Patent Publication Number: US-9844935-B2

Title: Warming printheads during print passes

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application is a continuation of U.S. application Ser. No. 14/787,467, filed Oct. 27, 2015, which is a U.S. National Stage Application of and claims priority to International Patent Application No. PCT/US2013/052028, filed on Jul. 25, 2013, and entitled “WARMING PRINTHEADS DURING PRINT PASSES,” which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Inkjet printing allows recording images on substrates. Inkjet printing may allow for low printer noise, high-speed recording, multi-color recording, and low prices to consumers. Examples of inkjet printers include thermal inkjet printers and piezo inkjet printers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some examples are described with respect to the following figures: 
         FIG. 1  is a flow diagram illustrating a method of reducing decap of printing fluid according to some examples; 
         FIG. 2  is a simplified illustration of a printing system according to some examples; 
         FIG. 3  is a flow diagram illustrating a method of reducing decap of printing fluid according to some examples; 
         FIG. 4  is a chart illustrating temperature profiles of a printpass according to some examples; and 
         FIG. 5  is a substrate for printing according to some examples. 
     
    
    
     DETAILED DESCRIPTION 
     Before particular examples of the present disclosure are disclosed and described, it is to be understood that this disclosure is not limited to the particular examples disclosed herein as such may vary to some degree. It is also to be understood that the terminology used herein is used for the purpose of describing particular examples only and is not intended to be limiting, as the scope of the present disclosure will be defined only by the appended claims and equivalents thereof. 
     Notwithstanding the foregoing, the following terminology is understood to mean the following when recited by the specification or the claims. The singular forms ‘a,’ ‘an,’ and ‘the’ are intended to mean ‘one or more.’ For example, ‘a part’ includes reference to one or more of such a ‘part.’ Further, the terms ‘including’ and ‘having’ are intended to have the same meaning as the term ‘comprising’ has in patent law. 
     Some printing fluids, such as water-based pigmented inks, may be affected by a phenomenon known as ‘decap’, which when recited by the specification or the claims is understood to mean the inability of printing fluid to remain fluid upon exposure to air, thereby potentially leading to degradation of print quality. For example, printing fluid, such as ink, may crust on nozzles of a printhead during periods of a print pass in which the ink is not being ejected by the nozzles. ‘Decap time’ when recited by the specification or the claims is understood to mean the time period in which the printing fluid&#39;s viscosity at a nozzle increases to a threshold sufficient to cause the ejection to fail and cause the nozzle to clog. 
     Accordingly, the present disclosure concerns printing systems, printers, printheads, computer readable storage media, and methods of reducing decap of the printing fluid by warming a printhead and thus its printing fluid during a print pass. By warming the printhead during the print pass based on target temperatures that may be predictively provided before printing the print pass, the decap time of the printing fluid may be increased, and thus decap of the printing fluid may be reduced and/or prevented in any print mode. For example, the decap time may be increased sufficiently that the decap time may be greater than a time elapsed between ejections of printing fluid by a nozzle, thereby reducing and/or preventing decap. Additionally, decap may be preemptively reduced and/or prevented during the early portions of the print pass by warming the printhead to the predictively provided target temperatures during the early portions, in which initial droplets of printing fluid may be ejected. 
     Reduction and/or prevention of decap may be accomplished without causing image quality defects on a plot, without reducing print area on the substrate, without adding any additional work for a user such as cutting the substrate, and without requiring extra servicing such as additional cost per copy or printer cost due to extra hardware such as an extra spittoon. Moreover, the warming may only need to be used as needed to reduce decap, thus printhead life may not be compromised. 
       FIG. 1  is a flow diagram illustrating a method  100  according to some examples. The method  100  may begin at block  102 . At block  102 , at least one drive signal may be determined to drive a printhead to each of a series of target temperatures during respective portions of a print pass by the printhead. Each of the target temperatures may be the greater of a temperature of the printhead caused by printing a quantity of printing fluid to be printed during the respective portion and a predetermined threshold temperature. The method  100  may proceed from block  102  to block  104 . At block  104 , at least one drive signal may be provided to warm the printhead to the series of target temperatures during the respective portions of the print pass. The method  100  may conclude at block  104 . 
       FIG. 2  is a simplified illustration of a printing system  200  according to some examples. The printing system  200  may be or include a printer such as an inkjet printer. In other examples, some of the elements of the printing system  200  may include elements of a printer in addition to elements external to the printer. The printing system  200  may include one or multiple printheads  202 , a media advance mechanism  208 , and a printer controller  210 . The printhead  202  may be used for printing on a substrate  204 . The substrate  204  may be a sheet of substrate  204 , or may be a web, or roll, of substrate  204 . The substrate  204  may be advanced, e.g. longitudinally advanced, through a print zone  205  by a media advance mechanism  208  to complete a print pass  206  that may include a series of portions  209 . The print pass  206  and its portions  209  may advance in the direction shown by the arrows of  FIG. 2 . In some examples, the media advance mechanism  208  may include one or multiple rollers. In other examples, the media advance mechanism  208  may include a transport belt or other suitable media advance device. A printed swath may be generated in one or in multiple print passes  206  of the printheads  202  across the substrate  204 . 
     The printheads  202  may be one or multiple inkjet printheads. In some examples, the printheads  202  may be thermal inkjet printheads. In other examples, the printheads  202  may be piezo inkjet printheads. Each printhead  202  may include an array of printhead nozzles  203  through which drops of printing fluid may be selectively ejected. In some examples, the nozzles  203  may be arranged and spaced apart as a two-dimensional grid. The arrangement and spacing of the nozzles  203  in the printhead may define a printing resolution of the printing system  200 . In some examples, the nozzles  203  may be arranged to allow the printing system  200  to print at resolutions of up to 600 dots per inch (DPI). In other examples, the nozzles may be arranged to allow the printing system  200  to print at other higher or lower resolutions, such as 300 DPI and 1200 DPI. The resolution of the printing system  200  together with the width of the substrate may be printed on defines the number of pixel locations on a substrate  204  that may be printable across the width of the substrate  204 . 
     The printheads  202  may include an array of heating units  207  such as resistors. Each of the printhead nozzles  203  may located adjacent to a corresponding heating unit  207 . In examples where the printheads  202  are thermal inkjet printheads, the printheads  202  may include chambers, each of which may contain a heating unit  207  and printing fluid, and which may be in fluid communication with a corresponding nozzle  203 . A current pulse may be passed through a heating unit  207  to cause the printing fluid in the chamber to vaporize, causing pressurized ejection of droplets of the printing fluid on the substrate  204 . Each heating unit  207  corresponding to a respective nozzle  203  may serve a dual role in that each heating unit  207  may be used both for heating the printing fluid to print the printing fluid from the corresponding nozzle  203 , and for heating the printhead  202  to reduce and/or prevent decap. In examples where the printheads  204  are piezo inkjet printheads, heating units  207  such as resistors may be included as well. 
     The printhead may include a temperature sensor  211 , such as a thermal sense resistor (TSR). The temperature sensor  211  may provide temperature feedback during each portion  209  of the print pass  206 . The temperature feedback may represent the temperature of the printhead  202  during each portion  209  of the print pass  206 . 
     In some examples, the printheads  202  may be mounted on a carriage that may be movable bi-directionally in an axis perpendicular to the media advance direction  206 . In another example the printheads are configured to span the entire width of the media  204  such that the printheads do not need to scan across the print zone  205 , in a so-called page-wide array configuration. If the printheads  202  are multiple inkjet printheads, each printhead  202  may be to print with a different coloured printing inks. In some examples, there may be four printheads  202  each to print with one of a type of printing fluid, such as a cyan (C), magenta (M), yellow (Y), or black (K) color ink. In other examples, there may be a single printhead  202  to print each of a type of printing fluid, such as a cyan (C), magenta (M), yellow (Y), or black (K) color ink, such that each nozzle  203  may be dedicated to printing a one of the types of printing fluid. Printing fluid may be supplied to each printhead  202  by a suitable ink supply system. 
     The operations and methods disclosed herein of the printing system  200  may be implemented and controlled by one or both of a printer controller  210  or by firmware of the printing system  200 . In other examples, the operations and methods disclosed herein of the printing system  200  may be implemented by a graphical image editing computer application, a raster image processor (RIP) application, and/or a printer driver, each of which may be running on a computer, laptop, server, or the like. In some examples, the controller  210  may be a hardware component. For example, the controller  210  may be or may include an application-specific integrated circuit (ASIC) or other hardware component. The controller  210  may be a component of a printer or be located external to the printer. The controller  210  may include a processor  212  such as a microprocessor, a microcontroller, a computer processor, or the like. The processor  210  may, for example, include multiple cores on a chip, multiple cores across multiple chips, multiple cores across multiple devices, or combinations thereof. In some examples, the processor  210  may include at least one integrated circuit (IC), other control logic, other electronic circuits, or combinations thereof. 
     The processor  212  may be in communication with a computer-readable medium  216  via a communication bus  214 . The computer-readable medium  216  may include a single medium or multiple media. For example, the computer readable medium may include one or both of a memory of the ASIC, and a separate memory that stores firmware of the printing system  200 . The computer readable medium  216  may be any electronic, magnetic, optical, or other physical storage device. For example, the computer-readable storage medium  216  may be, for example, Random Access Memory (RAM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), a storage drive, a CD, a DVD, and the like. The computer-readable medium  216  may be non-transitory. The computer-readable medium  216  may store, encode, or carry computer executable instructions  218  that, when executed by the controller  210 , processor  212  or a suitable processing system, may cause the controller  210 , processor  212 , or the suitable processing system to perform any one or more of the methods or operations disclosed herein according to various examples. 
     For example, the computer executable instructions  218  may include instructions for determining a drive signal to drive a printhead  202  to each of a series of target temperatures during respective portions  209  of a print pass  206  by the printhead  202 . Each of the target temperatures may be the greater of a temperature of the printhead  202  caused by printing a quantity of printing fluid to be printed during the respective portion  209  and a predetermined threshold temperature. The drive signal may be based on a plurality of heating quantities that are determined before printing the print pass  206 . The computer-executable instructions  218  may also include instructions for providing the drive signal to warm the printhead  202  to the series of target temperatures while the printhead  202  prints the respective quantities of the printing fluid during the respective portions  209 . 
     Thus, the printing system  200  may comprise a printhead  202  including a plurality of heating units  207  to warm the printhead  202  to a series of target temperatures while the printhead  202  prints respective quantities of the printing fluid during respective portions  206  of a print pass  209 . The printing system  200  may comprise a controller  210  to determine a drive signal to drive the printhead  202  to the series of target temperatures. Each of the target temperatures may be the greater of a temperature of the printhead  202  caused by printing the quantity to be printed during the respective portion  209  and a predetermined threshold temperature. A first target temperature of the series of target temperatures may be greater than the threshold temperature, and a second target temperature of the series of target temperatures may be equal to the threshold temperature. 
       FIG. 3  is a flow diagram illustrating a method  300  of reducing decap of printing fluid according to some examples. In describing  FIG. 3 , reference to  FIGS. 2, 4 and 5  will be made. The ordering of the steps presented herein is in accordance with only some examples of the method  300 . The ordering may be varied, such that some steps may occur simultaneously, some steps may be omitted, and further steps may be added. 
     The method  300  may begin at block  302 . One or more of blocks  302 ,  304 ,  306 , and  308  may be implemented before printing the one or multiple print passes  206 . Thus, blocks  302 ,  304 ,  306 , and  308  may be implemented before a user prints an image on a substrate  204 . 
     At block  302 , a plurality of quantities of printing fluid to be printed during respective portions  209  of one or multiple print passes  206  and/or one or multiple print swaths may be provided and/or determined. In some examples, each of the quantities may represent densities of the printing fluid to be printed on an area of the substrate  204  during the respective portion  209 . In other examples, each of the quantities may represent absolute amounts of the printing fluid to be printed on an area of the substrate  204  during the respective portion  209 . However, in other examples, the quantities may represent values other than densities or absolute amounts of printing fluid. 
     The method  300  may proceed from block  302  to block  304 . At block  304 , one or multiple types of printing fluid to be printed by the printhead  202  during the portions  209  may be provided and/or determined. In some examples, each of the types may represent colors of the printing fluid, such as cyan (C), magenta (M), yellow (Y), or black (K) ink, to be printed on an area of the substrate  204  during the one or multiple print passes  206 . However, in other examples, the types of the printing fluid may represent properties other than colors of the printing fluid. In some examples, the printhead  202  may print with a single color printing fluid during the print passes  206 . In other examples, the printhead  202  may print each color of printing fluid, for example cyan (C), magenta (M), yellow (Y), or black (K) ink. 
     Taken together, the plurality of quantities and/or types of blocks  302  and  304  may represent an image to be printed by the printhead  202 . Thus, an image to be printed by the printhead  202  may be provided and/or determined. The determined quantities and types may be stored in the computer readable medium  216  as image data, such as a printhead control data. 
       FIG. 4  is a chart  220  illustrating an inherent temperature profile  222  and an adjusted temperature profile  224 , each of which may be relationships between temperature  221  shown on the y-axis and a location of the print pass  206  on the x-axis. 
       FIG. 5  illustrates a substrate  204  for printing which may include regions  234  in which a low quantity of printing fluid may be printed, and regions  236  in which a high quantity of printing fluid may be printed. Each of the regions  234  and  236  may correspond to a portion  209  of the print pass  206 , as shown. 
     The method  300  may proceed from block  304  to block  306 . At block  306 , heating quantities may be provided and/or determined. In some examples, the heating quantities may represent a series of temperatures of the printhead  202  caused by printing the determined respective quantities and/or types of printing fluid during the respective portions  209 . In other examples, each of the heating quantities may represent respective voltages, currents, energies, or other quantities that may be applied to heating units  207  to achieve the series of temperatures that may be caused by printing the determined respective quantities. The voltages, currents, energies, or other quantities that may achieve the series of temperatures may depend on physical characteristics of the printhead  202 . 
     Thus, the determination of the heating quantities may be made based on the determined quantities of printing fluid and/or types of printing fluid. The series of temperatures, taken together, may define an inherent temperature profile  222  of the one or multiple print passes  206 . A lower temperature  232  may result in printing the regions  234  having a lower quantity of printing fluid during a portion  209 , because lower energy of the current pulses generated by the heating units  207  may cause droplets of ejected printing fluid to be smaller in volume. A higher temperature  228  may result in printing the regions  236  having a higher quantity of printing fluid during a portion  209 , because higher energy of the current pulses generated by the heating units  207  may cause droplets of ejected printing fluid to be larger in volume. 
     In some examples, the heating quantities may be predetermined. For example, in prior testing of the printhead  202 , the temperature sensor  211  may have provided temperature feedback representing a series of temperatures of the printhead  202  caused by printing any given series of quantities and types of printing fluid during each portion  209 . The heating quantities, which may represent the temperatures, voltages, currents, or energies, may be stored in the computer-readable medium  216  in lookup tables that may map each heating quantity such as a temperature to a quantity of printing fluid and/or to a type of printing fluid. Some examples, the lookup tables may map each heating quantity to each of the combinations of a quantity of inkjet and a type of printing fluid that would generate that temperature. 
     In some examples, each of the heating quantities may be determined by the controller  210  based on the determined respective quantities and/or types of printing fluid, for example by using data stored in the computer-readable medium  216  such as mathematical formulas which may represent how to convert the determined respective quantities and/or types of printing fluid into the heating quantities. 
     In some examples, a particular temperature of the temperature profile  222  may depend only on the quantity and/or type of printing fluid to be printed during the respective portion  209 . In other examples, a particular temperature of the temperature profile  222  may depend both on the quantity and/or type of printing fluid to be printed during the respective portion  209  as well as on the quantities and/or type of printing fluid to be printed in other portions  209 , such as a portion  209  immediately previous to the portion  209  for which the particular temperature may be determined and/or stored. For example, the heating of the printhead  202  due to printing the immediately previous quantity and/or type of printing fluid may partially carry over to the temperature of the printhead  202  during the printing of the current quantity and type of printing fluid. 
     The method  300  may proceed from block  306  to block  308 . At block  308 , a threshold heating quantity such as a threshold temperature  230  may be provided. The threshold heating quantity may be predetermined and/or stored by the controller  210 . The threshold temperature  230  may be a temperature sufficiently high to reduce decap and/or prevent decap of the printing fluid. The threshold temperature  230  may be below a temperature at which overheating of the printhead  202  may occur. In other examples, the threshold heating quantity may be threshold voltages, threshold currents, or threshold energies that may be applied to the heating units  207  that may be sufficiently high to reduce decap and/or prevent decap of the printing fluid. 
     The method  300  may proceed from block  308  to block  310 . At block  310 , in response to one or more of the heating quantities such as the temperatures provided at block  306  being below the threshold heating quantity such as the threshold temperature  230 , the one or more of the heating quantities such as the temperatures may be adjusted to the threshold heating quantity such as the threshold temperature by adding an additionally heating quantity such as an additional temperature  226 , as shown in  FIG. 4 . Thus, each of the temperatures in the adjusted temperature profile  224  may be equal to or above the threshold temperature  230 . The adjustment may increase one or multiple temperatures by, for example, between about 5 and about 20 degrees Celsius, or by about 50%. 
     In some examples, the heating quantities such as temperatures that may have been adjusted to the heating quantity threshold such as the threshold temperature may be changed in the lookup table. In other examples, a second lookup table may be provided which contains the non-adjusted heating quantities such as the non-adjusted temperatures as well as the adjusted heating quantities such as the adjusted temperatures. The temperatures in the first modified table or the second table may be referred to as target heating quantities such as target temperatures, as these target temperatures may later be used to heat the printhead  202  while printing the respective portions  209 . 
     When printing a region  234  having a low quantity of printing fluid in a portion  209 , the ink ejection may generate low energy and a low temperature  232 , which may result in decap of the printing fluid. In that case, the adjustment of the low temperature  232  to the threshold temperature  230  may reduce and/or prevent decap. When printing high quantities of printing fluid a portion  209 , the ink ejection may generate high energy and a high temperature  228 , which may result in low decap or no decap. In that case, no adjustment of the high temperature may be implemented. Because too much additional temperature  226  may compromise the life of the printhead  202 , and because the additional temperature  226  of the adjustment may be implemented only if a temperature may be below the threshold temperature  230  and not when the adjustment is not needed in regions  236  having high quantities of printing fluid, the life of the printhead  202  may be optimized. 
     Thus, at blocks  306  and  308 , each of the target heating quantities such as target temperatures may be selected from between a greater of (1) the heating quantities such as the temperature of the printhead  202  caused by printing the quantity and/or type of printing fluid to be printed during the respective portion  209  of the one or multiple print passes  206  and (2) the predetermined threshold heating quantity such as the predetermined threshold temperature  230 . 
     At least a first determined heating quantity or a first plurality of determined heating quantities may be greater than a threshold heating quantity, and at least a second determined heating quantity or a second plurality of determined heating quantities may be equal to the threshold heating quantity. For example, at least a first determined target temperature or a first plurality of determined target temperatures may be greater than the threshold temperature  230 , and at least a second determined target temperature or a second plurality of determined target temperatures may be equal to the threshold temperature  230 . 
     The method  300  may proceed from block  310  to blocks  312  and  314 . Blocks  312  and  314  may be implemented during the printing the one or multiple print passes  206  as a closed-loop algorithm such as a proportional-integral-derivative (PID) algorithm. 
     At block  312 , the temperature sensor  211  may continuously provide, during each portion  209 , temperature feedback that may represent the temperature of the printhead  202  during each portion  209 . 
     The method  300  may proceed from block  312  to block  314 . At block  314 , a drive signal may be determined and provided by the printer controller  210  to drive the printhead  202  to warm, by the heating units  207 , the printhead  202  and thus the printing fluid of the printhead  202  to the series of target temperatures during the respective portions  209 . The warming may serve dual purposes. 
     First, the warming may cause the printhead  202 , under control of the printer controller  210 , to eject drops of printing fluid onto substrate pixel locations on the substrate  204  positioned in the print zone  205  to print the image. During each portion  209 , the printhead  202  may print the respective quantity and type of printing fluid by ejecting the printing fluid from suitable nozzles  203  to print the inkjet at the appropriate locations and appropriate densities on the substrate  204 . Second, the warming may be used to provide additional heating the printhead  202  to reduce and/or prevent decap without causing undesired ejection of printing fluid. 
     To accomplish the dual purposes of the warming, each nozzle  203  may be utilized with sufficient frequency such that the time between successive current pulses passed through the nozzle  203  by its heating unit  205  to eject the printing fluid may be less than the decap time of the printing fluid being ejected. For example, the usage of the nozzles  203  may be randomized in such a way that does not affect image to be printed, yet that may ensure that each nozzle  203  is utilized with sufficient frequency, as discussed above. Additionally, in some examples, the additional temperature  226  provided at block  310  may be provided by heating the nozzles  203  according to the randomization scheme described above, or by providing uniformly heating all nozzles  203  of the printhead  202  to provide the additional temperature  226 . However, in other examples, nozzles  203  which may not be used during the portion  209  to eject printing fluid may be selectively heated with selective current pulses by their respective heating units  203  to provide the additional temperature  226 . The selective current pulses may have insufficient energy to vaporize the printing fluid and thus may have insufficient energy to cause the unused nozzles  203  to eject the printing fluid. Thus, the additional temperature  226  may be provided without causing undesired ejection of printing fluid. 
     The controller  210  may take into account the temperature feedback obtained at block  312  when providing the drive signal to warm the heating units  207  and thus the printing fluid of the printhead  202 . Thus, the temperature sensor  211  may provide temperature feedback to allow the heating units  207  to warm the printhead  202  based on the temperature feedback, and such that the drive signal may be based on the temperature feedback. 
     For example, in response to the heating units  207  unsuccessfully warming the printhead  202  to a correct target temperature by overshooting or undershooting the target temperature, the controller  210  may adjust, e.g. increase or decrease, the amount of heat provided by the heating units  207  such that the printhead  202  and thus the printing fluid of the printhead  202  are warmed to the correct target temperature. 
     If all print swaths, including all their print passes  206 , are completed, then the method  300  may conclude. If all swaths, including all their print passes  206 , have not completed, then the method  300  may proceed from block  314  to block  312 . 
     Thus, there have been described examples of printing systems, printers, printheads, computer readable storage media, and methods of reducing decap of the printing fluid by warming the printing fluid during a print pass. In the foregoing description, numerous details are set forth to provide an understanding of the subject disclosed herein. However, examples may be practiced without some or all of these details. Other examples may include modifications and variations from the details discussed above. It is intended that the appended claims cover such modifications and variations.