In a print device an image is printed on a print medium. Typically a print, device, such as an inkjet printer, comprises one or more print heads that, are arranged to deposit a printing fluid such as ink upon the print medium. The one or more print heads are typically controlled by a print controller. Such a print controller receives an input image to be printed and generates a number of signals to control the print device. Based on these signals the printing fluid is ejected from the one or more print heads. Many print devices incorporate some form of relative movement between the print medium and the one or more print heads so that printing fluid is deposited onto an appropriate area of the print medium. The print controller thus coordinates the timing of the signals needed to control the print device such that an output image is printed in the right place on a print medium.
Various features and advantages of the present disclosure will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example only, features of the present disclosure, and wherein:
In the following description, for purposes of explanation, numerous specific details of certain examples are set forth. Reference in the specification to “an example” or similar language means that a particular feature, structure, or characteristic described in connection with the example is included in at least that one example, but not necessarily in other examples.
Certain examples described herein relate to printing systems and methods of printing. In particular, certain examples relate to ink-jet printing systems that move a print medium in relation to one or more ink-jets. The movement may be due to the movement of an ink-jet across the width of the print medium, or in the case of page-wide array printing, the movement of the medium itself through an ink-jet running across the width of the medium. The ink-jet is generated by ejecting ink from one or more print heads of the printing system. The firing of said print heads may be controlled by controlling the ejection of ink from one or more nozzles of the print head. A nozzle may comprise an ink chamber and a piezoelectric element, wherein activation of the piezoelectric element via a firing pulse ejects ink from the chamber and through the nozzle. Nozzles may be arranged according to print dies, e.g. portions of common silicon substrate.
In these cases, the printing system, or in some cases an external control system, generates a firing pulse signal that controls the deposit of ink on print media. The firing pulse signal has a particular timing or frequency. To achieve high print quality and/or minimize any print errors it is desirable that the firing pulse signal is synchronized with the relative movement of a print medium. This may comprise synchronizing the timing of a firing pulse signal with the movement of the print medium in respect of the one or more ink-jets.
In an example printing system, a media transport system (“media transport” for short) may be arranged to transport print media relative to a print head. In a page-wide array printer, one or more print heads may be mounted on a print bar above a media transport path. In these cases the media transport may transport a print medium underneath the print heads. In certain cases, the media transport may comprise a system that moves the one or more print heads in relation to a print medium; in other cases a combination of print head and print media movement may be effected.
In examples, a state of a media transport may be determined using one or more encoders. Depending on the system these may comprise one or more linear and/or rotary encoders. For example, if the media transport comprises one or more rollers, and/or a belt system, a rotary encoder may be coupled to one of the roller or a drive mechanism such as an electric motor. In these cases, the print medium may be carried by the rollers and/or belt under the print heads. In another case, a linear encoder may track the print media as it moves along a linear path. In each case the encoders may generate an encoder signal representative of the media transport state. This encoder signal may be used to synchronize one or more firing pulse signals.
In comparative examples, fluctuations and deviations from normal operating properties, such as roller and/or belt vibrations due to high-speed operation, may lead to fluctuations in the media transport signal. This can be problematic when synchronizing one or more firing pulse signals. In further comparative examples, other fluctuations and deviations such as slippage of a print medium in respect of the media transport and/or media-specific fluctuations such as curling or snagging can cause the firing pulse signal frequency to be out of synch with the encoder signal.
Certain methods and systems described herein seek to minimize the impact of printing errors that arise due to fluctuations and/or deviations from normal operating properties. Certain methods described herein re-synchronize one or more firing pulse signals to the position of print media using a predictive position following method. This helps to overcome the effects of fluctuations and maintain print quality.
In
In certain cases, print control module 150 additionally processes the received encoder signal, prior to synchronizing the firing encoder signal. For example in certain cases the encoder signal may comprise an encoder signal from one or more of a rotary and linear encoder. In these cases the encoder signal may be processed by one or more of the media encoder 140 and the print control module 150 to generate a media encoder signal. The media encoder signal may comprise a processed form of the encoder signal. The processing may remove noise from the encoder signal. The processing may also or alternatively comprise filtering and/or calibrating the encoder signal based on one or more hardware and/or media properties parameters. For example, if the media transport 130 comprises one or more rollers, then processing of encoder signals may incorporate properties such as roller diameter and run-out as well as other media-specific properties. In certain cases, a media encoder signal comprises one or more of a position and a speed of a print medium being transported by the media transport 130.
In
A number of methods are now described. The methods described in herein may be implemented on the systems described in
At block 320 characteristic properties of a reference signal are varied based on the position of the print medium at the reference time. In an example, the reference signal corresponds to a previously-generated firing encoder signal, as such this block may comprise varying one or more characteristics of the previously-generated firing encoder signal. The one or more one or more characteristics may comprise a timing period or signal frequency. Alternatively, the reference signal may be generated independently and received by a system implementing the method of
At block 330 a firing encoder signal is generated for a time relative to, for example after, the reference time based on the varied characteristics of the reference signal. In the case where the reference signal has a time period representing a movement of the print medium of a predetermined distance, generating the firing encoder signal may comprise determining an error between a predicted distance moved by the print medium based on at least the determined position of the print medium at the reference time and the predetermined distance. The error determined can then be used to vary the time period of the reference signal to generate a firing encoder signal.
At block 340 the firing encoder signal generated at block 330 is used to synchronize the firing of print heads with a print medium.
At block 410 a media encoder signal is sampled. In an example sampling may comprise latching a processed encoder signal at an incremental time period, e.g. every 0.4 ms. At block 420 a time difference between the reference time and an end of a first period of the reference signal is determined. At block 430, the time difference calculated at the previous stage is used to predict the position of the print medium at the end of the first period. This prediction is performed based on an initial position and speed at the reference time, for example as determined from the media encoder. In one case the media encoder signal has a value that is representative of a position of the print medium: in this case the speed may be determined by taking the derivative of this signal. At block 440 a position of the media at the end of a second period from the reference signal is predicted. This may be estimated based on the travel distance assumed by Thing encoder signal (e.g. 0.17 mm) and a time difference between the reference time and the subsequent start of the second period (e.g. 0.17*(time_difference/time_period)). At block 450, the travel time for the print medium to move from the first position to the second position can be determined from previously determined values. For example, the difference in the positions determined at blocks 440 and 430 can be determined and divided by the speed at the reference time that was used in block 430. This travel time may then be used to set the time period of the firing encoder signal waveform.
Block 410 of
p1=p(td)=p(tref)+v(tref)×td.
Following this the second position of the print media 590 as predicted by the reference signal 520 can be determined as:
where l is the resolution of the one or more printing heads and pref,1 585 is the position of the print media at td as predicted,by the reference signal. For example, l may equal 150 (e.g. 150 lines per inch); in a metric equivalent 1/l may equal 0.17×10−3. The position pref,1 585 may be determined using the known travel distance in one period (e.g. 0.17 mm) and multiplying it by a proportion of the complete time period taken up by td. The distance to synchronize ds 560 the media according to the distances determined from the media encoder signal and the reference signal can be determined as:
ds=pref,2−p1.
From which a travel time for the print medium to move from the first position to the second position can be determined as:
The travel time determines the required time period of a firing encoder signal, to synchronize with the position of a print media. The methods enclosed above are used to resynchronize the position of the print media with the firing encoder signal and not the velocity of the media.
Certain methods and systems described herein differ from comparative methods that synchronize one or more firing pulse signals based on a velocity of the print media determined from one or more encoder signals. If synchronization is based on the velocity of the print media then this results in the accrual of additional positional error due to the fact that there exists a delay between measuring the velocity of the media and modifying the firing pulse signal in response to that measurement. Consequently, this leads to an additional, undesirable printing error.
Certain methods and systems disclosed herein mitigate the effects of positional errors by modifying the firing pulse signal based on a position follower method as opposed to a velocity follower method.
Certain examples described herein can be used to improve print quality. The solution of correcting firing pulse signals based on the position of a print media, as opposed to the speed of a media provide greater printing robustness. For example in the case of page-wide array printing, the levels of mismatch in a print using the methods disclosed herein are reduced considerably. In those circumstances, increased fluctuations and perturbations due to the printing being in the media axis as opposed to across the width of the page in the scan axis can lead to increased print defects and print medium/nozzle misalignment. The systems disclosed herein can be used to reduce the impact of these fluctuations.
While examples, presented herein are described with, reference to inkjet printing systems, it will be appreciated that the methods and systems may also be, applied to any other kind of print system in which relative motion between heads (or similar) and print media may suffer from print errors caused by a lack of synchronization between a firing pulse signal (or equivalent) and the relative movement of a respective print medium.
Certain methods and systems as described herein may be implemented by a processor that processes program code that is retrieved from a non-transitory storage medium.
Similarly, it should be understood that a controller may in practice be provided by a single chip or integrated circuit or plural chips or integrated circuits, optionally provided as a chipset, an application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), etc. For example, this may apply to all or part of a controller or other printer control circuitry. The chip or chips may comprise circuitry (as well as possibly firmware) for embodying at least a data processor or processors as described above, which are configurable so as to operate in accordance with the described examples. In this regard, the described examples may be implemented at least in part by computer program code stored in (non-transitory) memory and executable by the processor, or by hardware, or by a combination of tangibly stored code and hardware (and tangibly stored firmware).
The preceding description has been presented to illustrate and describe examples of the principles described. This description is not intended to be exhaustive or to limit these principles to any precise form disclosed. Many modifications and variations are possible in light of the above teaching.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2014/061404 | 6/2/2014 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2015/185101 | 12/10/2015 | WO | A |
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