JP4238893B2 - Inkjet recording device - Google Patents

Description

  The present invention relates to an ink jet recording apparatus that performs printing by discharging ink droplets.

  An inkjet head included in an inkjet recording apparatus that ejects ink droplets onto a recording medium such as recording paper includes a flow path unit including a nozzle that ejects ink droplets and a pressure chamber that communicates with the nozzle, and ink in the pressure chamber. Some have an actuator for applying discharge energy. The actuator applies pressure to the pressure chamber by changing the volume of the pressure chamber, and applies a piezoelectric sheet straddling a plurality of pressure chambers, a plurality of individual electrodes facing each pressure chamber, and a plurality of individual electrodes. One having a common electrode (ground electrode) to which a reference potential is applied via a piezoelectric sheet is known (see, for example, Patent Document 1). In this actuator, an electric field acts in the thickness direction on the portion of the piezoelectric sheet (piezoelectric layer) sandwiched between the individual electrode and the common electrode by applying a pulsed drive voltage to the individual electrode. And the piezoelectric sheet of this part expand | extends in the thickness direction. At this time, the volume of the pressure chamber changes and pressure (discharge energy) is applied to the ink in the pressure chamber.

Japanese Patent Laid-Open No. 2002-36568 (FIG. 1)

  In an inkjet printer, it is desired to increase the printing speed. In order to increase the printing speed, it is necessary to shorten the ink droplet ejection cycle. However, when the ink droplet ejection cycle is shortened, the ink droplets that have landed on the recording paper are dried instantaneously. It is necessary to use quick-drying ink. However, when such a fast-drying ink is used, the ink in the nozzles may increase in viscosity due to drying, and the ink ejection characteristics may deteriorate or ejection failure may occur. In order to avoid such a problem, there are cases where ejection flushing is performed by ejecting thickened ink droplets from the nozzles outside the printing area. However, when quick-drying ink is used, such ejection flushing may be performed. In a nozzle where ink droplets are not ejected frequently during printing, the viscosity of the ink increases, causing a delay in ejection of the ink droplets ejected from the nozzle, and the quality of the image recorded on the recording medium decreases. There is a risk that.

  An object of the present invention is to provide an ink jet recording apparatus capable of forming a high-quality image on a recording medium by suppressing ejection delay of ink droplets.

  An ink jet recording apparatus of the present invention includes a flow path unit in which a plurality of individual ink flow paths are formed from a common ink chamber to a nozzle through a pressure chamber, and an actuator that applies ink ejection energy to the pressure chamber. An inkjet head and a moving device that moves the recording medium relative to the inkjet head are provided. Further, a waveform output means for outputting a discharge waveform including a pulse for driving the actuator so that an ink droplet is discharged from the nozzle to the actuator, and a unit corresponding to a print resolution of an image formed on the recording medium Continuous non-ejection, which is the number of printing cycles in which no ink droplets were ejected from the nozzles continuously up to the immediately preceding printing cycle, when the time required for the relative movement of the recording medium by the distance is taken as the printing cycle A continuous non-discharge counter that counts the number of each nozzle, and a discharge history that indicates whether or not ink droplets have been discharged from the nozzle in each of a predetermined number of printing cycles that are continuous up to the immediately preceding printing cycle. Ink droplets were not ejected from the nozzles in the ejection history storage means and the ejection history stored in the ejection history storage means The non-ejection frequency corresponding to the occurrence pattern of the serial printing cycle and a non-ejection frequency detecting means for detecting for each of the nozzles. In addition, the viscosity increase of the ink in the nozzle is determined for each nozzle based on the continuous non-discharge number counted by the continuous non-discharge counter and the non-discharge frequency detected by the non-discharge frequency detecting means. And when the ink drops are ejected from the nozzles in the current printing cycle, the ink drops are ejected from the nozzles as the viscosity increase related to the nozzles determined by the viscosity increase determining means increases. Voltage control means for controlling the waveform output means so as to increase the drive voltage of the ejection waveform.

  According to the present invention, the non-ejection frequency detecting means detects the non-ejection frequency for each nozzle from the ejection history, and the viscosity increase determining means increases the ink in the nozzle based on the continuous non-ejection number and the non-ejection frequency for each nozzle. Since the viscosity is determined, it is possible to accurately grasp the viscosity increase of the ink in each nozzle. When the nozzle droplet is ejected from the nozzle, the voltage control means outputs a waveform so that the drive voltage of the ejection waveform for ejecting the ink droplet from the nozzle increases as the viscosity increase related to the nozzle increases. Control means. That is, when the viscosity increase of the ink in the nozzle is high, the ink discharge energy applied to the corresponding pressure chamber is high, and therefore, the discharge delay of the ink droplet from the nozzle can be suppressed. Thereby, a high-quality image can be formed on the recording medium.

Further, in the present invention, when the voltage control unit determines that the ink in the nozzle has increased based on the viscosity increase related to the nozzle determined by the viscosity increase determination unit, The waveform is such that the initial driving voltage that is the driving voltage of the first pulse is the highest , and the driving voltage of the subsequent pulse that follows is converged after a predetermined time or a predetermined number of pulses to become a predetermined driving voltage lower than the initial operating voltage. It is preferable to control the output means. At this time, the voltage control means may control the waveform output means so that all of the subsequent pulses become the predetermined drive voltage. According to this, the thickened ink droplet can be efficiently ejected from the nozzle. In addition, since only the initial voltage is increased, power saving can be achieved.

At this time, the voltage control means may include voltage table storage means in which the viscosity increase and the initial voltage corresponding to the viscosity increase are stored. Further, at this time, the initial viscosity voltage corresponding to the viscosity increase and the viscosity increase is stored in the voltage table storage means so that the initial voltage increases as the viscosity increase increases. preferable. According to this, the initial voltage can be determined quickly. In addition, when the voltage control unit determines that the ink in the nozzle is not thickened based on the viscosity increase related to the nozzle determined by the viscosity increase determination unit, the voltage control unit in one printing cycle The waveform output means is controlled so that the ejection waveform becomes the predetermined drive voltage after being held at the ground potential which is a reference potential for a predetermined time from the state where the discharge waveform is previously held at the predetermined drive voltage. When it is determined that the ink in the nozzle is thickened, the discharge waveform in one printing cycle is held at the ground potential for the predetermined time from the state where the discharge waveform is previously maintained at the predetermined driving voltage. Later, the waveform output means may be controlled so as to be the initial voltage instead of the drive voltage.

  In the present invention, the calculation performed when the thickening determination means determines the thickening includes at least the temperature of the inkjet head, the type of ink ejected from the nozzle, and the manufacturing eigenvalue relating to the inkjet head. A calculation of multiplying the non-ejection frequency by the first coefficient determined based on any of the above may be included.

  Further, in the present invention, the calculation performed when the viscosity increasing determining means determines the increased viscosity includes at least the temperature of the inkjet head, the type of ink ejected from the nozzle, and the manufacturing eigenvalue relating to the inkjet head. The calculation of multiplying the second coefficient determined based on any one of the continuous non-ejection numbers may be included.

  According to these, the viscosity increase is determined in consideration of the temperature of the inkjet head, the type of ink ejected from the nozzle, the eigenvalues related to the inkjet head, etc., so it is possible to grasp the more accurate viscosity increase. it can.

  In addition, in the present invention, the non-ejection frequency detection unit includes a non-ejection frequency table storage unit that stores the generation pattern of the printing cycle and the non-ejection frequency corresponding to the generation pattern of the printing cycle. It is preferable. According to this, the non-ejection frequency can be determined quickly.

  Hereinafter, preferred embodiments of the present invention will be described.

  FIG. 1 is a schematic configuration diagram of a printer (ink jet recording apparatus) according to the present embodiment. As shown in FIG. 1, a printer 101 is a line-type inkjet printer in which four inkjet heads 1 are arranged in the left-right direction in the figure, and includes a paper feeding unit 11 on the left side in the figure and a discharge unit on the right side in the figure. A paper transport unit (moving device) 13 is provided in the paper unit 12 and in the center in the figure. In the printer 101, the operation of the inkjet head 1 is controlled by the control device 16.

  A recording sheet (recording medium) P for printing is arranged in the sheet feeding unit 11. When printing is performed, the recording sheet P is paired by a pair of sheet feeding rollers 5 a and 5 b in the drawing. It is conveyed to the right. The paper transport unit 13 includes two feed rollers 6 and 7 and a transport belt 8 wound around the feed rollers 6 and 7, and the transport belt 8 rotates as the feed rollers 6 and 7 rotate. A nip roller 4 is disposed above the feed roller 7, and the conveyance belt 8 is sandwiched between the nip roller 4 and the feed roller 7. The outer peripheral surface of the transport belt 8 is a transport surface 8a for transporting the recording paper P, and the transport surface 8a is treated with adhesive silicon rubber. The recording paper P transported by the paper feed rollers 5a and 5b is transported onto the transport surface 8a while being pressed against the transport surface 8a by the nip roller 4 and the feed roller 7, and adheres to the transport surface 8a.

  The transport belt 8 transports the recording paper P transported to the transport surface 8a to the right in the drawing (moves the recording paper P relative to the inkjet head 1). At this time, the conveying belt 8 conveys the recording paper P at a constant speed so that the recording paper P moves to the right in the drawing by a unit distance of the printing resolution during a predetermined time (printing cycle).

  When a position facing the ink jet head 1 is reached, ink droplets are ejected from a nozzle 108 (see FIG. 3) described later of the head main body 2 disposed on the lower surface of the ink jet head 1 to perform printing. Here, for example, black, magenta, cyan, and yellow ink droplets are ejected from the four inkjet heads 1 in order from the left side in the drawing. Here, a platen 15 that supports the conveyance belt 8 from a surface opposite to the conveyance surface 8a is provided at a portion facing the inkjet head 1 of the conveyance belt 8, and is opposed to the inkjet head 1 on the conveyance surface 8a. The part is held horizontally. As shown in FIG. 1, the platen 13 is disposed inside the conveyor belt 8, is in contact with the inner peripheral surface thereof, and forms a predetermined gap with the lower surface of the inkjet head 1. As a result, ink droplets are ejected from the inkjet head 1 while the recording paper P is disposed horizontally.

  A peeling plate 14 is arranged on the right side of the paper transport unit 13 in the drawing, and the recording paper P is peeled from the transport belt 8 by the left end of the strip plate 14 entering between the recording paper P and the transport belt 8. The recording paper P peeled off by the peeling plate 14 is placed in the paper discharge unit 12.

  Next, the head body 2 that ejects ink droplets onto the recording paper P will be described with reference to FIGS. FIG. 2 is a plan view of the head body 2 of FIG. FIG. 3 is an enlarged view of a portion surrounded by a one-dot chain line in FIG.

  The head body 2 includes a flow path unit 9 in which a large number of pressure chambers 110 and a large number of nozzles 108 communicating with the respective pressure chambers 110 are formed. Four trapezoidal piezoelectric actuators 21 that are arranged in two rows in a staggered pattern are bonded to the upper surface of the flow path unit 9. More specifically, each piezoelectric actuator 21 is disposed such that its parallel opposing sides (upper side and lower side) are along the longitudinal direction of the flow path unit 9. Further, the oblique sides of the adjacent piezoelectric actuators 21 overlap in the width direction of the flow path unit 9.

  A portion overlapping the piezoelectric actuator 21 in a plan view of the flow path unit 9 is an ink discharge region 106. As shown in FIG. 3, a large number of nozzles 108 are regularly arranged on the surface of the ink ejection region 106, and in correspondence with this, a large number of pressure chambers 110 are formed on the upper surface of the flow path unit 9. It is arranged in a matrix. At this time, the paper P and the lower surface of the inkjet head 1 are at a predetermined distance.

  In the flow path unit 9, a manifold flow path 105 that is a common ink chamber and a sub-manifold flow path 105a that is a branch flow path are formed. Four sub-manifold channels 105 a extending in the longitudinal direction of the channel unit 9 are opposed to one ink discharge region 106. Ink is supplied to the manifold channel 105 from an ink inlet 105 b provided on the upper surface of the channel unit 9.

  Each nozzle 108 communicates with the sub-manifold channel 105a via a pressure chamber 110 and an aperture 112 having a substantially rhombus shape (rhombus shape with rounded corners) in plan view. The nozzles 108 included in the four adjacent nozzle rows extending in the longitudinal direction of the flow path unit 9 communicate with the same sub-manifold flow path 105a. 2 and 3, the piezoelectric actuator 21 is drawn by a two-dot chain line for easy understanding of the drawings, and the pressure chamber 110 and the aperture 112 to be drawn by a broken line below the piezoelectric actuator 21 are shown by solid lines. It is drawn in.

  A large number of nozzles 108 formed in the flow path unit 9 have projection points obtained by projecting all the nozzles 108 on a virtual line extending in the longitudinal direction of the flow path unit 9 from a direction orthogonal to the virtual line at 600 dpi, etc. It is formed at a position aligned with the interval.

  Next, the sectional structure of the head body 2 will be described with reference to FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. As shown in FIG. 4, the head main body 2 is obtained by bonding the flow path unit 9 and the piezoelectric actuator 21 together. The flow path unit 9 has a laminated structure in which a cavity plate 122, a base plate 123, an aperture plate 124, a supply plate 125, three manifold plates 126, 127, 128, a cover plate 129, and a nozzle plate 130 are laminated from above. have.

  The cavity plate 122 is a metal plate in which a number of substantially rhombic holes are formed in a plan view, which becomes the pressure chamber 110. The base plate 123 is a metal plate in which a number of communication holes for communicating each pressure chamber 110 and the corresponding aperture 112 and a number of communication holes for communicating each pressure chamber 110 and the corresponding nozzle 108 are formed. It is. The aperture plate 124 is a metal plate in which a large number of communication holes for communicating the holes to be the apertures 112 and the pressure chambers 110 and the corresponding nozzles 108 are formed. The supply plate 125 is a metal plate in which a plurality of communication holes for communicating each aperture 112 and the sub-manifold channel 105a and a plurality of communication holes for communicating each pressure chamber 110 and the corresponding nozzle 108 are formed. is there. The manifold plates 126, 127, and 128 are metal plates in which a hole serving as the sub-manifold channel 105 a and a plurality of communication holes for communicating each pressure chamber 110 with the corresponding nozzle 108 are formed. The cover plate 129 is a metal plate in which a large number of communication holes for communicating each pressure chamber 110 and the nozzle 108 corresponding thereto are formed. The nozzle plate 130 is a metal plate on which many nozzles 108 are formed. These nine metal plates are stacked in alignment with each other. As a result, a plurality of individual plates from the outlet of the sub-manifold 105a through the aperture 112 and the pressure chamber 110 to the nozzle 108 are disposed in the flow path unit 9. An ink flow path 132 is formed.

  Next, the piezoelectric actuator 21 will be described with reference to FIG. 5A is an enlarged view of the periphery of the piezoelectric actuator 21 of FIG. 4, and FIG. 5B is an enlarged plan view of the periphery of the individual electrode 135 of FIG. 5A. As shown in FIG. 5A, the piezoelectric actuator 21 has a laminated structure in which three piezoelectric layers 141, 142, and 143 are laminated. The piezoelectric layers 141 to 143 all have a thickness of about 15 μm, and the piezoelectric actuator 21 has a thickness of about 45 μm. Each of the piezoelectric layers 141 to 143 is a continuous layered flat plate (continuous flat plate layer) so as to be disposed across a plurality of pressure chambers 110 formed in one ink discharge region 106 in the head body 2. ing. The piezoelectric layers 141 to 143 are made of a lead zirconate titanate (PZT) ceramic material having ferroelectricity. The uppermost piezoelectric layer 141 is previously polarized in the thickness direction.

  An individual electrode 135 having a thickness of about 1 μm is formed on the upper surface of the uppermost piezoelectric layer 141. Both the individual electrode 135 and the common electrode 134 to be described later are formed by printing a conductive paste containing a metal conductive material such as Au, Ag, Ag-Pd, for example. The individual electrode 135 has a substantially rhombic planar shape that is slightly smaller than the pressure chamber 110 as shown in FIG. 5B, and most of the individual electrode 135 is opposed to the central portion of the pressure chamber 110 in plan view. It is formed to fit in the pressure chamber 110. Therefore, as shown in FIG. 3, on the uppermost piezoelectric layer 141, a large number of individual electrodes 135 are regularly arranged two-dimensionally over almost the entire area. In the present embodiment, since the individual electrode 135 is formed only on the surface of the piezoelectric actuator 21, only the piezoelectric layer 141, which is the outermost layer, includes an active region that generates piezoelectric strain due to an external electric field. Therefore, the piezoelectric actuator 21 becomes an actuator that causes unimorph deformation, and its deformation efficiency is excellent.

  One acute angle portion of the individual electrode 135 extends to a girder portion where the pressure chamber 110 is not formed in the cavity plate 22, and a land 136 is formed at the tip portion thereof. The land 136 has a substantially circular planar shape and has a thickness of about 15 μm. The land 136 is a conductive paste formed by a printing method, and the individual electrode 135 and the land 136 are electrically connected. The land 136 is electrically connected to a flexible printed circuit board (FPC) (not shown), and a driving potential is applied to the individual electrode 135 from the control device 16 via the FPC.

  Between the uppermost piezoelectric layer 141 and the lower piezoelectric layer 142, a common electrode 134 having a thickness of about 2 μm is formed on almost the entire surface. As a result, the piezoelectric layer 141 is sandwiched between the pair of electrodes of the individual electrode 135 and the common electrode 134 at a portion facing the pressure chamber 110. Note that no electrode is disposed between the piezoelectric layer 142 and the piezoelectric layer 143. The common electrode 134 is grounded in a region not shown. As a result, the common electrode 134 is equally held at the ground potential in the region facing all the pressure chambers 110.

  Here, the operation of the piezoelectric actuator 21 will be described. The individual electrode 135 is previously held at the ground potential. When a drive potential is applied to the individual electrode 135, a potential difference is generated between the individual electrode 135 and the common electrode 134, and the thickness of the portion of the piezoelectric layer 141 sandwiched between the individual electrode 135 and the common electrode 134 is increased. A direction electric field is generated. When the direction of the electric field is substantially the same as the polarization direction of the piezoelectric layer 141, this portion of the piezoelectric layer 141 contracts in the horizontal direction perpendicular to the thickness direction. At this time, the piezoelectric layers 142 and 143 function as constraining layers that are not spontaneously displaced. As a result, the piezoelectric layers 141 to 143 are deformed so as to protrude toward the pressure chamber 110 (unimorph displacement), and the volume of the pressure chamber 110 is reduced, whereby the pressure of the ink in the pressure chamber 110 increases (ink). Discharge energy is applied). Here, when the value of the driving potential is large and the deformation amount of the piezoelectric layers 141 to 143 is large, the pressure of the ink is greatly increased, so that large ink droplets are ejected from the nozzle 108 communicating with the pressure chamber 110. On the other hand, when the value of the driving potential is small and the deformation amount of the piezoelectric layers 141 to 143 is small, the ink pressure does not increase greatly, and thus a small ink droplet is ejected from the nozzle 108. In other words, if the ink viscosity is the same, the higher the drive voltage, the greater the displacement of the piezoelectric actuator 21, and a larger amount of ink droplets will be ejected at once.

  Next, the control device 16 will be described with reference to FIGS. FIG. 6 is a block diagram of the control device 16. FIG. 7 is a block diagram of the continuous non-discharge counter 151 of FIG. FIG. 8 is a block diagram of the non-ejection frequency detection circuit 152 of FIG. FIG. 9 is a block diagram of the viscosity increase calculation circuit 154 of FIG. The control device 16 is configured by a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and these function as the following units. Here, each unit shown in FIGS. 6 to 9 is provided in the control device 16 corresponding to the number of the nozzles 108. However, in order to simplify the description, only one of them is shown in FIGS. Is illustrated. During printing, the continuous non-discharge counter 151, non-discharge frequency detection circuit 152, and waveform output circuit (waveform output means) 157 indicate whether or not to discharge ink droplets corresponding to each of the plurality of nozzles 108. A print signal is input every print cycle described above.

  As shown in FIG. 6, the control device 16 includes a continuous non-discharge counter 151, a non-discharge frequency detection circuit 152, a coefficient determination unit 153, a viscosity increase calculation circuit (a viscosity increase determination means) 154, a waveform output circuit 157, and a voltage control circuit. (Voltage control means) 158 is provided. A print signal indicating whether or not to discharge ink droplets is input to the control device 16 corresponding to each of the plurality of nozzles 108.

  The continuous non-ejection counter 151 is a circuit that counts the number of continuous non-ejections, which is the number of printing cycles in which ink droplets were not ejected from the nozzles 108 continuously until the previous printing cycle, and is shown in FIG. As described above, an incrementer 161, a selector 162, and a RAM 163 are included. When the print signal is input, the incrementer 161 adds 1 to the number of continuous non-ejections stored in the RAM 163 and outputs the result to the selector 162. When the input print signal indicates that the ink droplet is not ejected, the selector 162 rewrites the continuous non-ejection number stored in the RAM 163 to a value to which 1 is added by the incrementer 161. On the other hand, if the input print signal indicates that ink droplets are to be ejected, the continuous non-ejection number stored in the RAM 163 is rewritten to zero.

  The non-ejection frequency detection circuit 152 is a circuit that determines a non-ejection frequency detection value that indicates the frequency at which ink droplets are not ejected from the nozzles 108 based on the current and the past n times (a predetermined number of continuous print signals). 8, an ejection history storage unit 171 that stores printing signals (ejection history of whether or not ink droplets are ejected) in the current and past n printing cycles, and the current and past n times A lookup table (non-ejection frequency table storage means) 172 storing non-ejection frequency detection values corresponding to the pattern of the print signal in the printing cycle, that is, the ejection pattern of the ink droplets. Then, the non-ejection frequency detection circuit 152 outputs the non-ejection frequency detection value stored in the lookup table 172 corresponding to the print signal pattern stored in the ejection history storage unit 171 to the viscosity increase calculation circuit 153. Here, the non-ejection frequency detection value stored in the look-up table 172 has a larger value as the print signal pattern in the current and past n print cycles easily increases the viscosity of the ink in the nozzle 108. Yes. As described above, since the non-ejection frequency detection value corresponding to the print signal pattern in the current and the past n printing cycles is stored in the lookup table 172, the non-ejection frequency detection circuit 152 detects the non-ejection frequency. The value can be determined quickly.

  The coefficient determination unit 153 determines the values of the first coefficient W1 and the second coefficient W2, which are values indicating the degree of influence of the non-ejection frequency detection value and the number of continuous non-ejections on the viscosity increase of the ink in the nozzle 108. Here, the first coefficient W1 and the second coefficient W2 are values determined based on the type of ink ejected from the nozzle 108, the characteristic value on the structure of the inkjet head 1, and the like. The larger the non-ejection frequency detection value, the greater the increase in the viscosity of the ink in the nozzle 108. The structural eigenvalues are determined from the piezoelectric characteristics of each piezoelectric actuator 21 and the fluid characteristics resulting from the assembly error of the flow path unit 9 and the processing error when forming the flow path. Related to properties.

  The viscosity increase calculation circuit 154 is a circuit that calculates a viscosity increase indicating the degree of ink viscosity increase in the nozzle 108, and includes two multipliers 181, 182 and an adder 183 as shown in FIG. ing. The multiplier 181 outputs a value obtained by multiplying the non-ejection frequency detection value and the first coefficient W1 to the adder 183. The multiplier 182 outputs a value obtained by multiplying the number of continuous non-ejections and the second coefficient W2 to the adder 183. The adder 183 calculates the viscosity increase by adding the values output from the multipliers 181 and 182 to each other, and outputs it to the voltage control circuit 158. That is, the calculation performed when the viscosity increase calculation circuit 154 calculates the viscosity increase is an operation of multiplying the non-ejection frequency detection value and the first coefficient, and the number of continuous non-ejections and the second coefficient W2. Is included.

  As described above, since the viscosity increase of the nozzle 108 is calculated based on the non-discharge frequency detection value and the continuous non-discharge number, the viscosity increase can be accurately grasped. Further, the first coefficient W1 and the second coefficient W2 determined based on the temperature of the ink jet head 1, the type of ink ejected from the nozzle 108, and the manufacturing eigenvalues related to the ink jet head 1 are set as the non-ejection frequency detection value and the continuous value, respectively. Since the viscosity increase is calculated by multiplying the number of ejection failures and adding these values, the viscosity increase can be grasped more accurately.

  The waveform output circuit 157 outputs a drive waveform for applying a drive potential to the individual electrode 153 (piezoelectric actuator 21). FIG. 10 is a diagram illustrating a drive waveform output from the waveform output circuit 157. The waveform output circuit 157 is shown in FIG. 10A as a normal drive waveform for causing ink droplets to be ejected from the nozzle 108 when a print signal indicating ejection of ink droplets from the nozzle 108 is input. Such a waveform having a pulse of the potential V 1 is generated and output to the corresponding individual electrode 135. This pulse waveform is for ejecting a single ink droplet, and is once changed from being held at the ground potential in advance to once at the potential V1 for a predetermined time and then returning to the ground potential again. The potential V1 is determined so that when applied to the individual electrode 135, a predetermined amount of ink droplets are ejected if the ink has a normal viscosity.

  The voltage control circuit 158 controls the voltage of the drive waveform output from the waveform output circuit 157 based on the ink viscosity increase in the nozzle 108 output from the viscosity increase calculation circuit 154. Specifically, as shown in FIG. 10B, the voltage of the drive waveform is controlled so that the initial voltage, which is the drive voltage at the start of output of the drive waveform, becomes the highest. FIG. 10B schematically shows a change in potential of each pulse following when the initial voltage is V2 (> V1). The later pulse, the potential becomes lower than V2, and converges to the potential V1 after a predetermined time or a predetermined number of pulses. The voltage control circuit 158 shown in FIG. 6 has a voltage table storage unit 158a, and the voltage table storage unit 158a stores the ink viscosity increase and the initial voltage corresponding to each viscosity increase as a table. This table is set so that the initial voltage corresponding to the thickening increases as the thickening increases. The voltage control circuit 158 refers to the table stored in the voltage table storage unit 158a to determine an initial voltage corresponding to the viscosity increase output from the viscosity increase calculation circuit 154, and the waveform output circuit 157 determines the initial voltage. Is output as a drive voltage. The initial voltage is prepared in several stages corresponding to the viscosity increase, and the drive waveform has a longer time for the potential to become higher than V1 as the initial voltage increases. When the time during which the potential is higher than V1 becomes longer, the time during which the piezoelectric actuator 21 is displaced unimorph longer than when the normal drive waveform is output to the individual electrode 135 becomes longer. Thereby, the ink ejection energy applied to the pressure chamber 110 is increased, and the ejection delay of the ink droplets is suppressed even when the viscosity increase of the ink in the nozzle 108 is high. Further, the volume of the ink droplets is equivalent to that when ink having a normal viscosity is ejected.

  According to the embodiment described above, the non-ejection frequency detection circuit 152 detects the non-ejection frequency for each nozzle 108 from the ejection history stored in the ejection history storage unit 171, and the viscosity increase calculation circuit 154 detects each nozzle 108. Since the viscosity increase of the ink in the nozzle 108 is determined based on the number of continuous non-discharges and the frequency of non-discharge, the increase in the viscosity of the ink in each nozzle 108 can be accurately grasped. When the nozzle droplet is ejected from the nozzle 108, the voltage control circuit 158 increases the initial voltage of the drive waveform for ejecting the ink droplet from the nozzle 108 as the viscosity increase related to the nozzle 108 increases. Since the waveform output circuit 157 is controlled at the same time, even when the viscosity increase of the ink in the nozzle 108 is high, there is no delay in the ejection of ink droplets from the nozzle 108, and the paper P has a high quality. An image can be formed.

  In particular, since the voltage control circuit 158 controls the waveform output circuit 157 so that the initial voltage of the drive waveform becomes high, it is possible to efficiently eject thickened ink droplets from the nozzles 108.

  Further, since the voltage control circuit 158 determines the initial voltage with reference to the voltage table storage unit 158a, the initial voltage can be determined quickly.

  Further, the viscosity increase calculation circuit 154 uses the first coefficient W1 and the second coefficient W2 determined based on the temperature of the inkjet head 1, the type of ink ejected from the nozzles 108, and the manufacturing eigenvalues related to the inkjet head, respectively. By calculating the viscosity increase by correcting the non-ejection frequency and the number of continuous non-ejections, the temperature of the inkjet head 1, the type of ink ejected from the nozzles 108, and the manufacturing specific values related to the inkjet head 1 are taken into consideration. Since the viscosity increase is determined, the more accurate viscosity increase can be grasped.

  Further, since the non-ejection frequency detection circuit 152 stores the non-ejection frequency detection values corresponding to the current and past n print signals in the lookup table 172, the non-ejection frequency detection circuit 152 can quickly The detection value can be determined.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made as long as they are described in the claims. For example, in the present embodiment, the initial voltage and the subsequent voltage are increased according to the viscosity increase, but only the initial voltage may be increased. Thereby, power saving can be achieved.

  In the present embodiment, the first coefficient W1 and the second coefficient W2 are determined based on the temperature of the inkjet head 1, the type of ink ejected from the nozzle 108, and the manufacturing eigenvalues related to the inkjet head 1. The first coefficient and the second coefficient may be determined based on only some of these.

  Further, in the present embodiment, the calculation performed when the thickening calculation circuit 154 calculates the thickening, the calculation of multiplying the non-ejection frequency detection value and the first coefficient W1, and the number of continuous non-discharges and the second coefficient Although the calculation of multiplying by W2 was included, the viscosity increase may be calculated by a calculation including only one of them. Alternatively, the calculation performed when calculating the viscosity increase does not include any of these calculations, and the viscosity increase may be determined by another calculation using the non-discharge frequency detection value and the continuous non-discharge number.

  In the present embodiment, the non-ejection frequency detection circuit 152 corresponds to the printing signals stored in the ejection history storage unit 171 in the current and past n printing cycles and stored in the lookup table 172. Although the ejection frequency detection value is output, the present invention is not limited to this, and the non-ejection frequency detection circuit 152 uses the print signal based on the print signal stored in the ejection history storage unit 171 in the current and past n printing cycles. The non-ejection frequency may be calculated.

  Further, in the present embodiment, as shown in FIG. 10A, the drive waveform changes from the ground potential to the potential V1 in one printing cycle. On the contrary, as shown in FIG. In addition, there may be a change from a state in which the potential V1 is maintained in advance to a state where the ground potential is once maintained for a predetermined time and then returned to the potential V1 again. In this case, since the ink droplet is ejected at the timing when the potential returns to the potential V1 again from the ground potential, when the viscosity increases, the value of the potential that returns from the ground potential is changed as shown in FIG. In other words, when the potential V1 is maintained in advance, the ground potential is once held for a predetermined time, and when returning to the predetermined potential again, the initial voltage V2 is changed. In the drive waveform that follows, the potential that recovers from the ground potential is gradually brought closer to the potential V1.

  In this embodiment, the example in which the present invention is applied to the printer 101 having the line-type inkjet head 1 has been described. However, the present invention can also be applied to a printer having a structure different from that of the present embodiment. is there.

1 is a schematic configuration diagram of a printer according to an embodiment of the present invention. FIG. 2 is a plan view of the head body of FIG. 1. FIG. 3 is an enlarged view of a portion surrounded by an alternate long and short dash line in FIG. 2. It is the IV-IV sectional view taken on the line of FIG. (A) is an enlarged view of the periphery of the piezoelectric actuator of FIG. 4, and (b) is a plan view of the individual electrode of (a). It is a block diagram of the control apparatus of FIG. It is a block diagram of the continuous non-discharge counter of FIG. It is a block diagram of the non-ejection frequency detection circuit of FIG. It is a block diagram of the viscosity increase calculation circuit of FIG. 7A and 7B are diagrams illustrating waveforms output from the waveform output circuit of FIG. 6, in which FIG. 7A is a normal drive waveform, and FIG. 7B is a schematic diagram illustrating a change in initial voltage and subsequent potential. It is a figure which shows the modification of the waveform output from a waveform output circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet head 6, 7 Feed roller 8 Conveyance belt 9 Flow path unit 21 Piezoelectric actuator 101 Printer 105 Manifold flow path 105a Sub manifold flow path 108 Nozzle 110 Pressure chamber 132 Individual ink flow path 151 Continuous non-discharge counter 152 Non-discharge frequency detection circuit 154 Viscosity increase calculation circuit 157 Waveform output circuit 158 Voltage control circuit 171 Discharge history storage unit 172 Look-up table

Claims (9)

A flow path unit in which a plurality of individual ink flow paths from a common ink chamber to a nozzle through a pressure chamber are formed, and an inkjet head having an actuator for applying ink ejection energy to the pressure chamber;
A moving device for moving the recording medium relative to the inkjet head;
Waveform output means for outputting to the actuator a discharge waveform including a pulse for driving the actuator so that an ink droplet is discharged from the nozzle;
When the time required for the relative movement of the recording medium by a unit distance corresponding to the printing resolution of the image formed on the recording medium is defined as a printing cycle, the ink from the nozzles continuously until the immediately preceding printing cycle. A continuous non-discharge counter that counts the number of continuous non-discharges, which is the number of printing cycles in which no droplets were discharged, for each nozzle;
An ejection history storage means for storing, for each nozzle, an ejection history as to whether or not an ink droplet has been ejected from the nozzle in each of a predetermined number of printing cycles continuously up to the previous printing cycle
A non-ejection frequency detection unit that detects, for each nozzle, a non-ejection frequency corresponding to a generation pattern of the printing cycle in which ink droplets were not ejected from the nozzles in the ejection history stored in the ejection history storage unit;
Based on the number of continuous non-ejections counted by the continuous non-ejection counter and the non-ejection frequency detected by the non-ejection frequency detecting means, the viscosity increase is determined for each nozzle based on the non-ejection frequency. A determination means;
When ink droplets are ejected from the nozzles in the current printing cycle, the ejection waveform for ejecting ink droplets from the nozzles increases as the viscosity increase for the nozzles determined by the viscosity increase determining unit increases. An ink jet recording apparatus comprising: voltage control means for controlling the waveform output means so that the drive voltage becomes high. When the voltage control unit determines that the ink in the nozzle has increased based on the viscosity increase related to the nozzle determined by the viscosity increase determination unit, the drive voltage of the leading pulse in the ejection waveform Controlling the waveform output means so that the initial drive voltage is the highest and the drive voltage of the subsequent pulse that follows is converged after a predetermined time or a predetermined number of pulses to be a predetermined drive voltage lower than the initial drive voltage. The inkjet recording apparatus according to claim 1, wherein The inkjet recording apparatus according to claim 2, wherein the voltage control unit controls the waveform output unit so that all of the subsequent pulses become the predetermined drive voltage. 4. The ink jet recording apparatus according to claim 2 , wherein the voltage control unit includes a voltage table storage unit in which the viscosity increase and the initial voltage corresponding to the viscosity increase are stored. The initial voltage corresponding to the viscosity increase and the initial viscosity is stored in the voltage table storage unit so that the initial voltage increases as the viscosity increases. 4. An ink jet recording apparatus according to 4. When the voltage control unit determines that the ink in the nozzle is not thickened based on the viscosity increase related to the nozzle determined by the viscosity increase determination unit, the discharge waveform in one printing cycle. Is controlled in advance so that the waveform output means is set to the predetermined drive voltage after being held at the ground potential, which is a reference potential, for a predetermined time after being held at the predetermined drive voltage in advance. When the ink is thickened, the ejection waveform in one printing cycle is held at the ground potential for the predetermined time from the state where the ejection waveform is maintained at the predetermined driving voltage in advance. The inkjet recording according to any one of claims 2 to 5, wherein the waveform output means is controlled so as to be the initial voltage instead of the drive voltage. Location. The calculation performed by the thickening determining means when determining the thickening is determined based on at least one of the temperature of the inkjet head, the type of ink ejected from the nozzle, and a manufacturing specific value related to the inkjet head. an ink jet recording apparatus according to any one of claims 1 to 6, characterized in that it contains the operation that the first coefficient is multiplied to the non-ejection frequency was. The calculation performed by the thickening determining means when determining the thickening is determined based on at least one of the temperature of the inkjet head, the type of ink ejected from the nozzle, and a manufacturing specific value related to the inkjet head. an ink jet recording apparatus according to any one of claims 1 to 7, the second coefficient, characterized in that it contains operations that multiply to the continuous non-ejection number. 2. The non-ejection frequency detection unit includes a non-ejection frequency table storage unit that stores the generation pattern of the printing cycle and the non-ejection frequency corresponding to the generation pattern of the printing cycle. The inkjet recording device according to any one of 7 to 7 .

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