Patent Publication Number: US-2023158794-A1

Title: Liquid discharge apparatus

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Japanese Patent Application No. 2021-190956 filed on Nov. 25, 2021. The entire content of the priority application is incorporated herein by reference. 
    
    
     BACKGROUND ART 
     Conventionally, there is known an ink jet apparatus (liquid discharge apparatus) configured to generate pressure wave inside an ink flow channel by way of applying a drive signal to an actuator to discharge ink from a nozzle. In such an ink jet apparatus, the drive signal has three pulse signals in total consisted of two jet pulse signals and one non-jet pulse signal for a printing command per one dot (within one discharge period). 
     DESCRIPTION 
     In recent years, liquid discharge apparatuses are required for driving the actuator at high frequency from the point of view of high-speed recording. If the frequency of the drive signal is 20 kHz or so, then it is possible to discharge liquid stably from the nozzle according to the drive signal as described above. However, if the frequency of the drive signal is further raised, then the discharges may be unstable with the drive signal as described above. 
     An object of the present disclosure is to provide a liquid discharge apparatus capable of realizing stable discharges under a condition that the actuator is driven at high frequency. 
     According to an aspect of the present disclosure, there is provided a liquid discharge apparatus including: 
     a channel member defining a nozzle and a pressure chamber in communication with the nozzle; 
     an actuator configured to apply pressure to liquid in the pressure chamber; and 
     a controller configured to apply a drive signal to the actuator, 
     wherein the drive signal includes a rectangular main pulse and a rectangular cancel pulse applied after the main pulse within one discharge period for forming one dot, the cancel pulse being smaller in pulse width than the main pulse, 
     the actuator is driven by the drive signal in a pull-and-push method such that the liquid is discharged from the nozzle by increasing volume of the pressure chamber from a predetermined volume and then decreasing the volume of the pressure chamber to the predetermined volume or less, and 
     if f (kHz) refers to a drive frequency of the drive signal, if Tw (μsec) refers to a time length from a falling edge of the main pulse to a rising edge of the cancel pulse, and if Tc (μsec) refers to a pulse width of the cancel pulse, then the following expression holds: 
       50≤f≤−11.3×(Tw+Tc)+120.
 
       FIG.  1    is a schematic plan view of a printer according to an embodiment of the present disclosure. 
       FIG.  2    is a plan view of a head included in the printer. 
       FIG.  3    is a cross section view of the head along the line of  FIG.  2   . 
       FIG.  4    is a block diagram depicting an electric configuration of the printer. 
       FIG.  5    is a graph depicting a drive signal supplied to an actuator by a driver IC of the head. 
       FIG.  6    is a graph depicting a relationship between a limiting frequency and a time related to a cancel pulse included in the drive signal. 
       FIG.  7    is a graph depicting a relationship between the limiting frequency and a total time related to three pulses included in the drive signal. 
       FIG.  8    is a graph depicting a displacement of meniscus along with applying the drive signal. 
       FIG.  9    is a graph depicting a relationship between the limiting frequency, and the product of the maximum displacement of meniscus occurring after applying the cancel pulse, and the time from the start point of applying the drive signal to the point of the maximum displacement occurring. 
    
    
     A printer  1  according to an embodiment of the present disclosure includes, as depicted in  FIG.  1   , a carriage  2  being movable in a scanning direction (a direction orthogonal to a vertical direction) while holding a head  3 , a platen  6  supporting paper P below the head  3  and the carriage  2 , a conveying mechanism  4  conveying the paper P in a conveyance direction (a direction orthogonal to the conveyance direction and the vertical direction), and a controller  100 . A plurality of nozzles  31  are formed in the lower surface of the head  3 . In this embodiment, the resolution of images formed with an ink discharged from the nozzles  31  is 1,200 dpi or more. The plurality of nozzles  31  align in the conveyance direction (the direction of relative displacement between the paper P being a recording medium and the plurality of nozzles  31 ), at a density of 50 dpi or more. 
     The carriage  2  is supported by a pair of guide rails  7  and  8  extending in the scanning direction. When driven by a carriage motor  2 M under the control of the controller  100 , the carriage  2  is moved in the scanning direction along the guide rails  7  and  8 . 
     The conveying mechanism  4  includes two roller pairs  11  and  12  arranged in positions to interpose the platen  6  and the carriage  2  therebetween in the conveyance direction. The roller pairs  11  and  12  are driven by a conveyance motor  4 M (see  FIG.  4   ) under the control of the controller  100  to rotate with the paper P being nipped therebetween. By virtue of this, the paper P is conveyed in the conveyance direction. 
     As depicted in  FIGS.  2  and  3   , the head  3  includes a flow channel member  21 , an actuator member  22  arranged on a surface  21   a  of the flow channel member  21 , and a sealing member  23  arranged between the flow channel member  21  and the actuator member  22 . 
     The flow channel member  21  is constructed from, as depicted in  FIG.  3   , nine plates  41  to  49 . The plates  41  to  49  are stacked on each other in the vertical direction (the thickness direction of each of the plates  41  to  49 ). The plates  41  to  49  are made of a metallic material (stainless steel or the like). 
     A plurality of pressure chambers  30  are formed in the plate  41 . The plurality of nozzles  31  are formed in the plate  49 . The plate  41  has a surface  41   a  which serves as the surface  21   a  of the flow channel member  21 , whereas the plate  49  has a backside surface  49   b  which serves as the backside surface  21   b  of the flow channel member  21 . The plurality of pressure chambers  30  are open at the surface  21   a  whereas the plurality of nozzles  31  are open at the backside surface  21   b.    
     Four common flow channels  29  (see  FIG.  2   ) are formed in the plates  44  to  48 . A communication flow channel  35  is formed in the plates  42  and  43  for communication between each pressure chamber  30  and the corresponding common flow channel  29 . A connection flow channel  36  is formed in the plates  42  to  48  for connection between each pressure chamber  30  and the corresponding nozzle  31 . 
     The four common flow channels  29  extend respectively in the conveyance direction, as depicted in  FIG.  2   , and align in the scanning direction. The common flow channels  29  are provided according to each pressure chamber array formed from the plurality of pressure chambers  30  arrayed in the conveyance direction. From each common flow channel  29 , the ink is supplied to the plurality of pressure chambers  30  belonging to each pressure chamber array via the communication flow channels  35  (see  FIG.  3   ). Then, as will be described later on, each actuator  22   x  of the actuator member  22  undergoes a deformation to apply a pressure to the ink in the pressure chamber  30  such that the ink is discharged from the nozzle  31  through the connection flow channel  36 . 
     In this manner, the flow channel member  21  is formed therein with the four common flow channels  29 , and a plurality of individual flow channels  32  in respective communication with the common flow channels  29  (the plurality of individual flow channels  32  being the flow channels including the pressure chambers  30  and the nozzles  31 , and being the flow channels from the exits of the common flow channels  29  to the nozzles  31  through the communication flow channels  35 , the pressure chambers  30 , and the connection flow channels  36 ). 
     As depicted in  FIG.  2   , two supply ports  27  and two feedback ports  28  are formed in the surface  21   a  of the flow channel member  21 . The two supply ports  27  are arranged on the upstream side of the four common flow channels  29  in the conveyance direction. The two feedback ports  28  are arranged on the downstream side of the four common flow channels  29  in the conveyance direction. The supply ports  27  and the feedback ports  28  are in respective communication with an ink tank  9  (see  FIG.  1   ) via tubes or the like. Each supply port  27  is in communication with two common flow channels  29  adjacent to each other in the scanning direction to supply the ink to the two common flow channels  29  from the ink tank  9 . Each feedback port  28  is in communication with the other two common flow channels  29  adjacent to each other in the scanning direction to feed the ink back to the ink tank  9  from the two common flow channels  29 . 
     The actuator member  22  is arranged centrally on the surface  21   a  of the flow channel member  21  to cover all pressure chambers  30  open at the surface  21   a  but not cover the supply ports  27  and the feedback ports  28 . The actuator member  22  includes, as depicted in  FIG.  3   , two piezoelectric layers  61  and  62 , a common electrode  52 , and a plurality of individual electrodes  51 . The piezoelectric layers  61  and  62  and the common electrode  52  define the contour of the actuator member  22  depicted in  FIG.  2   , which is rectangular and one size smaller than the flow channel member  21  as viewed from the vertical direction. On the other hand, each pressure chamber  30  is provided with an individual electrode  51  which overlaps in the vertical direction with the corresponding pressure chamber  30 . 
     The plurality of individual electrodes  51  and the common electrode  52  are connected electrically with the driver IC  5 D (see  FIG.  4   ). The driver IC  5 D keeps the common electrode  52  at the grounding potential while causing the individual electrodes  51  to change between a predetermined drive potential and the grounding potential. In particular, the driver IC  5 D generates a drive signal on the basis of a control signal from the controller  100 , and supplies the drive signal to the individual electrodes  51 . By virtue of this, the individual electrodes  51  change between the predetermined drive potential and the grounding potential. On this occasion, in the piezoelectric layer  61 , the parts interposed between the individual electrodes  51  and the common electrode  52  (the actuators  22   x ) contract in a planar direction due to a piezoelectric transversal effect. Along with this, in the actuator member  22  and the sealing member  23 , the parts overlapping in the vertical direction with the pressure chambers  30  deform to project toward the pressure chambers  30  such that the pressure chambers  30  decrease in volume and a pressure is applied to the ink in the pressure chambers  30 . Therefore, the ink is discharged from the nozzles  31  through the connection flow channels  36 . At the same time, the ink in the common flow channels  29  is supplied to the pressure chambers  30  through the communication flow channels  35 ; furthermore, from the ink tank  9 , the ink is supplied to the common flow channels  29 . 
     The plurality of actuators  22   x  formed in the actuator member  22  function as unimorph type actuators capable of deformation independently according to the voltage application of the driver IC  5 D to each individual electrode  51 . 
     As depicted in  FIG.  2   , in the same manner as the actuator member  22 , the sealing member  23  is arranged centrally on the surface  21   a  of the flow channel member  21  to cover all pressure chambers  30  open at the surface  21   a  but not cover the supply ports  27  and the feedback ports  28 . The sealing member  23  is rectangular and one size smaller than the flow channel member  21  but one size larger than the actuator member  22  as viewed from the vertical direction. The sealing member  23  is attached on the surface  21   a  with an adhesive to seal up the pressure chambers  30 . The sealing member  23  is made of a different material from the piezoelectric layers  61  and  62  (of a material of low ink permeability such as stainless steel or the like), without the parts functioning as actuators. 
     In this embodiment, each of the piezoelectric layers  61  and  62  is as thick as 10 μm or more, the sealing member  23  is also as thick as 10 μm or more, and each of the electrodes  51  and  52  is as thick as 0.5 to 1.5 μm or more. 
     The controller  100  includes, as depicted in  FIG.  4   , a CPU (Central Processing Unit)  101 , a ROM (Read Only Memory)  102 , and a RAM (Random Access Memory)  103 . The ROM  102  stores programs and data for the CPU  101  to carry out various controls. The RAM  103  temporarily stores data for the CPU  101  to use in executing a program. The CPU  101  carries out the various controls according to the programs and data stored in the ROM  102  and the RAM  103  on the basis of the data inputted from an external device (a personal computer or the like) or from an input unit (switches and/or buttons provided on the outer surface of the casing of the printer  1 ). 
       FIG.  5    depicts an example of the drive signal which is supplied by the driver IC  5 D to the individual electrodes  51  under the control of the controller  100 . The drive signal X depicted in  FIG.  5    includes three pulses in respective rectangular shapes within one discharge period for forming one dot (from the point of time t 0  to the point of time t 1 ). These three pulses are consisted of a main pulse Pm, a prepulse Pp applied before the main pulse Pm, and a cancel pulse Pc applied after the main pulse Pm. The main pulse Pm serves for discharging liquid droplets in a predetermined size from the nozzles  31  within one discharge period. It is preferable for the main pulse Pm to have a pulse width Tm near to AL (Acoustic Length: reciprocating conveyance time for the pressure wave in the individual flow channels  32 ), from the point of view of raising the discharge pressure. The prepulse Pp and the cancel pulse Pc serve for suppressing satellites and mists and have pulse widths Tp and Tc smaller than the pulse width Tm of the main pulse Pm. 
     In this embodiment, in the initial state (at the time t 0 ), the predetermined drive potential (VDD) is applied to the individual electrodes  51 , so that in the piezoelectric layer  61 , the parts interposed between the individual electrodes  51  and the common electrode  52  (the actuators  22   x ) contract in the planar direction. Therefore, in the actuator member  22  and the sealing member  23 , the parts overlapping in the vertical direction with the pressure chambers  30  deform to project toward the pressure chambers  30 . Then, at the timing of the main pulse Pm rising up for the individual electrodes  51  to reach the grounding potential (0V), the actuators  22   x  are released from contracting in the planar direction to let the abovementioned parts become flat. By virtue of this, the pressure chambers  30  each increase in volume to be larger than that in the initial state such that the ink is inhaled into the individual flow channels  32  from the common flow channels  29 . Further, after that, when the main pulse Pm falls down and the drive potential (VDD) is applied to the individual electrodes  51 , the actuators  22   x  contract in the planar direction again such that those parts deform again to project toward the pressure chambers  30 . On this occasion, the pressure on the ink increases due to the decrease of the volume of the pressure chambers  30  such that the ink is discharged from the nozzles  31 . 
     Note that the term “rising edge” of a pulse refers to a potential change from the potential of the initial state to a predetermined potential of that pulse. The term “falling edge” of a pulse refers to a potential change from the predetermined potential to the potential of the initial state of that pulse. In this embodiment, because the “pull-and-push” method is adopted, as depicted in  FIG.  5   , the potential decreases at the rising edge of the pulse whereas the potential increases at the falling edge of the pulse. 
     That is, in this embodiment, as the method for driving the actuators  22   x,  a “pull-and-push” method is adopted to discharge the ink from the nozzles  31  by way of first increasing the volume of the pressure chamber  30  from a predetermined volume and then decreasing the volume to the predetermined volume or less. In the “pull-and-push” method, when the volume of a pressure chamber  30  increases, a negative pressure wave arises in the pressure chamber  30 , and then at the timing when the negative pressure wave is inversed to return to the pressure chamber  30  as a positive pressure wave, the volume of the pressure chamber  30  is reduced such that by giving rise to the positive pressure wave in the pressure chamber  30 , those pressure waves overlap. With the pressure waves overlapping in this manner, a large pressure is applied to the ink in the pressure chamber  30  such that it is possible to raise the discharge pressure. 
     Further, in recent years, from the point of view of high-speed recording, it is required that the actuators  22   x  be driven at high frequency. However, with the drive signal X including the rectangular main pulse Pm and the rectangular cancel pulse Pc within one discharge period as depicted in  FIG.  5   , if the frequency is 50 kHz or higher, then the discharges can be unstable. 
     The present inventors have found, through their devoted research, that the sum of Tw (the time length from a falling edge of the main pulse Pm to a rising edge of the cancel pulse Pc) and Tc (the pulse width of the cancel pulse Pc) correlates with the limiting frequency Fl (the limiting frequency at which successively discharged ink droplets are disconnected and the dots are formed independently according to each ink droplet). 
       FIG.  6    depicts a relationship between Tw+Tc related to the cancel pulse Pc, and the limiting frequency Fl.  FIG.  7    depicts a relationship between the total time Tt (=Tp+Tv+Tm+Tw+Tc) related to the three pulses Pp, Pm, and Pc, and the limiting frequency Fl.  FIGS.  6  and  7    plot the respective values of the limiting frequency Fl when the actuator  22   x  is driven by using a plurality of drive signals X where at least some of the following items are different from each other: Tp (the pulse width of the prepulse Pp), Tv (the time length from the falling edge of the prepulse Pp to the rising edge of the main pulse Pm), Tm (the pulse width of the main pulse Pm), Tw (the time length from the falling edge of the main pulse Pm to the rising edge of the cancel pulse Pc), and Tc (the pulse width of the cancel pulse Pc). Further, in  FIGS.  6  and  7   , while the expression of a regression analysis on the limiting frequency Fl is depicted with a broken line, it is understood that compared to the expression “−10.4×Tt×190” depicted in  FIG.  7   , the expression “−11.3×(Tw+Tc)+120” depicted in  FIG.  6    renders a closer approximation of the actual limiting frequency Fl. 
     Therefore, in this embodiment, let f be the drive frequency (kHz) of the drive signal X, Tw be the time length (μsec) from the falling edge of the main pulse Pm to the rising edge of the cancel pulse Pc, and Tc be the pulse width (μsec) of the cancel pulse Pc. Then, the following expression (1) holds (in other words, in the case of the drive at any frequency f equal to or higher than 50 kHz, Tw+Tc is set to let the following expression (1) hold). By virtue of this, it is possible to realize stable discharges by the drive at high frequency. 
       50≤f≤−11.3×(Tw+Tc)+120   (1)
 
     Further, the present inventors have also paid attention to the displacement of meniscus formed in the nozzles  31 , and found that the limiting frequency Fl correlates with the product of the maximum displacement Q (see  FIG.  8   ) of meniscus occurring after applying the cancel pulse Pc, and the time Tq from the start point t 2  (see  FIG.  5   ) of applying the drive signal X to the point tq of the maximum displacement Q occurring within one discharge period. 
       FIG.  8    depicts the displacement of meniscus along with the application of the drive signal X. In  FIG.  8   , R refers to the maximum displacement of meniscus occurring after applying the main pulse Pm, and tr refers to the point of time when the maximum displacement R occurs.  FIG.  9    depicts a relationship between the limiting frequency Fl and the product of Q and Tq. Like  FIGS.  6  and  7   ,  FIG.  9    plots the respective values of the limiting frequency Fl when a plurality of drive signals X are used where at least some of the following items are different from each other: Tp, Tv, Tm, Tw, and Tc (see  FIG.  5   ). Further, while the expression “−4×10 14 ×(Q×Tq)+106” of a regression analysis on the limiting frequency Fl is depicted with a broken line, it is understood that this expression renders an approximation of the actual limiting frequency Fl. 
     Therefore, in this embodiment, let Q (m 3 ) be the maximum displacement after applying the cancel pulse Pc, and let Tq (μsec) be the time length from the start point t 2  (see  FIG.  5   ) of applying the drive signal X to the point tq of the maximum displacement Q occurring within one discharge period. Then, the following expression (2) holds (in other words, in the case of the drive at any frequency f equal to or higher than 50 kHz, Tq is set to let the following expression (2) hold). By virtue of this, it is possible to realize stable discharge further reliably by the drive at high frequency. 
       f≤−4×10 14 ×(Q×Tq)+106   (2)
 
     In this embodiment, the resolution of images formed with the ink discharged from the nozzles  31  is 1,200 dpi or more. In order to realize a high resolution at 1,200 dpi or more, the drive at high frequency is effective. Hence, letting the above expressions (1) and (2) hold, it is possible to realize stable discharges by the drive at high frequency. 
     The plurality of nozzles  31  align in the conveyance direction (the direction of relative displacement between the paper P being a recording medium and the plurality of nozzles  31 ), at a density of 50 dpi or more. In this case, by providing a plurality of arrays of the nozzles  31  aligning at that density, it is possible to effectively realize a high resolution at 1,200 dpi or more. 
     Further, in this embodiment, let Tm (μsec) be the pulse width of the main pulse Pm and AL (μsec) be the reciprocating conveyance time for the pressure wave in the individual flow channels  32 . Then, the following expression (3) holds (in other words, Tm is set to let the following expression (3) hold). By virtue of this, it is possible to raise the discharge pressure. 
       AL×0.7≤Tm≤AL×1.3   (3)
 
     AL is 6 μsec or less. If AL exceeds 6 μsec, then the pulse width Tm of the main pulse Pm becomes longer (accordingly one discharge period becomes longer) such that it is difficult to realize the drive at high frequency. In this embodiment, because AL is 6 μsec or less, the pulse width Tm of the main pulse Pm is short (accordingly one discharge period is short) such that it is easy to realize the drive at high frequency. 
     Tw is 1 μsec or more and Tc is also 1 μsec or more (see  FIG.  5   ). It takes 1 μsec or so for the pulse to rise up or fall down. Further, there is some difference in time between rising up and falling down for each actuator  22   x.  If Tw or Tc is less than 1 μsec, then some of the plurality of actuators  22   x  may fail to rise up or fall down completely. Therefore, the difference in time between rising up and falling down for each actuator  22   x  may distinctly affect the discharge performance to give rise to variation of the discharge performance between the nozzles  31 . In this embodiment, however, with Tw and Tc being 1 μsec or more, it is possible to prevent this problem. 
     The nozzles  31  are constructed from a metallic member (the plate  49  depicted in  FIG.  3   ). Metals have a better quality of abrasion resistance than resins such as polyimide and the like. Therefore, there is little abrasion of the nozzles  31  even used over a long time, so that it is possible to realize stable discharges by the drive at high frequency. 
     Between the flow channel member  21  and the actuator member  22 , there is arranged the sealing member  23  made of a different material from the piezoelectric layers  61  and  62 . Accordingly, even if a crack emerges in the piezoelectric layers  61  and  62 , the ink in the flow channel member  21  will not come into the crack of the piezoelectric layers  61  and  62  such that it is possible to prevent problems (such as short circuit between the electrodes  51  and  52  due to the ink entering the crack. 
     &lt;Modifications&gt; 
     While the invention has been described in conjunction with various example structures outlined above and illustrated in the figures, various alternatives, modifications, variations, improvements, and/or substantial equivalents, whether known or that may be presently unforeseen, may become apparent to those having at least ordinary skill in the art. Accordingly, the example embodiments of the disclosure, as set forth above, are intended to be illustrative of the invention, and not limiting the invention. Various changes may be made without departing from the spirit and scope of the disclosure. Therefore, the disclosure is intended to embrace all known or later developed alternatives, modifications, variations, improvements, and/or substantial equivalents. Some specific examples of potential alternatives, modifications, or variations in the described invention are provided below. 
     In the above embodiment, the drive signal X (see  FIG.  5   ) includes the prepulse Pp in addition to the main pulse Pm and the cancel pulse Pc within one discharge period (from the time t 0  to the time t 1 ). However, the prepulse Pp may be omitted. 
     In the above embodiment, the actuator is constructed from two layers including the individual electrodes and the common electrode. However, the actuator may be constructed from three layers (such as, for example, a structure including driver electrodes to which a high potential or a low potential is selectively applied, a high potential electrode kept at the high potential, and a low potential electrode kept at the low potential). 
     The head is not limited to a serial type but may be of a line type. 
     The ink discharging object is not limited to paper but may be cloths, substrates, plastic members, and the like. 
     The liquid discharged from the nozzles is not limited to inks but may be any liquids (such as processing liquids agglutinating or depositing ingredients of inks). 
     The present disclosure is not limited to application to printers but can be applied to facsimile devices, photocopy devices, multifunctional devices, and the like. Further, the present disclosure can also be applied to liquid discharge apparatuses used for other purposes than recording images (such as liquid discharge apparatuses of forming electrically conductive patterns by discharging an electrically conductive liquid to a substrate).