Patent Application
20140168322
This invention relates to binary continuous inkjet printers with print heads provided with a multi-nozzle drop generator.
The invention is directed to a printing control method and a printer or print head of a printer using this method.
There are two main categories of continuous jet printers, deflected continuous jet printers and binary continuous jet printers. This invention relates to binary continuous jet printers.
In such a printer, since the jet is continuous, it is necessary to control jet cutting so as to be able to separate the ink required for printing from the ink which is not. Controlling jet breaking enables ink drops to be produced as desired. For each position of the medium, for each nozzle, depending on the pattern to be printed, an ink drop coming from the nozzle should be directed towards the printing medium or conversely towards a recovering gutter.
Different methods are known for performing the selection between drops to be directed to the medium and drops to be directed to the recovering gutter. Two categories of continuous jet printers can be distinguished depending on the way of selecting between printing drops and recovered drops. In a first method, the drops have all substantially the same volumes. In a second method, the drops intended for printing and the drops recovered by the gutter are different from each other with respect to their volumes.
A first example of this first category is described in U.S. Pat. No. 3,373,437 to Sweet et al. Conductive ink drops are evenly formed. The drops, being of the same sizes due to their production mode, are formed at a drop charging electrode. According to the potential applied to the charging electrode at the moment of jet breaking, the drop is electrically charged or uncharged. Deflecting electrodes located downstream of the charging electrodes create an electrostatic field which results in deflecting charged drops whereas uncharged drops are not deflected. This flowpath difference enables to separate the drops intended for printing from drops which are not. In a first alternative embodiment, described for example in U.S. Pat. No. 4,636,808 to Heron, the electrode is both a charging and deflecting electrode. The undeflected drops are used for printing. A known drawback of this method is that it requires a charging electrode for each ejecting nozzle the potential of which should be high or low in synchronism with jet breaking. For that reason, the method according to this first example and its alternative are subject to crosstalks. Crosstalks happened between rows, electrodes of adjacent nozzles or between drops from these nozzles. Drops charged by crosstalks, even though weakly charged, are slightly deflected, which results in printing defects.
To partially make up for printing defects produced by crosstalks from drop to drop, there is provided in a second alternative described in U.S. Pat. No. 4,613,871 to Katerberg, introducing guarding drops between drops intended for printing. The guarding drops and printing drops have the same volumes.
Patent application US 2008/0143766, describes a method for printing a pattern on a medium wherein:
the pass time of a pixel is divided into a plurality of subintervals, and wherein
the subintervals are gathered into blocks of subintervals,
each block is defined as a printing block or a non-printing block.
A pattern is formed on the medium as the ink emitted during the intervals corresponding to the printing blocks is formed into printing drops and as the ink emitted during the subintervals associated with the non-printing blocks is formed into non-printing drops captured by a gutter.
This method allows for the setting of the grey levels of the pattern to be printed.
The device described in patent application EP 1 277 580 is essentially a device for cleaning a printing head. In the description of the operation of the printer to which the cleaning device is applied, it is mentioned that small drops for printing and large drops recovered by a gutter are formed.
The device described in patent application US 2003/0063166 in particular in paragraphs 40-45 in connection with
Patent application US 2011/109677 describes a method applicable to a continuous ink jet printer provided with ejecting nozzles. Small printing drops and large non-printing drops are produced. To improve the placement accuracy of the printing drops on the medium with respect to the method described in patent application US 2008/0231669, a phase shift between pulse trains controlling actuators of consecutive nozzles are varied as a function of the medium rate.
This invention originates from a reflection about the printing rate of a continuous jet printer of the second category.
In a printer of the second category where drops are sorted after formation, depending on their volumes, there are drops of the first category, intended for printing. These drops have substantially the same volumes so as to form impacts of the same dimensions onto the medium. By “substantially”, it is meant that the volume of these drops has a mean value form which neither of the drops deviates by more than 12%. The jet rate from a nozzle is constant, the formation time of one drop of the first category is different from the formation time of one drop of the second category. For a constant running rate Vs of the medium with respect to the printing head, the running time Dp of all the pixels is the same, whether the pixels are white or black.
The inventors have shown that there is a relationship between the rate of the medium, jet rate, printing resolution, printing drop volume, non-printed drop volume and printing rate.
Dp=Dii/Vs=da+kdb=k′db′ (1)
wherein:
Dii is the distance between centres of consecutives pixels;
Vs is the running rate of the medium with respect to the printing head;
da is the formation time of one drop of the first category intended to form a black pixel;
k is a positive integer equal to or higher than 1;
db is the formation time of at least one drop of the second category formed during the running time dr of a black pixel minus the time da, dr=Dp−da;
k′ is a positive integer equal to or higher than 1;
db′ is the formation time of at least one drop of the second category formed for printing a white pixel.
This invention enables, for a same rate of jets, to cover a wide range of media rates Vs.
The invention relates to a printing control method for a multi-nozzle binary continuous ink-jet printer or print head of such a printer for printing a pattern on a printing medium moving with respect to the head, the head comprising:
a multi-nozzle drop generator including
a body including
one or more pressurised chambers each able to receive ink under pressure,
ejecting nozzles in hydraulic communication with a pressurised chamber and each able to eject an ink jet having a rate Vj along the longitudinal axis thereof, the nozzles being aligned along an aligning axis and arranged on a same plane,
actuators, each able to cause, on pulse order, breaking of a jet ejected from a nozzle to form a succession of drops,
the medium having with respect to the head, a rate Vs, the distance between consecutive pixels in the direction of movement of the medium being Dii, wherein:
drops of first category and drops of a second category are formed by jet breaking, the drops of the first category each having a first volume, all the first volumes being substantially equal, the drops of the second category having second volumes not necessarily equal but all the drops of the second category have a volume which is not equal to the volume of a drop of the first category,
the flowpaths followed by the drops of the first and second categories are differentiated by applying to at least one of the drop categories a deflection force able to differentiate the flowpaths of drops of the first category and drops of the second category, the flowpath of drops of the first category intersecting the printing medium and the flowpath of drops of the second category intersecting a gutter for recovering such drops,
a piece of information relating to moments where consecutive pixels to be printed run in a position where they are likely to be printed is created,
for printing each black pixel of the pattern (or a black pixel) which is followed by a white pixel, one drop of the first category and one drop of the second category are formed, the cumulative time for forming such drops of the first and second categories being equal to or higher than the running time of one pixel.
It is set out herein that the piece of information relating to moments when the consecutive pixels to be printed run in a position where they are likely to be printed, is generally provided by printing medium advancement measuring means. These measuring means are coupled to the printing control means. They inform the control means about moments of transition between a current pixel and the next consecutive pixel. The piece of information is generally transmitted as electrical, optical or magnetic pulses, transmitted each time the medium has advanced by a distance of one pixel or a fraction of one pixel. These pulses are also called “cues”.
In the following, drops of the first category are of a smaller volume than drops of the second category. All than can be said in the following is also applicable to the opposite case with the proviso to replace “second category” by “first category” in the different sentences and conversely.
According to a first aspect of the invention, to print a black pixel, one drop of the first category and one drop of the second category are formed, the cumulative time for forming the drop of the first category and the drop of the second category being equal to the running time Dp of the medium from the distance Dii.
The embodiment of a black pixel according to this first aspect can be used as long as the remaining running time dr of the pixel is sufficient to form a drop of the second category.
According to a second aspect, to form a white pixel, a drop of the second category is formed the formation time of which is at least equal to the running time of the medium by a distance Dii. The formation time of this drop can be longer than the running time of a pixel if the white pixel is followed by another white pixel.
When the running rate increases, the remaining time dr after formation of one drop of the first category decreases. For high rates, the time dr can become insufficient to form one drop of the second category. In this case, according to a third aspect, prior to printing a current pixel, it is examined whether the following pixel is a white or black pixel.
If the current pixel is black and the following pixel is white, one drop of the first category is formed for printing the current pixel, and then one drop of the second category is formed, the formation time of these drops of the first and second categories being equal to at least twice the running time Dp of a pixel. This time can be greater if the white pixel is followed by another white pixel. It will be noted that in this case, the cumulative formation time of drops of the first and second categories is longer than the running time of one pixel.
If the current pixel is a black pixel and the following pixel is also a black pixel, drops of the first category are formed for at time equal to the running time of the current black pixel, plus a time between 1 and 2 times the formation time da of one drop of the first category.
Other advantages and characteristics of the invention will appear more clearly upon reading the detailed description made in reference to the following figures wherein:
Elements having similar functions in
It is represented in
The head comprises a so-called multi-nozzle generator 5 with a body 1, including one or more rows of pressurised stimulation chambers 2. For more details about the multi-nozzle drop generator 5, U.S. Pat. No. 4,730,197, for example, may be referred to. For details relating to ink supplies, ink tank and restrictions, explanations given in U.S. Pat. No. 7,192,121 may be referred to.
Each pressurised stimulation chamber 2 is in hydraulic communication with a nozzle 3 via a conduit 4. All the nozzles 3 are aligned along an aligning axis and they are arranged in a same plane 17. These nozzles 3 are generally made in a plate usually called nozzle plate and the underneath surface of which is the plane 17.
Actuators 6 are each mechanically coupled to one of the pressurised chambers 2. The actuators 6 are each electrically coupled or connected to printing control means 13, for example as represented in
The control means 13 receive as an input data 16 about the relative position between the printing head 20 and printing medium 12 and information 14 about the pattern to be printed represented by arrows on the figures. As set out above, the data 16 are one piece of information from which the control means 13 are informed about the beginning and the end of running of one pixel.
The control means 13 includes one or more microprocessors and memories 18. The memories 18 contain a printing driving software and data 14 relating to the pattern to be printed. The control means 13 control sending pulses for jet breaking to each actuator 6.
The printing head 20 further includes a set of electrodes arranged downstream of the multi-nozzle drop generator 5 and laterally offset with respect to the plane containing the axes A of the nozzles 3. This set first comprises a first electrode 7 immediately downstream of the nozzles 3. This electrode is called shielding electrode 7 because it is at the same electrical potential as the ink present in the pressurised stimulation chamber 2. The chamber is called stimulation chamber because jet breaking is achieved through creating by means of an actuator 6 a pressure wave which propagates to the jet through the chamber. Downstream of the shielding electrode 7, is arranged at least one pair of electrodes. The example shown includes two pairs of deflecting electrodes 8, 9 the most upstream of which includes two electrodes 8a, 8b and the most downstream 9 of which includes electrodes 9a, 9b. The electrodes 8a, 8b or 9a, 9b of a same pair are preferably powered in opposite phase by an AC voltage.
A dielectric layer 10i is present between two consecutive electrodes 7, 8a, 8b, 9a, 9b.
Finally, a recovery gutter 11 for the ink not used for printing is arranged downstream of all the electrodes 7, 8a, 8b, 9a, 9b.
The body 1, the actuators 6 and means thereof for coupling and connecting to control means 13, the shielding electrode 7, the deflecting electrodes 8a, 8b, 9a, 9b, the dielectrics 10i, the ink recovery gutter 11 together form the printing head 20.
Another printer that can make use of the control method according to the invention will now be described in relation to
The printer described in relation with
The printing head 20 of this printer differs from the printing head described in relation to
This set is replaced by a conduit W wherein a wind is blown. This wind is the means for differentiating flowpaths of drops of the first and second categories. While in the example represented in
As represented in
The operation of a printing head as described in relation with
The printing head 20 and a printing medium 12 are moving with respect to each other. Jet breakings for forming drops are obtained by sending pulses to the actuators 6. The volume of a drop in the case of the printer represented in
The duration should be small enough for the most downstream part of the jet section which is formed from the moment of breaking due to the first pulse to be upstream of the dielectric layer 10i separating the shielding electrode 7 from the first deflecting electrode 8a. These drops are thus formed at a point where the jet part which will make them after the breaking due to the second pulse has not undergone any electrostatic influence from the deflecting electrodes 8a, 8b; 9a, 9b. Therefore, the flowpath of these drops is undeflected by the deflecting electrodes 8, 9. These non-deflected drops will come and impact the printing medium 12. When the duration between two consecutive pulses applied to a same actuator is longer than the formation time of one drop of the first category and sufficient to form one drop of the second category, the drop of the second category is deflected due to the electrostatic force exerted on it by at least one of the deflecting electrode 8a, 8b; 9a, 9b.
In the printer described in relation with
The wind W arrives transversal to the flowpath of the drops and deflects more drops of the first category than more voluminous drops of the second category. Drops of the second category, the flowpath of which is not much deflected, are recovered by the gutter 11, and drops of the first category the flowpath of which is more deflected will impact a medium 12. In this exemplary embodiment, drops of the first category are also of a smaller volume than drops of the second category, but they are the most deflected drops.
In the case of printers described in relation to
Embodiments of the invention will now be described. Generally, the control method according to the invention is applicable to any binary continuous jet printer wherein a differentiated deflection of the flowpath of drops as a function of volumes thereof occurs. These embodiments are therefore applicable in particular to printers described in relation to
A first embodiment can be used as long as the relative rate of the medium and that of the printing head is lower than a value Vs0. For the value Vs0, Dp=Dii/Vs0 is equal to (1+Rm)da, wherein equation Rm stands for the minimum value which should be assumed by the ratio R of the volume of one drop of the second category to the volume of one drop of the first category so that flowpaths of drops of the first and second categories are markedly differentiated in view of the separation mode of flowpaths. For running rates of the medium higher than Vs0, a second embodiment of the invention is used. This second embodiment can also be used for rates lower than Vs0.
The first embodiment will now be described in relation with
B, and then two black pixels N. There is shown on this same axis X the formation times da of drops “a” of the first category and db, db′ of drops b and b′ of the second category respectively. Drops b are the ones formed during the running time dr=Dp−da, in the course of printing one black pixel. Drops b′ are the ones formed for the running time Dp of one pixel, in the course of printing one white pixel.
In the first embodiment, black pixels are all formed identically. White pixels are also formed identically. It will therefore only be described for this embodiment the formation of a black pixel and the formation of a white pixel.
To form a black pixel, the control means 13 control sending of one drop of the first category, a, the formation time da of which is represented by a jet portion on the axis X. Then, they control the formation of one drop of the second category the time dr=db of which is represented by a jet portion of the axis X. To form a white pixel, one drop of the second category b′ is formed, for at least the entire duration of a white pixel. In the example shown in
When the running rate increases, the time da for forming drops of the first category remains the same since these drops should have the same volume to form impacts equal to each other the diameter of which is a function of the medium nature but remains between 1 and 1.5 times the distance Dii. On the other hand, the allocated times db and db′ to form drops b and b′ respectively of the second category decrease so that the volume of these drops becomes smaller.
In the representation of
Depending on the separation mode of flowpaths of drops of the first and second categories, the ratio R=1.5 of the volumes of drops of the second category b to first category a can be higher or lower than Rm. In the case where this ratio is equal to or higher than Rm, the first mode can, according to the invention, be used, as represented in
The formation times of drops are illustrated in
In the second operating mode, before printing a current pixel, the nature of the next pixel, whether white or black, is examined.
If the current pixel is black, and the following is also black, according to a first alternative embodiment of this second mode, drops of the first category are formed during the running time Dp of the current pixel, plus a time between 1 and twice the formation time da of one drop of the first category.
For a succession of n consecutive black pixels, let us set
(n−1)Dp/da=(q−δ) (1).
In the formula (1):
In the course of running n consecutive current black pixels, (q−1) drops a are formed, and forming a qth drop a is begun. This qth drop a is called a transition drop because the cue showing the end of the black pixel with a rank n−1 is received in the course of formation thereof. At the end of the formation of the transition drop, a last drop will again be formed for printing the next consecutive black pixel. It will thus be seen that the formation time of the drops a, for n consecutive black pixels is equal to the duration (n−1)Dp plus a duration (2−δ)da, that is ((n−1)Dp+(2−δ)da). The number of drops formed for this duration is equal to:
(n−1)Dp/da+Dp/da+δDp/da=(q+1)Dp/da (2)
In the example represented in
In the case represented in
In the second operating mode, if the current pixel is a black pixel and the next pixel is a white pixel, one drop of the fist category is formed to form the black pixel, and the formation of one drop of the second category is begun without being discontinued at the time of transition between the black pixel and the white pixel. To form one drop of the second category, there is thus provided the duration beginning at the end of the formation of the drop of the first category forming the black pixel, and ending at the end of running of the white pixel following the black pixel.
The upper limit of the running rate Vs in operating in this second mode is reached when the volume ratio between drops of second and first categories (dr+Dp)/da becomes equal to or lower than Rm.
By using the second embodiment, the range of running rate Vs is increased since the upper limit changes from a rate for which dr/da=Rm to a rate for which (dr/da+Dp/da)=Rm.
When a print is begun, the medium 12 is moved with respect to the printing head. When the medium reaches a minimum rate Vsm, the printer is switched on according to the first mode. The first mode can be retained as long as the running rate Vs of the medium is such that dr/da>Rm. For this limit and preferably before this limit is reached, the method proceeds to the second operating mode.
The inventors have noted that, at higher rates Vs, printing faults occur. To make up for these faults, for the direct piece of information of position of the medium, is substituted a substituted piece of information obtained the following way. First, it should be noted that the pulse frequency enabling the moment of transition between consecutive pixels to be determined is the order of 0.8 to 3 hundred kilohertz.
For example, for a rate Vs of 5 m/s and a resolution of 254 dpi, that is 0.1 mm per pixel, a frequency of 300 khz enables to provide six pulses per pixel. The frequency of a reference clock from which are built the clocks necessary to operate control means 13 is in the order of several tens of megahertz, for example 32 MHz.
According to this embodiment of the invention, when the running rate of the medium is higher than a threshold, for a direct piece of information of the position of the medium coming from the medium position measuring means, is substituted a piece of information calculated from the piece of information received by these means. In a detailed manner,
a) the instantaneous running time dpi of one pixel is determined. This time is determined from information coming from the means for measuring the advancement of the printing medium 12. Since drops a have always the same formation time, the number of reference clock periods having to be counted to obtain this time is known.
b) The number of periods of the reference clock necessary for obtaining the time da and the instantaneous times dpi and dri is determined.
c) From the times thus determined, a reconstituted piece of information about the running of the pixels, for example as pulses, is formed.
d) The piece of information thus created is used for controlling jet breakings.
e) The reconstituted piece of information of the pixels is used until the next determination of the instantaneous time dpi of running one pixel.
f) Steps a) to e) are periodically repeated.
A substituted piece of position information calculated from the measured piece of position information is preferably used as long as the medium rate is higher than a threshold, regardless of whether the printer operates according to the first or the second mode. The inventors believe that because a clock is used rather than the direct piece of information coming from the means for measuring the position of the medium 12, inconveniences due to vibrations from the medium are avoided.
The printer according to the invention is frequently used for printing a succession of entire patterns. An entire pattern is for example a short message to be printed on packages which run in front of the printing head. The pattern includes for example a nomenclature, a date, a passage time, or other information relating to the identity or traceability of the packaged object. In this case, the control means 13 construct a piece of information about a pattern printing end and a next pattern printing beginning. The time dpi is determined before each printing of an entire pattern and this time is retained throughout the printing time of the next pattern. The inventors have observed that the printing result obtained is better with this method.
It has been seen above that in the second operating mode, it is preferable for a good positioning of the drop forming the last black pixel of a series of black pixels, that the time Dp be equal to an integer of times the time da.
If the rate is such that Dp=(k+z)da, k is an integer and z is an integer between 0 and 1.
Depending on the value of z, it will be chosen to form k drops of a formation time da′ greater than the time da or (k+1) drops with a formation time smaller than the time da.
There is either
Dp=(k+z)da=kda′ avec da′=(k+z)da/k
or
Dp=(k+z)da=(k+1)da″ avec da″=(k+z)da/(k+1)
It will be chosen to produce k or (k+1) drops so as to minimise the absolute value of the deviation percentage between da′ and da″ respectively with respect to da.
When the running rate of the medium varies while being printed to change from a first constant rate to a second constant rate, the running rate Vs will necessarily have values for which the time Dp is not equal to an integer times the time da. Thus, according to an alternative embodiment of the second embodiment, the formation time da′ of drops a of the first category is varied so that the ratio Dp/da′ remains as close to an integer as possible. Let us consider an example wherein the rate Vs decreases between two values, that is a first value Vsk and a second value Vsk+1. At the end values of this variation range, the time Dp is equal to kda and (k+1)da respectively.
Between both values, the time is (k+z)da. z is an number which, during the rate transition, ranges between 0 and 1. At the beginning of the transition, k drops will be continued to be formed per pixel, but these drops will have a greater formation time da′=(k+z1)/k. From the moment when z is greater than z1, (k+1) drops will be formed per pixel but these drops will have a smaller formation time than the rated value da that is da″=da(k+z1)/(k+1). The z1 value of z is preferably that for which the absolute deviation to 1 of the ratio (k+z1)/(k+1) is equal to the absolute deviation to 1 of the ratio (k+z1)/k. Of course, if as a result of the rate variation, k varies by more than one unit, the same operation is made each time k changes to a value k+1 or in case the medium 12 speeds up from a value k to the value k−1.
For example, at the beginning of the rate transition for which Dp=5da to a rate for which Dp=6da, 5 drops will be continued to be formed per pixel at the beginning of the transition but these drops will have a greater volume than the rated volume da of one drop of the first category da′=5.45/5 that is 1.09da, from the rate for which z1=5.45, six drops will be formed but these drops will have a smaller volume than the rated volume da, that is da′=5.45da/6=0.91da.
Thus, with a maximum deviation of the volume of drops of the first category of 15% around the rated value, positioning faults are minimised.
Preferably, when the running time of one pixel is not equal to an integer times the time da, the substituted piece of position information such as defined above to control jet breakings is used.
| Number | Date | Country | Kind |
|---|---|---|---|
| 11 54652 | May 2011 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/059839 | 5/25/2012 | WO | 00 | 2/17/2014 |
| Number | Date | Country | |
|---|---|---|---|
| 61504903 | Jul 2011 | US |
