation and one or more gutters for recovering ink ejected by the discharge nozzles and which is not used for printing. The ink arrives under pressure through ink supply conduits until it is inside the stimulation chamber and emerges in the form of an ink jet through each of the discharge nozzles.
The operation is as follows:
A means for stimulation which is mechanically coupled to each stimulation chamber periodically produces a pulse. This pulse causes a local variation in the diameter of the jet present at the nozzle discharge, which is expressed as a break in the jet at some distance from the nozzle. The operation of charge electrodes placed downstream of the nozzle depends on a signal which represents the data to be printed, so that the drops are either electrically charged or not. Charged drops are then deflected by the deflection electrodes. In one printer embodiment it is the charged drops which strike the printed medium, with the non-deflected drops being recovered through the recovery gutter and returned to the ink circuit. In general, in this first mode, referred to as a deflected continuous jet type, drops may be deflected according to different degrees so that the drops coming from a single nozzle can trace a segment that is perpendicular to a direction of movement of the printed medium. The value of the deflection of a drop is adjusted by means for the voltage value applied to the charge electrode, which itself determines the value of the charge given to this drop, or through the value of a voltage applied to a deflection electrode assigned to the discharge nozzle for this drop. An example of such an embodiment is, for example, described in the U.S. Pat. No. 4,210,919 in the name of Aiba. In another embodiment, known as a binary continuous jet, drops are charged or are not charged by charge electrodes depending on the design to be printed. Electrically charged drops are deflected by deflection electrodes placed downstream of the nozzle and charge electrodes. In general, in this embodiment it is the non-deflected drops which strike the printed medium, whereas the deflected drops are recovered through the gutter. In the embodiments that have just been described, the charge and/or deflection electrodes are each coupled to a device for processing the data to be printed which receives a signal carrying the data to be printed. Depending on the data relating to the design to be printed, the device for processing the data to be printed issues voltages to the charge and deflection electrodes whose value decides the path of the drops sent from each nozzle, to the recovery gutter or to the location that they must reach in order to create the design to be printed. Because the voltages applied to the electrodes are relatively high, and also because, for example, a charge electrode A assigned to a nozzle a is very close to a charge electrode B assigned to an immediately adjacent nozzle b, the supply circuits for these electrodes are very close together. This results in electrical crosstalk occurring between these circuits. This results in printing errors.
In one embodiment specific to the Markem-Imaje company, the body of the drop generator of the print head in an inkjet printer is formed of an assembly of several plates held mechanically together by, for example, diffusion bonding or by adhesive. Such bodies are described in detail, for example, in U.S. Pat. Nos. 4,695,854 or 7,730,197, both attributed to Pitney Bowes Inc. The bodies described in these patents are associated with a drop-on-demand printer. In one embodiment of a printer specific to the Markem-Imaje company which may or may not include a drop generator body made up of an assembly of several plates, and to which the invention applies, each stimulation device is electrically coupled to a device for processing the data to be printed which receives the signal carrying the data to be printed. In this embodiment the result of the processing of the printing data is applied to the piezoelectric actuators which are each mechanically coupled to a stimulation chamber, and not downstream of the discharge nozzles, at the charge or deflection electrodes. This means that the electrical supply circuits for these electrodes can be simplified. In an embodiment described, for example, in patent application WO 2007/042530 published on Apr. 4, 2007, in the name of the MARKEM-IMAJE company, the signal is constituted by two pulses which are spaced apart over time to differing degrees depending on the drop one wishes to obtain. It has been observed, however, that after a period of satisfactory operation, printing defects appear. In the initial stage of the research into the causes of the defects, they were attributed to progressive fouling of the charge and deflection electrodes.
It will be seen later that after research and experimentation the inventors discovered that the problem of fouling of charge or deflection electrodes could result in crosstalk between two adjacent chambers. This is why reference is made hereafter to the prior art relating to crosstalk in printers.
In order to resolve crosstalk problems in a drop on demand printer, U.S. Pat. No. 4,521,786 from the Xerox Corporation describes electronics for controlling the piezoelectric actuators in which the voltage level and step duration are programmable. The objective is to ensure that the drop speed and volume of ink ejected are identical for each printed point, irrespective of the design to be printed. These control electronics are complex and are both digital and analogue.
U.S. Pat. No. 5,438,350 by the XAAR Limited company provides minimising mechanical crosstalk in a drop-on-demand printer by selecting a favourable ratio between the flexibility of the walls of the stimulation chamber and the compressibility of the ink contained in the chambers.
U.S. Pat. No. 6,394,363 by the Technology Partnership PLC company relates to a drop-on-demand printing technology based on the mechanical displacement of the nozzle by means for a piezoelectric element surrounding the nozzle. The mechanical crosstalk is reduced by creating a slit between two nozzles which is machined into both the nozzle plate and into the piezoelectric layer. The mechanical deformation which is gradually transmitted by the nozzle plate is thus blocked by the slit through removal of the mechanical continuity.
Patent application EP 1693203 from the Brother Industries Ltd company proposes reduction in mechanical crosstalk between adjacent chambers of a drop-on-demand printer by reducing the mechanical coupling between adjacent chambers through the creation of grooves in the diaphragm, a mechanical component coupled to the piezoelectric system, at the periphery of the stimulation chamber. Thus the diaphragm is freer to undergo deformation, which enhances stimulation whilst reducing the mechanical transmission of forces between chambers, which reduces the mechanical crosstalk.
Patent application EP 1731308 by the OCE Technologies BV company offers a solution for reducing the mechanical crosstalk between adjacent chambers by compensating for the mechanical crosstalk due to the diaphragm with another mechanical crosstalk which occurs through the walls which separate the adjacent chambers, where the two crosstalks are in phase opposition. The resulting volume of ink discharged due to mechanical crosstalk is therefore zero, or greatly reduced, when there is correct dimensioning of the print head.
Patent application EP 1695826 by the Toshiba Tec KK company reveals a method for active compensation of the mechanical crosstalk which is limited to the operation of the piezoelectrics in “Shear Mode”. For a given stimulation chamber by means for which an ink drop is ejected, both walls, which face each other and which are made up of a piezoelectric actuator part, move in an opposite direction to each other in order to maximise the variation in volume for the production of drops. Conversely, the walls of adjacent stimulation chambers not destined to eject drops are moved in the same direction so as to cancel out the variation in volume and thus suppress the mechanical coupling with the adjacent stimulated chamber. In order to achieve movement of the walls this patent envisages electronics which operate analogue switches with several voltage levels.
U.S. Pat. No. 5,801,732 by the Dataproducts Corporation company provides minimising the drop mass and speed distributions in a drop-on-demand printer which result from mechanical crosstalk by offsetting in time the moment at which drops are emitted. The delay is of very short duration compared with the period which results from the drop emission frequency. The consequences of this offset in time on printing quality are deemed to be minor in comparison with the advantages.
U.S. Pat. No. 6,010,202 by the Xaar Technology Limited proposes a chronology for the ejection of specific drops for a drop-on-demand printer whose piezoelectrics operate in “Shear Mode”. In the structure described, the nozzles are gathered together in groups and the stimulation signal is a succession of steps the first of which produces the drop at a given speed, with the following steps cancelling out the residual pressure waves. The step is constructed by an empirical learning approach (trial and error). The major drawback of such a step technology is that it does not cancel out crosstalk in real time (that is, at any given moment), irrespective of the shape of the signals applied to the transducers.
Finally, U.S. Pat. No. 4,381,515 describes a drop-on-demand printer in which the ejection of a drop is controlled by a pulse on a piezoelectric crystal which surrounds a tube, one end of which includes the discharge nozzle. Each piezoelectric crystal is coupled by an electrical supply line to means for generating drop ejection pulses. In order to reduce the mechanical crosstalk between the stimulated tube and a tube adjacent to the latter, a resistance is introduced between a first supply line and a second supply line, where these first and second lines supply the piezo-electrics of tubes which are adjacent to each other. Thus electrical crosstalk is created between each of the lines which supply the crystal of any tube whatsoever and each of the lines which supply a crystal arranged on a tube which is adjacent to the said any tube. According to this patent U.S. Pat. No. 4,381,515, it has been determined that crosstalk may be positive or negative. In the case of positive crosstalk, the speed of a drop ejected by an adjacent tube is increased, and is conversely decreased in the case of negative crosstalk. Depending on whether the crosstalk is positive or negative, the link resistance is placed upstream or downstream of the crystal. The upstream-downstream direction is the direction of circulation of the control pulses.
The solutions proposed above are all applied to drop-on-demand printers.
The purpose of the invention is to improve both the print quality and autonomy of printers which use continuous jet technology.
The research into the origin of defects revealed gradual fouling of the charge and deflection electrodes. In order to determine the origin of the contamination, the inventors observed in detail the straightness of the jets at the nozzle discharge and the formation of any satellites during the break up of the jet into drops. These observations on the straightness and on the break up of jets allowed straightness defects to be discounted. It was observed, however, that in normal operation, the break up of the jets occurred at unforeseen locations and in an erratic manner. It was observed that erratic jet break up often occurs on a jet next to a stimulated jet, but not always at the same distance from the nozzle. Then the influence of stimulation of a chamber on the break-up distance of a jet emerging from a nozzle which is hydraulically linked to a chamber adjacent to the stimulated chamber was investigated. It was observed that the break up distance of a jet emerging from a chamber adjacent to the stimulated chamber was modified. The jet break-up distance for the chamber adjacent to the stimulated chamber becomes smaller than the natural break-up distance. The break-up distance for this same jet when it is stimulated at the same time as that of an adjacent chamber becomes greater than the expected break-up distance in the case of stimulated jet. In both cases (with the adjacent chamber jet being stimulated or not stimulated) the break-up distance does not occur at the expected distance. The crosstalk between ink distribution nozzles is a known phenomenon in drop-on-demand printing. As explained above, the drop generator body used in the Markem Imaje continuous jet printer is of similar construction to that described in U.S. Pat. Nos. 4,695,854 or 4,730,197, both attributed to Pitney Bowes. These bodies do not exhibit crosstalk in drop-on-demand use whereas for a drop-on-demand printer the stimulation energies for a chamber are much greater than the energy used to modify the jet break-up distance. In drop-on-demand printers the energy sent to a chamber actuator must be sufficient not only to produce a jet from a drop from the nozzle, but also to provide it with a sufficient speed to project the drop onto a printed medium. In continuous jet technology, the purpose of stimulation is simply to produce an acoustic wave, which, by disturbing the jet will cause surface undulation of the jet in which the depression must be of sufficient depth to break up the jet. Thus, for a given drop generator, the stimulation energy required to eject a drop and to give it a desired speed is much greater than the energy required simply to break up a jet emerging from the nozzle. In the present case, the body of the print head used is approximately constructed like that of the drop-on-demand printer print head described in the U.S. Pat. No. 4,730,197 already cited. The inventors felt however that paradoxically, due to the low stimulation energies of their continuous jet printer, weak crosstalk which would remain unnoticed in a drop-on-demand printer would be sufficient to disturb the operation of a continuous jet printer. By examining problems associated with crosstalk, the inventors observed that four different physical phenomena could be the cause:
1/a phenomenon of a hydraulic nature, hereafter referred to as hydraulic crosstalk, in which the stimulation of a deliberately stimulated chamber is transmitted to adjacent chambers through a common ink supply reservoir. Transmission therefore occurs through the ink.
2/a phenomenon which is mechanical in nature, hereafter referred to as mechanical crosstalk, in which mechanical deformation of the walls of a stimulated chamber, in particular the wall formed by the mechanical element, for example a conduit wall linked to a discharge nozzle coupled to the electromechanical actuator, is propagated through the mechanical structure to adjacent conduits.
3/a phenomenon which is thermal in nature, hereafter referred to as thermal crosstalk, in which the heating of a chamber actuator due to the high frequency of stimulation of this actuator is propagated to chambers adjacent to the frequently stimulated chamber, whilst modifying the properties of the ink, for example its viscosity or the speed of sound in this ink.
4/a phenomenon of an electrical nature, hereafter referred to as electrical crosstalk, in which the generally very dense connections produce interferences in the electrical lines in which the supply signals are supplied to the actuators in-drop on-demand printers or to electrodes in continuous ink jet printers.
In the present case the study has shown that the predominant crosstalk was probably mechanical.
Several solutions have already been proposed for preventing or limiting mechanical crosstalk. A few of these solutions have been described above in the paragraph relating to the prior art.
After recognising that erratic drop formation at unexpected locations could result from very weak mechanical crosstalk between adjacent stimulation chambers, the inventors have corrected this crosstalk by applying electrical compensation correction of the mechanical crosstalk.
Thus, in one aspect, the invention relates to a continuous inkjet printer which includes a print head which includes:
It is specified that there is a single actuator per stimulation chamber; similarly there is one stimulation line per actuator and each chamber is hydraulically linked to a single nozzle.
It will be noted that the means for compensating for mechanical crosstalk between adjacent chambers may be located at the printer, for example at the device for processing the data to be printed, or at the print head.
This means that the invention also relates to a print head for an inkjet printer which includes:
In one aspect, the means for compensating for mechanical crosstalk between adjacent chambers include passive coupling components of impedance Z2 between stimulation lines supplying actuators of adjacent chambers.
The passive coupling components form a voltage divider bridge made up on the one hand of the impedance Z1 of the stimulation line and on the other hand by the impedance Z2 which is electrically coupled between two stimulation lines supplying adjacent chambers.
The passive coupling components may be chosen from a group which includes, for example, a resistance, a capacitance, a resistance and a capacitance in series, a resistance and a capacitance in parallel.
In another aspect, the means for compensating for mechanical crosstalk between adjacent chambers includes two coupling Zener diodes between lines supplying actuators of adjacent chambers, where the two diodes have opposite passing directions.
The invention also relates to a method for reducing the consequences of mechanical crosstalk between adjacent stimulation chambers in the print head of a continuous inkjet printer which includes
When the adjacent chamber is itself stimulated, the compensation and stimulation pulses are added together.
It became clear during the investigation that the relative value of the compensation pulse in relation to the stimulation pulse is, for a given material, a function of the thickness of the separation walls between consecutive stimulation chambers. By necessity, the thickness between consecutive chambers decreases when the gap between consecutive nozzles decreases. The distance between nozzles controls the number of dots per inch (DPI) for the printer.
In one embodiment the crosstalk compensation pulse has a peak amplitude which is such that the break-up distance of the jet from a nozzle which is hydraulically connected with a chamber adjacent to the stimulated chamber is sufficiently great for a drop formed at the break up point of the jet to have a trajectory which is not modified by the effect of the charge and deflection electrodes.
In one embodiment the crosstalk compensation pulse has a peak amplitude which is such that the break-up distance of the jet from a nozzle which is hydraulically connected with a chamber adjacent to the stimulated chamber is sufficiently great for it to be in a zone where an electric field of the charge and deflection electrodes is too small to have an influence on the trajectory of a drop formed at the break-up point.
Other characteristics and advantages of the invention will emerge more clearly on reading the detailed description, which is given for illustrative purposes only and is in no way restrictive, with reference to the appended drawings in which:
Details of embodiments will now be described.
In the embodiment which is described below, the body 1 of the drop generator for the print head 70 is made up of a stack of plates assembled together, for example, by diffusion bonding under pressure or using adhesive as described in U.S. Pat. No. 4,730,197. For further details on this embodiment of the body, and in particular for details relating to the ink inlets, ink reservoir and to the restrictions, reference can be made to the explanations given in that patent. The present description will be limited to a description of elements which are of use in understanding the invention.
Piezoelectric actuators 6 are arranged on the body 1 above the diaphragm 5. Each actuator is mechanically linked to a part 11 of the diaphragm, for example using adhesive. Each actuator 6 is this above a chamber 3. In the example shown, the chambers 3 and therefore the actuators 6 are arranged in two parallel rows, a first row and a second row. Although this arrangement is not compulsory, it advantageously allows the distance between consecutive nozzles 30 to be reduced, as has already been explained in connection with
In other embodiments which include only one row of chambers, two consecutive nozzles of a line are hydraulically connected respectively to consecutive chambers in a row of chambers.
In the rest of the description and the claims, adjacent chambers are consecutive chambers in the same row of chambers.
The operation of the print head is itself known and is described in detail in, for example, the patent application WO 2007/042530 published Apr. 4, 2007 in the name of the MARKEM-IMAJE company. What is important to note about the present invention is that in the absence of a pulse to the actuator 6 of a chamber 3, the jet breaks up at a distance Ln from the nozzle 30, the so-called natural break-up distance of the jet. This distance Ln is shown at the discharge from the nozzle 30i. For correct operation the natural break-up point must be located downstream of the line DD. When a pulse is received, the distance from the nozzle of the jet break-up is reduced. Thus in the embodiment of continuous inkjet printers specific to the Markem-Imaje company, the jet break-up distance La for a drop intended for printing is controlled by the characteristics of a stimulation pulse signal received by the piezo-electric actuator that is operationally connected to the stimulation chamber from which this jet is issued. The distance La between the discharge from a nozzle 30 and the break-up point of the jet is shown at the nozzle discharge 30a.
Additional explanations relating to this known operation will now be given. First of all it is important to remember that in the printer described here, from the Markem-Imaje company, selection between drops intended for printing and drops which go towards the recovery gutter is achieved by control of the break-up point of the jet. The investigation carried out by the inventors has shown that when, for example, the actuator 6a receives a pulse, part 11 of diaphragm which covers the chamber 3a is deformed with an amplitude A as indicated by a curve represented as a broken line in
In order to correct the operation that was thus observed, the inventors corrected the control of the stimulation electrodes 8. For each command pulse for an actuator 6a of a stimulated chamber 3a, an electrical pulse to compensate for mechanical crosstalk is sent to each of the actuators 6b, 6c of the chambers 3b, 3c adjacent to the stimulated chamber 3a.
A method for determining the relative value of the peak amplitude of the pulse to be sent to an actuator of an adjacent chamber to compensate for the mechanical crosstalk will now be described with reference to
The ordinate in
The absolute value of 3.2 volts stated in connection with
In a first preferred embodiment represented in
This circuit is formed on a printed board 19. This embodiment on a printed circuit is in no way compulsory, but is convenient when the body 1 of the drop generator is made up of a stack of plates. The actuators 6 are arranged on the printed circuit so that when the printed circuit is returned over the flat diaphragm 5 of the body 1 of the drop generator, and put in place on this diaphragm, the actuators 6 occupy the location that they must occupy above each of the chambers 3 of the body 1. The electrical command lines 91, 92 . . . 9n respectively couple each output 71, 72, . . . 7n-1, 7n of a device for processing data to be printed 7 to an electrode 8 supplying an actuator 6. When the printed circuit 19 is put in place, each electrode 8 forms with the upper conductive surface of the diaphragm 5 opposite it, made for example of steel, a capacitance 14 represented in
In accordance with the specific mode of the invention described here, a passive component, for example a resistance R1, is incorporated in each line 9. In this embodiment the incorporation of the resistance R1 is not compulsory. In particular, if the line impedance Z1, which results in particular from the circuits upstream of the transmission lines 9 is quite large. Furthermore each line 9 which supplies a chamber actuator is electrically connected by a resistance R2 to each line 9 supplying an actuator arranged on a chamber adjacent to the said chamber. The assembly R1, R2 forms a voltage divider bridge. Thus when a voltage V is applied to an actuator of a stimulated chamber, a lesser voltage V′ is applied to each chamber actuator adjacent to the said stimulated chamber. Determination of the value of the reduction ratio R2/R1=V′/V has been explained above in connection with
This embodiment is particularly simple and meets the desired compensation criteria. Thus,
and finally when two stimulated chambers are adjacent to a given non-stimulated chamber, a compensation pulse is sent to the actuator of the non-stimulated chamber located between the two stimulated chambers, whose peak value is double the peak value of a compensation pulse received when a single adjacent chamber is stimulated. Thus the crosstalk from two stimulated chambers adjacent to a given chamber is compensated for.
It should be noted that the sending of compensation pulses such has just been described may be achieved by means for software available to those working in the field. The device for processing of data to be printed 7 includes in general a processor that just needs to be processed for this purpose. In this case the print head does not include means for compensation since these means are included in the printer upstream of the print head.
The circuit represented in
In an alternative embodiment to those modes shown in
In the mode represented in
In a third embodiment, represented in
The graph shown in
The various embodiments of the invention allow operating times for the printer to be increased without undesirable fouling of electrodes, and therefore operational autonomy can be increased.
Furthermore the printing quality is improved since the distribution of drops intended for printing is better controlled.
| Number | Date | Country | Kind |
|---|---|---|---|
| 09 58276 | Nov 2009 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/067937 | 11/22/2010 | WO | 00 | 5/21/2012 |
| Number | Date | Country | |
|---|---|---|---|
| 61290321 | Dec 2009 | US |
