Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J29/00—Details of, or accessories for, typewriters or selective printing mechanisms not otherwise provided for
  • B41J29/38—Drives, motors, controls or automatic cut-off devices for the entire printing mechanism
  • B41J29/393—Devices for controlling or analysing the entire machine ; Controlling or analysing mechanical parameters involving printing of test patterns
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/015—Ink jet characterised by the jet generation process
  • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
  • B41J2/045—Ink jet characterised by the jet generation process generating single droplets or particles on demand by pressure, e.g. electromechanical transducers
  • B41J2/04501—Control methods or devices therefor, e.g. driver circuits, control circuits
  • B41J2/0451—Control methods or devices therefor, e.g. driver circuits, control circuits for detecting failure, e.g. clogging, malfunctioning actuator
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/015—Ink jet characterised by the jet generation process
  • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
  • B41J2/045—Ink jet characterised by the jet generation process generating single droplets or particles on demand by pressure, e.g. electromechanical transducers
  • B41J2/04501—Control methods or devices therefor, e.g. driver circuits, control circuits
  • B41J2/04573—Timing; Delays
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/015—Ink jet characterised by the jet generation process
  • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
  • B41J2/045—Ink jet characterised by the jet generation process generating single droplets or particles on demand by pressure, e.g. electromechanical transducers
  • B41J2/04501—Control methods or devices therefor, e.g. driver circuits, control circuits
  • B41J2/0458—Control methods or devices therefor, e.g. driver circuits, control circuits controlling heads based on heating elements forming bubbles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/015—Ink jet characterised by the jet generation process
  • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
  • B41J2/045—Ink jet characterised by the jet generation process generating single droplets or particles on demand by pressure, e.g. electromechanical transducers
  • B41J2/04501—Control methods or devices therefor, e.g. driver circuits, control circuits
  • B41J2/04581—Control methods or devices therefor, e.g. driver circuits, control circuits controlling heads based on piezoelectric elements
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/135—Nozzles
  • B41J2/165—Prevention or detection of nozzle clogging, e.g. cleaning, capping or moistening for nozzles

Definitions

• the present invention relates to a solution for increasing the reliability of ink jet printing processes and apparatus. More specifically the invention is related to a method for driving an ink jet print head and an ink jet printing apparatus embodying the method.
• Ink jet printing has become an established technology for conveying information generated by computing devices to the general public.
• DOD drop on demand
• thermal DOD ink jet and piezo DOD ink jet. The difference between both technologies is related to the actuating means driving the drop ejection process, i.e. the way the ejection of a drop is initiated.
• a heater element within the ink chamber causes rapid thermal expansion of a small volume of ink within an ink chamber thereby creating a pressure pulse in the ink that causes a drop of ink to be squeezed out through a nozzle at an end of the ink chamber.
• piezo DOD ink jet piezoelectric material is used to construct part of the ink chamber walls. The piezoelectric material may cause rapid changes of the ink chamber volume, thereby creating a pressure pulse in the ink contained in the ink chamber and squeezing a drop of ink through a nozzle at an end of the ink chamber.
• a first phenomenon is nozzle blockage, caused by deposits of external dust (e.g. paper dust) or precipitation of ink particles (e.g. pigments) in the nozzle.
• Another problem may be causes by long periods of inactivity, leading to changes in the physico-chemical characteristics of the ink located in the nozzle and therefore also leading to a shift of the optimal operating conditions for the drop ejection process. This problem is often referred to as latency.
• Still another problem for the drop ejection process is heat dissipation by the thermal heating elements or the piezoelectric material into the ink contained in the ink chamber. Because the amount of heat dissipated varies with the printing activity, it contributes adversely to a well-defined and reliable operating window for the drop ejection process.
• a third phenomenon is the growth of gas bubbles in the ink chamber as a result of rectified mass diffusion caused by the large acoustic pressure field during the drop ejection process.
• Gas bubbles or seeds may be introduced in the ink chamber through an uncontrolled breakage of the meniscus during drop ejection or because of an improper dissolved gas level concentration of the ink resident in the ink chamber. Gas bubbles reduce the effectiveness of the actuating means in creating the pressure waves driving the drop ejection process. Gas bubbles absorb the acoustic energy. They often inhibit the ejection of drops from the nozzle.
• these latency signals are applied to the printing element actuators during a preset period of time before or after a printing operation, i.e. in non-printing time.
• a latency signal may be applied during the printing operation and replaces the drive signal corresponding with 'no drop ejection' at the specific pixel location.
• a problem of gas bubbles in the ink chamber is in the prior frequently tackled with an active restoration operation, often referred to as a purging operation, wherein the ink chamber is purged (flushed) with ink, with the purpose to drain the gas bubble together with the ink.
• Patent US 5 628 574 to Crowley discloses a web error recovery divert system, wherein a web is printed and scanned for errors. An error is identified in a grouping of sections or pages. A replacement grouping of sections or pages is printed, that is to replace the erroneous grouping. The replacement grouping includes an identifying mark or banner page indicating the presence of a replacement section. The web is redirected through a cutter and diverter that identifies the banner page and, at the appropriate locations, cuts and removes the grouping having the error. The replacement grouping and the remainder of the web is driven to a post-processing unit for further operations. The web error recovery divert system assumes self-recovery of the printer from its erroneous operation in that the system automatically inserts the printing of a replacement grouping of sections or pages, without dedicated actions to restore the erroneous operation of the printer.
• a method and apparatus according to the invention overcome a number of the disadvantages of the prior art in that they provide self-restoration of disturbed print elements while the printing with the inkjet printing system is continued.
• the method detects a disturbance of a printing element (either manually or automatically) and, upon detection, stops driving the actuating means of the printing element for a predetermined period of time, while continuing the consumption of print data for the printing element.
• a series of drops is ejected from a printing element and deposited onto the receiving medium as a pattern of dots.
• the deposited pattern is (at least partly) defined by the relative movement between the receiving medium and the printing element.
• the drop ejection process in the printing element is synchronized with the relative movement of the receiving medium versus the printing element (or vice versa) such that the dots are printed at predefined locations on the receiving medium i.e. a print raster.
• a print raster is used in the digital represent of an image.
• a print raster typically is a two-dimensional grid of individual points, referred to as pixels.
• single pass ink jet printers that are characterized by having a fixed print head and a transport system that moves a receiving medium passed the print head while the print head is printing
• the relative movement of the receiving medium versus the print head results in the printing of dots in a first direction on the receiving medium (further referred to as the scan direction) and the multiple printing elements of the print head, often arranged in a linear array, simultaneously print dots in a second direction (further referred to as the print direction).
• a series of printed dots along the print direction is referred to as a print line and a series of dots along the scan direction is referred to as a scan line.
• Swath ink jet printers are characterized by having a limited width print head and require additional stepping of the print head relative to the receiving medium (or vice versa) in the print direction to cover the full print width.
• a print head moves in a scan direction back and forth across a receiving medium while printing a swath of the digital image and the receiving medium moves stepwise between two print head scans along a print direction perpendicular to the scan direction. Successively printed swaths overlap or adjoin each other in the print direction to create a contiguous image.
• piezo DOD ink jet print head Although the invention is also applicable to thermal and other types of drop on demand ink jet print heads.
• the drop ejection process in ink jet print heads is controlled in the nozzle of a printing element.
• the ink surface tension at the nozzle meniscus must be overcome and the ink volume in the nozzle is accelerated to provide enough kinetic energy to the ink drop ejected from the nozzle.
• the energy to eject a drop of ink from a nozzle is provided through piezoelectric actuators.
• These piezoelectric actuators are designed to quickly change the volume of the ink chamber by deformation of a wall (or part of a wall) of the ink chamber.
• the sudden volume changes impose pressure waves on the ink contained in the ink chamber, travelling towards the open nozzle of the ink chamber and causing ejection of a volume of ink out of the nozzle. Since the drop ejection process is linked to the action of pressure waves in the ink chamber, air bubbles resident in the ink chamber can be real show stoppers for the drop ejection process because they absorb the pressure and damp the pressure waves imposed by the actuators, thereby leaving insufficient energy to eject a drop of ink through the nozzle.
• Air bubbles may find their way into the ink chamber as a result of an uncontrolled drop ejection process, e.g. uncontrolled meniscus breakage and restoration due to accidental particles in or near the nozzle. Air bubbles may also get entrapped as a result of insufficient degassing of the ink supplied to the ink chamber or the phenomenon of bubble growth by rectified diffusion. They may also get entrapped during accidental mechanical impact on the print head, e.g. impact with the receiving medium during medium transport.
• the failing rate decreased to 0.28 failing nozzle per liter ink jetted when inactivity periods of 0.5 s were inserted every 19.85 s.
• the failing further decreased to 0.21 failing nozzle per liter ink jetted when inactivity periods of 0.125 s were used every 2.1 s.
• print heads in swath printers may be regularly brought in an idle state without interrupting the normal printing operation or reducing print production throughput.
• a printing operation in single pass printers may be regarded as a single scan of a page wide print head across the receiving medium. In practice it is often the receiving medium that does the single scan passed a fixed page wide print head. The print head is continuously printing, ejecting drops in synchronism with the transport velocity of the receiving medium, during the whole of the printing operation.
• a solution for realizing periods of inactivity for print heads or printing elements in a single pass printer configuration, without interrupting the printing operation, is provided by analyzing the print data and searching for blanks in the print data during which no drops are to be ejected from the print head or printing element.
• This solution will be first described with a focus on a single printing element and will later on be broadened to cover a solution for a complete multi-color printing apparatus. It will be clear from the description hereinafter that, although the solution solves a specific problem of single pass printers, the solution is not limited thereto and is also applicable to swath printers.
• Print data for a digital printing press may be delivered by a printstreamer or press server to the printing press at the printing press's nominal printing speed.
• the printing press passes the print data on to a print head controller driving the print head.
• Print data is often structured per print line, the print data for each print line comprising a series of pixel values, one pixel value for each pixel location of the print line to be printed with the printing elements of the print head.
• the print head controller translates the print data into driving signals (also referred to as waveforms) for the printing element actuators, e.g. a piezoelectric element.
• the print data may comprise binary pixel values for actuating binary print heads or grayscale pixel values for actuating grayscale print heads.
• the print head controller also receives a print timing signal.
• the print timing signal is provided in synchronism with the receiving medium transport. It triggers the driving signals for the printing element actuators and therefore controls the timing of the drop ejection process defining the moment a binary or grayscale drop is ejected or 'fired' from the printing element, such that the ejected drop is received on the receiving medium on its targeted pixel location.
• the print head controller receives the print data, it examines each pixel value for each individual pixel location and checks whether a drop is to be ejected from a printing element at that pixel location.
• the print data for a printing element comprises a series of consecutive zero pixels, it corresponds to a part in the image where the printing element is not supposed to print ink drops, i.e. a gap in the scan line.
• a gap in a scan line provides an opportunity to install a period of inactivity for the corresponding printing element.
• a period of inactivity for a printing element may be realized by disabling the print timing signal for the printing element, thereby preventing any drive signal from driving the printing element's actuator. It may also be realized by driving the actuator with a 'inactive signal' that is designed to minimize or disable energy input into the printing element.
• the first method may be required if the print head controller, by default, always inserts a latency signal when no drop is to be ejected from the printing element.
• Such a feature may be embedded in the print head controller firmware to prevent latency problems.
• periods of inactivity are chosen to be minimum about 0.3 s. Depending on the print timing signal frequency and the receiving medium transport velocity, this may already be feasible with gaps in the printed image of a few centimeters. Besides gaps in the printed image, also other events may provide an opportunity to install a period of inactivity or an idle time for a printing element.
• These events may be blanks between successive pages in a print job, a receiving medium standstill (e.g. web standstill or exchange of receiver roles), the preparation time for a print job, etc.
• idle periods may be installed without giving in print production time, which is an advantage compared to idle periods installed after detection of a disturbance in the printing element's operation and interruption of the printing operation as disclosed in the prior art.
• Latency is the deterioration of ink in the ink chamber and in the nozzle area over time, with a potential negative impact on ink ejection or jetting reliability. Latency is very much depending on the ink composition and the printing environment, e.g. UV curable inks seem to be less susceptible to latency problems than water based inks.
• a latency signal furhter referred to as a precursor signal
• furhter is designed to stir the ink in the ink chamber and create a short wobble of the meniscus without ejecting a drop from the printing element. It prevents settling of the ink in the ink chamber, local viscosity increases of the ink in the nozzle (as a result of evaporating of ink compounds), and other physicochemical processes that reduce the fit-to-fire condition of the ink.
• Different types of precursor signals have been disclosed in the prior art.
• a suitable precursor signal can readily be selected from the prior art.
• the frequency of application of a precursor signal during a period of inactivity of a printing element is a tradeoff between, on the one hand, avoiding energy input to the printing element to benefit maximally from the inactivity of the printing element and, on the other hand, applying enough stirring of the ink to keep the ink in a fit-to-fire condition.
• a frequency choice may also depend on the ink type used (e.g.
• a precursor signal is preferably applied at a frequency of about 100 Hz.
• a solution for applying a precursor signal to a printing element during a period of inactivity may be to replace the 'inactive signal' with a 'precursor signal' for one or a number of consecutive zero pixels for the printing element, or enable the print timing signal for the printing element for one or a number of consecutive zero pixels and have the embedded precursor signal in the print head controller drive the printing element actuator.
• ink jet print heads may comprise multiple printing elements arranged in one or more arrays, printing element actuators or drive parameters may be individually controllable or en bloc for the entire print head, multiple ink jet print heads may abut each other to create a single page wide print head configuration having a contiguous array of printing elements across the full width of a page, etc.
• print data e.g. a continuous tone (contone) and single color image, e.g. a black & white photograph.
• This image is made available in digital format for preparing the image for printing during a number of prepress steps (e.g. color management, rendering, etc.).
• the digital representation of the image typically comprises a number of image pixels (e.g. 1024 x 768 pixels), each image pixel having a gray value (e.g. 0 to 255).
• gray value e.g. 0 to 255
• Ink jet print heads and printing devices typically have a number of limitations to print the digital representation of an image, e.g. the printing device may have a limited print resolution or the print head may have limited gray scale capability. Therefore a digital image is additionally processed before printing to map the digital representation to the capability of the printing device. This digital image processing is typically executed on a front end system.
• the preprocessed pixel data needs to be allocated to a print head and to printing elements within the print head for actually printing the pixel data on the receiving medium. It is not always possible to decide in advance which of the pixel data will be printed by a given printing element. This decision may for example depend on the specific print head configuration of the printing device, on the composition of multiple images in a single print job or the imposition of multiple print jobs on a single printing device, on dedicated shingling techniques used in swath printers to reduce the visibility of a number of print artefact, etc. It may therefore be preferable to analyze the print data at the print head controller level instead of analyzing image date at the front end system, that is after allocation of print data to printing elements.
• each monochrome image layer is printed with dedicated pint head or print head setup allocated for printing the color of that specific monochrome image layer.
• periods of inactivity have been created to prevent the creation and retention of air bubbles in the ink chamber that may disturb the drop ejection process of the printing element. It has been described that periods of inactivity may be inserted without interrupting the printing process. Therefore the print data is analyzed and 'zero pixels' or sequences of 'zero pixels' in the print data for a given printing element are detected. The printing of 'zero pixels' may then be replaced with periods of inactivity of the printing element. Periods of inactivity may be interrupted with regular precursor signals to preserve a fit-to-fire condition of the ink in the ink chamber and in the nozzle.
• a period of inactivity for a printing element may also be used as a solution to restore a disturbance or a failure in the ejection process of a printing element, as disclosed in US 6 435 672 to Gröninger et al.
• a state of disturbed operation or failure can be detected visually (either manually or with a visual inspection system) or via piezoelectric sensing methods disclosed in that same document.
• the '672 patent further suggests to interrupt the printing, after detection of a disturbance, and resume the printing after a period of inactivity of the printing element(s) has elapsed.
• the stream of print data for the printing elements restoring from a disturbance continues to be consumed from the print server, although the output of the printing elements that are supposed to print this data is suppressed during their restoration.
• This approach has a major advantage towards print job management, especially for single pass printing devices, in that for example the synchronization/registration of the web (receiving medium) transport of the printing operation of the print engine is preserved. Interrupting the printing, as suggested in the prior art, breaks the synchronization between these two processes and it is known that loss of registration of printed images on a receiving medium may be a problem for post-processing equipment of the printed job, such as cutting and folding of the printed material.

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Citations (5)

• 2005
  • 2005-12-07 EP EP05111761A patent/EP1795357A1/de not_active Withdrawn
• 2006
  • 2006-11-30 WO PCT/EP2006/069138 patent/WO2007063101A1/en active Application Filing

Patent Citations (5)

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