Patent Application
20200079080
This patent application claims priority to German Patent Application No. 102018121731.5, filed Sep. 6, 2018, which is incorporated herein by reference in its entirety.
The disclosure relates to an inkjet printer. In particular, the disclosure relates to a method and a device with which the accuracy of the positioning of ink droplets may be advantageously increased.
Inkjet printers may be used for printing to recording media (such as paper, for example). For this purpose, most often a plurality of nozzles are used in order to fire ink droplets onto the recording medium, and thus to generate a desired print image on the recording medium.
A nozzle of an inkjet printer may exhibit differences, from line to line, in the positioning of ink droplets on a recording medium. Such fluctuations of the droplet positioning may lead to a negative effect on the print quality. In particular, line blurriness and/or inhomogeneities in print images may be caused by fluctuations of the droplet positioning.
The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the embodiments of the present disclosure and, together with the description, further serve to explain the principles of the embodiments and to enable a person skilled in the pertinent art to make and use the embodiments.
The exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings. Elements, features and components that are identical, functionally identical and have the same effect are—insofar as is not stated otherwise—respectively provided with the same reference character.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present disclosure. However, it will be apparent to those skilled in the art that the embodiments, including structures, systems, and methods, may be practiced without these specific details. The description and representation herein are the common means used by those experienced or skilled in the art to most effectively convey the substance of their work to others skilled in the art. In other instances, well-known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring embodiments of the disclosure.
An object of the present disclosure includes reducing fluctuations of the droplet positioning of a nozzle of an inkjet printer in order to increase the print quality of the inkjet printer.
According to an aspect of the disclosure, a method is described for improving the positioning of ink droplets of an inkjet printer. The printer includes at least one nozzle, where the actuator of the nozzle may be activated according to a line clock cycle in order to print dots in different lines on a recording medium.
In an exemplary embodiment, the method includes the determination that no ink ejection should be produced from the nozzle in a first line, and that an ink ejection should be produced in a subsequent second line. Moreover, the method includes the activation of the actuator of the nozzle for the first line with an excitation pulse that is configured to produce and/or maintain an oscillation of ink in an ink chamber of the nozzle without an ink droplet being ejected from said nozzle. Furthermore, the method includes the activation of the actuator of the nozzle for the second line with an ejection pulse in order to eject an ink droplet from the nozzle.
In an exemplary embodiment, the ejection pulse is configured such that an ink droplet with a target droplet velocity would be produced by the ejection pulse if the actuator of the nozzle were to have also been activated with an ejection pulse for the preceding first line. In an exemplary embodiment, the ejection pulse is configured such that an ink droplet with a deviating droplet velocity would be produced by the ejection pulse if no excitation of the actuator of the nozzle were to take place in the first line. The excitation pulse may be matched to the ejection pulse such that an ink droplet with a compensated droplet velocity is produced by the ejection pulse since an excitation of the actuator of the nozzle with the excitation pulse has taken place in the first line, wherein the compensated droplet velocity is closer to the target droplet velocity than the deviating droplet velocity.
According to a further aspect of the disclosure, an inkjet printer is described for printing to a recording medium. In an exemplary embodiment, the inkjet printer includes at least one nozzle having an actuator that may be activated according to a line clock cycle in order to print dots in different lines onto a recording medium. In an exemplary embodiment, the printer includes a controller that is configured to determine, based on print data with regard to a print image to be printed, that no ejection should be produced by the nozzle in a first line, and an ink ejection should be produced in a subsequent second line. In an exemplary embodiment, the controller is configured to activate the actuator of the nozzle for the first line with an excitation pulse that is configured to produce and/or maintain an oscillation of ink in an ink chamber of the nozzle without an ink droplet being ejected from said nozzle. In an exemplary embodiment, the controller is configured to activate the actuator of the nozzle for the second line with an ejection pulse in order to eject an ink droplet from said nozzle. The excitation pulse and the ejection pulse may be designed as presented above.
The printer 100 that is depicted in
In the depicted example, the print group 140 of the printer 100 includes two print bars 102, where each print bar 102 may be used for printing with ink of a defined color (for example black, cyan, magenta, and/or yellow, and Magnetic Ink Character Recognition (MICR) ink if applicable). In an exemplary embodiment, the printer 100 includes at least one fixer or dryer that is configured to fix a print image printed onto the recording medium 120.
A print bar 102 may include one or more print heads 103 that are, if applicable, arranged side by side in multiple rows in order to print the dots of different columns 31, 32 of a print image onto the recording medium 120. In the example depicted in
In the embodiment depicted in
The printer 100 also includes a controller 101, for example an activation hardware and/or a processor, that is configured to activate the actuators of the individual nozzles 21, 22 of the individual print heads 103 of the print group 140 in order to apply the print image onto the recording medium 120 depending on print data. In an exemplary embodiment, the controller 101 includes processor circuitry that is configured to perform one or more operations and/or functions of the controller 101, including activating the actuators based on print data, and/or controlling to operation of the printer 100 (including controlling one or more components of the printer 100).
The print group 140 of the printer 100 thus includes at least one print bar 102 with K nozzles 21, 22 that may be activated with a defined line clock cycle or with a defined activation frequency in order to print a line, which line travels transversal to the transport direction 1 of the recording medium 120, with K pixels or K columns 31, 32 of a print image onto the recording medium 120, for example with K>1000. The line clock cycle thus indicates with which timing lines of a print image are printed onto a recording medium 120. The activation frequency thereby typically corresponds to the line clock cycle, so that the nozzles 21, 22 of a print head 103 or print bar 102 may be activated precisely once per line of a print image that is to be printed. In particular, the actuator of a nozzle 21, 22 may be activated (with an ejection pulse) for a line in order to produce an ink ejection for a (non-white) dot in the line, or may be activated in order to produce no ink ejection (for a white dot in the line). In the depicted example, the nozzles 21, 22 are immobile or permanently installed in the printer 100, and the recording medium 120 is directed past the stationary nozzles 21, 22 with a defined transport velocity. The line clock cycle or the activation frequency may be modified accordingly by changing the transport velocity (given a constant dot resolution along the transport direction 1).
The print quality of a print image depends on, among other things, the precision of the positioning of the individual ink droplets of the different nozzles 21, 22 of the inkjet printer 100. The precision of the positioning of an ink droplet thereby depends in particular on the droplet velocity with which an ink droplet is fired by a nozzle 21, 22 onto a recording medium 120. This is presented by way of example in
On its way to the recording medium 120, the ink droplet 131 flies the route 132, which is typically referred to as a nip. At the same time, the recording medium 120 moves past the nozzle 21, 22 with a defined transport velocity along the transport direction 1. As a result of this, the position 133 (along the transport direction 1) at which the ink droplet 131 strikes the recording medium 120 depends on the transport velocity of the recording medium 120 and on the droplet velocity 134 of the ink droplet 131.
Via a deflection 221, 222 of the actuator 220, the ink within the nozzle arrangement 200 may thus be moved and the chamber 212 may be placed under pressure. A defined movement of the actuator 220 thereby produces a corresponding defined movement of the ink, or of the meniscus 210. The defined movement of the actuator 220 is typically produced by a corresponding defined waveform or a corresponding defined pulse of activation signal of the actuator 220. In particular, via a fire pulse (also referred to as an ejection pulse) for activation of the actuator 220, it may be produced that the nozzle 21, 22 ejects an ink droplet 131 via the nozzle opening 201. Different ink droplets 131 may be ejected via different activation signals or ejection pulses to the actuator 220. In particular, ink droplets 131 with different droplet sizes (for example 5 pl, 7 pl, or 12 pl) may thus be ejected. Furthermore, via a pre-fire pulse (also referred to as a pre-ejection pulse) for activation of the actuator 220 it may be produced that, although the nozzle 21, 22 produces a movement of the ink and an oscillation of the meniscus 210, no ink droplet 131 is thereby ejected via the nozzle opening 201.
The oscillation of the meniscus 210 of a nozzle 21, 22 that is produced by a pulse 231 typically has a longer chronological duration than the period duration of one period of the line clock cycle. As a result of this, the meniscus 210 of a nozzle 21, 22 oscillates as a result of an ejection pulse for a dot in a specific line of a print image, even if the actuator 220 of the nozzle 21, 22 is activated with an ejection pulse for a dot of a directly subsequent line of the print image. The ejection pulse for the subsequent line thus produces an oscillation of the meniscus 210 of the nozzle 21, 22 starting from an already present oscillation state of the meniscus 210.
On the other hand, the oscillation of the meniscus 210 of a nozzle 21, 22 decays bit by bit with an increasing number of periods of the line clock cycle if no new pulse 231 for excitation of the meniscus 210 takes place, for example because no non-white dots should be printed. If, after two or more periods of the line clock cycle, an excitation of the meniscus 210 of the nozzle 21, 22 takes place again via an ejection pulse, if applicable an oscillation of the meniscus 210 of the nozzle 21, 22 starting from a rest state of the meniscus 210 is thus produced by the ejection pulse.
An oscillation of the meniscus 210 that is produced starting from an already present oscillation state of the meniscus 210 is typically different than an oscillation of the meniscus 210 that is produced starting from a rest state of the meniscus 210. In particular, the oscillation in the first instance may have a greater or lesser oscillation energy, depending on the phase of the already present oscillation state, than the oscillation in the second instance. As a result of this, the droplet velocity 134 of an ejected ink droplet 131 may also be different for these two instances.
In general, it may thus be maintained that the droplet velocity 134 of an ejected ink droplet 131, and therefore the position 133 of an ink droplet 131 on a recording medium 120, may depend on the oscillation state of the meniscus 210 of a nozzle 21, 22 that the meniscus 210 has when an ejection pulse is produced.
In the uppermost column 31, 32 in
Furthermore, from
The insertion of one or more pauses 251 between two ejection pulses 252 may be considered as a whole-number reduction of the activation frequency or, respectively, slowing of the line clock cycle. The printing of a varying number of “white” dots on a column 31, 32 of a print image may consequently lead to varying droplet velocities 134, and thus to varying droplet positionings. The varying droplet positionings may then lead to visible printing artifacts, in particular given homogeneous grid surfaces over a relatively large area.
Between two ejection pulses 252, a bridging pulse and/or excitation pulse 351 may thus be inserted that keeps the meniscus 210 of a nozzle 21, 22 in oscillation such that the ink droplet 131 that is produced by the following ejection pulse 252 is ejected with a defined target droplet velocity 134. For this purpose, the point in time or the phase 352 of the excitation is preferably adapted to the oscillation of the meniscus 210 in order to maintain the oscillation, in particular with as little energy as possible. For example, the excitation in the example depicted in
For example, the phase 352 of the bridging and/or excitation pulse 351 may be adapted to the oscillation of the meniscus 210 such that the bridging and/or excitation pulse 351 is (at least partially) in phase with the oscillation of the meniscus 210 (and thus supports the oscillation of the meniscus 210). In particular, the bridging and/or excitation pulse 351 may be designed and/or chronologically positioned such that the oscillation of the meniscus 210 is supplied with energy in order to maintain said oscillation of the meniscus 210.
In an exemplary embodiment, the excitation pulse 351 is configured to inject precisely so much energy into a nozzle 21, 22 that the meniscus 210 oscillates and no ink ejection thereby takes place. For example, the excitation pulse 351 may be inserted into pause time periods between dots in order to maintain the oscillation of the meniscus 210 of a nozzle 21, 22. The excitation pulse 351 is thereby not directed toward avoiding the drying of ink in a nozzle 21, 22 given relatively long pause time periods, but rather toward maintaining the oscillations in a nozzle 21, 22. The excitation pulse 351 may be used primarily in the printing or raster areas in order to operate the nozzles 21, 22 of a print head 103 optimally close to an optimal working point in such an instance (i.e. as close as possible to a defined target oscillation energy).
In an exemplary embodiment, the method 400 includes the determination 401 that no ink ejection should be produced by the nozzle 21, 22 in a first line 250, and that an ink ejection should be produced in a subsequent second line 250. In an exemplary embodiment, this is determined based on the print data with regard to a print image to be printed. It may thus be determined that the nozzle 21, 22 should be prepared for an ink ejection to be produced in the subsequent second line 250.
In an exemplary embodiment, the method 400 includes the activation 402 of the actuator 220 of the nozzle 21, 22 for the first line 250 with an excitation pulse 351. The excitation pulse 351 is configured to produce and/or maintain an oscillation of ink in the ink chamber 220 of the nozzle 21, 22 without an ink droplet 131 being ejected by the nozzle 21, 22. In particular, the excitation pulse 351 may be used to introduce oscillation energy into the nozzle 21, 22 in order to prepare the nozzle 21, 22 for the subsequent ink ejection.
In an exemplary embodiment, the method 400 also includes the activation 403 of the actuator 220 of the nozzle 21, 22 for the second line 250 with an ejection pulse 252 in order to eject an ink droplet 131 from the nozzle 21, 22.
In an exemplary embodiment, the ejection pulse 252 is configured such that an ink droplet 131 with a target droplet velocity 134 is produced, at least statistically on average, by said ejection pulse 252 if the actuator 220 of the nozzle 21, 22 has been activated with an ejection pulse 252 in a directly preceding period of the line clock cycle. In other words, given use of the ejection pulse 252, the ink droplet 131 may—at least statistically on average—have the target droplet velocity 134 if ink ejections take place in lines 250 that directly follow one after another.
On the other hand, in an exemplary embodiment, the ejection pulse 252 is configured such that an ink droplet 131 with a deviating (from the target droplet velocity 134) droplet velocity 134 is produced, for example statistically on average, by said ejection pulse 252 if no excitation—meaning in particular a pause 251—of the actuator 220 of the nozzle 21, 22 has taken place in the directly preceding period of the line clock cycle. The deviating droplet velocity 134 is thereby typically lower than the target droplet velocity 134.
The excitation pulse 351 may be matched to the ejection pulse 252 or be dependent on the ejection pulse 251 such that an ink droplet 131 with a compensated droplet velocity 134 is produced, at least statistically on average, by said ejection pulse 252 if an excitation of the actuator 220 of the nozzle 21, 22 with an excitation pulse 351 has taken place in the directly preceding period of the line clock cycle.
In an exemplary embodiment, the excitation pulse 351 is thereby configured such that the compensated droplet velocity 134 is closer to the target droplet velocity 134 than the deviating droplet velocity 134. In particular, the excitation pulse 351 may be matched to the ejection pulse 252, or may be dependent on the ejection pulse 252, such that the compensated droplet velocity 134 deviates by only 20%, 10%, or less from the target droplet velocity 134.
The actuator 220 of a nozzle 21, 22 of an inkjet printer 100 may thus be activated with an excitation pulse 351 in a current line 250 in preparation for an ejection pulse 252 for printing a dot in a subsequent line 250, wherein an oscillation of ink in the nozzle 21, 22 but no ink ejection is produced by the excitation pulse 351. The oscillation that is produced by the excitation pulse 351 is thereby matched to the ejection pulse 252 such that the ink droplet 131 that is ejected by the ejection pulse 252 in the subsequent line 250 has at least approximately a defined target droplet velocity 134. Via the use of excitation pulses 351, the droplet velocity 134 of the ejected ink droplets 131, and thus the droplet positioning, may thus be homogenized.
Via an excitation pulse 351, the oscillating mass of a nozzle 21, 22 may be set into a defined oscillation state at the beginning of a defined period of the line clock cycle in which an ink ejection should be produced, so that an ink droplet 131 with the compensated droplet velocity 134, which corresponds at least approximately to the target droplet velocity 134, is produced by the ejection pulse 252 in the defined period. The defined oscillation state thereby preferably corresponds at least approximately to the target oscillation state that the oscillating mass of the nozzle 21, 22 would exhibit if an ejection pulse 252 were to have been produced instead of the excitation pulse 351. An compensation of the droplet velocity 134 may thus be achieved particularly reliably and precisely via use of an excitation pulse 351.
As presented above, the ink in the ink chamber 212 of a nozzle 21, 22 typically executes a defined oscillation in reaction to an ejection pulse 251. The excitation pulse 351 may be matched to the ejection pulse 252 such that the oscillation of the ink that is produced by an ejection pulse 251 in a period of the line clock cycle is amplified by the excitation pulse 351 in a subsequent period of the line clock cycle, in particular in a directly following line clock cycle. It may this be achieved that, by maintaining an oscillation that was previously produced by an ejection pulse 251, the oscillating mass of the nozzle 21, 22 at least approximately exhibits the target oscillation state at the end of the subsequent period of the line clock cycle, even without an ink ejection being produced (even if it was not an ejection pulse 252 but rather an excitation pulse 351 that was produced in the subsequent period).
The oscillation of the ink that was produced by an ejection pulse 251 may exhibit a defined phase. The excitation pulse 351, in particular a phase 352 of the excitation pulse 351, may then depend on the phase of the oscillation of the ink that has been produced by an ejection pulse 251. In particular, the excitation pulse 351 may be in phase with the oscillation of the ink that has been produced by a preceding ejection pulse 251. The oscillation of the ink that has been produced in a nozzle 21, 22 by an ejection pulse 251 may thus be particularly efficiently maintained in order to achieve the target oscillation state.
The oscillation of the ink that has been produced by an ejection pulse 251 may exhibit a target oscillation energy (as part of the target oscillation state) at the end of a period of the line clock cycle. The excitation pulse 351 may be designed such that the oscillation that is produced or maintained by the excitation pulse 351 in a period of the line clock cycle deviates by 20%, 10%, or less from the target oscillation energy at the end of the period of the line clock cycle.
Via a sequence of one or more excitation pulses 351, it may thus be produced that the oscillation of ink that has been produced by an ejection pulse 252 in a nozzle is maintained until the actuator 220 of the nozzle 21, 22 is activated with a subsequent ejection pulse 252. In particular, a target oscillation state (with a target oscillation energy and/or a target oscillation phase) may thereby be maintained by the sequence of one or more excitation pulses 351. It may thus be efficiently and reliably produced that the ink droplets 131 that are ejected by the subsequent ejection pulse 252 at least approximately exhibit the target droplet velocity 134.
In an exemplary embodiment, the printer 100 includes a plurality of nozzles 21, 22 for a corresponding plurality of columns 31, 32 to be printed to the recording medium 120. The method 400 that is described in this document may be executed for every single nozzle 21, 22 of the plurality of nozzles 21, 22. In particular, the actuators 220 of at least a portion of the nozzles 21, 22 may respectively be activated with an excitation pulse 351 in a period of the line clock cycle in order to prepare the nozzles 21, 22 for an ejection pulse 351 in a subsequent period of the line clock cycle. Alternatively or additionally, the actuators 220 of at least a portion of the nozzles 21, 22 may be activated with an excitation pulse 351 for at least some of the lines 250 of a print image in which the portion of the nozzles 21, 22 is not activated with an ejection pulse 252.
In an exemplary embodiment, the method 400 includes the detection that a homogeneous raster area should be printed by the plurality of nozzles 21, 22, in which the nozzles 21, 22 of the plurality of nozzles 21, 22 should produce an ink ejection for only a fraction of the lines 250 of the raster area. The method 400 that is described in this document may, if applicable, be limited to the use in conjunction with a homogeneous raster area, for example to raster areas that extend over at least 20, 50, 100, 500, or more lines 250 and/or columns 31, 32. The energy efficiency of a printer 100 may thus be increased.
In an exemplary embodiment, a nozzle 21, 22 of the printer 100 is configured to eject ink droplets 131 with a corresponding plurality of different droplet sizes in reaction to a plurality of different ejection pulses 252. Which ejection pulse 252 from the plurality of different ejection pulses 252 should be used for the second line 250 may be determined within the scope of the method 400. For example, which droplet size the ink droplets 131 that are to be ejected for the second line 250 should exhibit may be determined on the basis of the print data. The excitation pulse 351 for activation of the actuator 220 of the nozzle 21, 22 for the first line 250 may then depend on the determined ejection pulse 252. For example, respective different excitation pulses 351 may be used for the different ejection pulses 252. A uniform droplet positioning may thus be produced even given the use of different ejection pulses 252.
Via the measures described in this document, the print quality of a printer 100 may be efficiently and advantageously increased, in particular with regard to streaking and the printing of homogeneous raster areas.
The aforementioned description of the specific embodiments will so fully reveal the general nature of the disclosure that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, and without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.
References in the specification to “one embodiment,” “an embodiment,” “an exemplary embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
The exemplary embodiments described herein are provided for illustrative purposes, and are not limiting. Other exemplary embodiments are possible, and modifications may be made to the exemplary embodiments. Therefore, the specification is not meant to limit the disclosure. Rather, the scope of the disclosure is defined only in accordance with the following claims and their equivalents.
Embodiments may be implemented in hardware (e.g., circuits), firmware, software, or any combination thereof. Embodiments may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact results from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. Further, any of the implementation variations may be carried out by a general purpose computer.
For the purposes of this discussion, the term “processor circuitry” shall be understood to be circuit(s), processor(s), logic, or a combination thereof. A circuit includes an analog circuit, a digital circuit, state machine logic, data processing circuit, other structural electronic hardware, or a combination thereof. A processor includes a microprocessor, a digital signal processor (DSP), central processor (CPU), application-specific instruction set processor (ASIP), graphics and/or image processor, multi-core processor, or other hardware processor. The processor may be “hard-coded” with instructions to perform corresponding function(s) according to aspects described herein. Alternatively, the processor may access an internal and/or external memory to retrieve instructions stored in the memory, which when executed by the processor, perform the corresponding function(s) associated with the processor, and/or one or more functions and/or operations related to the operation of a component having the processor included therein.
In one or more of the exemplary embodiments described herein, the memory is any well-known volatile and/or non-volatile memory, including, for example, read-only memory (ROM), random access memory (RAM), flash memory, a magnetic storage media, an optical disc, erasable programmable read only memory (EPROM), and programmable read only memory (PROM). The memory can be non-removable, removable, or a combination of both.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2018 121 731.5 | Sep 2018 | DE | national |
