JP4894965B2 - Inkjet printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress worsening of an ink discharging characteristic and poor discharge, and to attain saving of power. <P>SOLUTION: An inkjet head has an actuator unit which holds a piezoelectric sheet between individual electrodes related to pressure chambers corresponding to nozzles and a ground electrode, and a driver IC which selectively outputs a discharging waveform and a flushing discharging waveform shorter in pulse period than the discharging waveform. A power supply device 16 which supplies power to the driver IC has a current limiting circuit 85 which limits a current supplied by the power supply device 16 when the power supply device 16 is going to supply the current that exceeds a current to be supplied when the driver IC outputs the discharging waveform to all of the individual electrodes and that is not lower than an upper limit current not fulfilling a current to be supplied when the driver IC outputs the flushing discharging waveform to all of the individual electrodes. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

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

  An inkjet head included in an inkjet printer that ejects ink droplets onto a recording medium such as recording paper includes a flow path unit that includes a nozzle that ejects ink droplets and a pressure chamber that communicates with the nozzle, and ejects ink in the pressure chamber. Some have an actuator that imparts energy. The actuator applies pressure to the pressure chamber by changing the volume of the pressure chamber, a piezoelectric sheet (piezoelectric layer) straddling the plurality of pressure chambers, a plurality of individual electrodes facing each pressure chamber, a plurality of There is known one having a common electrode (ground electrode) to which a reference potential is applied to each individual electrode via a piezoelectric sheet (see, for example, Patent Document 1). In this actuator, an electric field acts on the portion of the piezoelectric sheet sandwiched between the individual electrode and the common electrode by applying a pulse-like drive signal to the individual electrode, and this portion The piezoelectric sheet is stretched 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. When such a fast-drying ink is used, the ink in the nozzles may increase in viscosity due to drying, thereby deteriorating ink ejection characteristics or causing ejection failure. In order to avoid such a problem, it is known to perform discharge flushing in which thickened ink is discharged from the nozzle. However, when the frequency of discharge flushing is high, a large amount of ink is wasted.

  Therefore, by applying a drive signal having a pulse width narrower than the pulse width of the drive signal for ejecting ink droplets from the nozzle to the individual electrodes, the actuator is driven to the extent that ink droplets are not ejected from the nozzles, and the ink in the nozzles is discharged. Non-ejection flushing with stirring may be performed. However, such non-ejection flushing requires a greater number of actuators to be driven than in the case of ejection flushing, resulting in increased power consumption of the ink jet printer.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an ink jet printer that can suppress deterioration of ink ejection characteristics and ejection failure and can save power.

The ink jet printer of the present invention is provided with 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, an individual electrode associated with the pressure chamber, and a reference potential. And a waveform including an actuator including a piezoelectric layer disposed between the ground electrode and the individual electrode and the ground electrode, and a pulse for driving the actuator so that an ink droplet is ejected from the nozzle. A first waveform including a pulse for driving the actuator, and a pulse having a pulse width smaller than the pulse of the first waveform and driving the actuator in a range in which an ink droplet is not ejected from the nozzle , greater power than the pulse multiple pulse unrealized said first waveform is continuous with a narrower spacing than the spacing of the first waveform A waveform outputting means for outputting selectively the individual electrodes and the second waveform to be consumed, the AC / DC converter power from an external power source is supplied, the input from the AC / DC converter current is less than the upper limit current When the current input from the AC / DC converter is equal to or greater than the upper limit current, the current is limited and output to the waveform output means. The upper limit current exceeds a current to be supplied when the waveform output means outputs the first waveform to all the individual electrodes, and all of the waveform output means wherein is intended less than the current to be supplied when the output the second waveform at the same driving voltage and pulse of the first waveform to the individual electrodes, the current limiting means, the waveform output hand When the second waveform is output to all the individual electrodes, the current supplied from the AC / DC converter is limited and output by limiting the current to be supplied to the waveform output means. The voltage of the second waveform pulse is set to a voltage at which no ink droplet is ejected from the nozzle .

  At this time, the first waveform has a frequency at which a current less than the upper limit current is consumed when the actuator is driven by being supplied to all the individual electrodes, and the second waveform is the first waveform. It has a frequency higher than one waveform, and preferably has a frequency at which a current equal to or higher than the upper limit current is consumed when the actuator is driven by being supplied to all the individual electrodes.

  According to the present invention, when the non-ejection flushing is performed, if the waveform output unit tries to output the second waveform to all the individual electrodes, the current limiting unit limits the current supplied to the waveform output unit. As a result, it is possible to suppress the deterioration of the ink discharge characteristics and the discharge failure and to save the power of the ink jet printer.

From another viewpoint, the ink jet printer of the present invention includes a transport device that transports a recording medium, and 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. An actuator including an individual electrode associated with the pressure chamber, a ground electrode to which a reference potential is applied, and a piezoelectric layer disposed between the individual electrode and the ground electrode, and the recording medium. Multiple types in which different amounts of ink are ejected from the nozzles within the one printing cycle, where the time required for the recording medium to be conveyed by a unit distance corresponding to the printing resolution of the image to be printed is defined as a printing cycle a waveform, and the waveform output means for outputting selectively the individual electrodes a plurality of discharge waveform including a pulse for driving the actuator, leaving the waveform Control means for controlling the means, AC / DC converter supplied with power from an external power source, and output of the waveform without limiting the current when the current input from the AC / DC converter is less than the upper limit current Current limiting means for limiting the current to be output to the waveform output means when the current input from the AC / DC converter is equal to or higher than the upper limit current, and the control means When driving the actuator so that ink droplets are ejected from some of the nozzles, the plurality of ejections are performed on some of the individual electrodes corresponding to the some of the nozzles within one printing cycle. When controlling the actuator to output any of the waveforms and driving the actuator so that ink droplets are ejected from all the nozzles, there are few A discharge waveform corresponding to an amount equal to or less than the second largest discharge amount of the plurality of discharge waveforms is output to one of the individual electrodes, and the plurality of discharges is output to the other individual electrode. When controlling the actuator to output any one of the waveforms and driving the actuator in a range where ink droplets are not ejected from all the nozzles, the plurality of ejections for all the individual electrodes within one printing cycle Control is performed so as to output an ejection waveform corresponding to the largest ink ejection amount among the waveforms, and the waveform output means causes the upper limit current to eject ink droplets from all the nozzles within the one printing cycle. Outputs the ejection waveform corresponding to an amount equal to or less than the second largest amount of ink ejection for at least one of the individual electrodes and outputs the largest amount for the other individual electrodes. The current to be supplied when the ejection waveform corresponding to the ink ejection amount is output exceeds the current to be supplied, and the waveform output means outputs the ejection waveform corresponding to the largest ink ejection amount for all the individual electrodes. The current limiting unit is configured to discharge the discharge of the waveform output unit corresponding to the largest ink discharge amount for all the individual electrodes within the one printing cycle. When outputting the waveform, the current input from the AC / DC converter is limited and output, thereby reducing the voltage of the power supplied to the waveform output means, and setting the drive voltage of the pulse of the ejection waveform to the The voltage is such that no ink droplet is ejected from the nozzle .

At this time , when ink droplets are ejected from all the nozzles within the one printing cycle, the waveform output means ejects an amount of ink equal to or less than the second largest ink ejection amount to all the individual electrodes. it is good preferable that outputs the discharge waveform when.

According to the present invention, in order to perform non-ejection flushing, when the waveform output means tries to output the ejection waveform to all the individual electrodes, the current limiting means limits the current supplied to the waveform output means, The actuator is driven in a range where the drive voltage of the discharge waveform does not discharge ink droplets from the nozzles. In this way, the current limiting means limits the current output from the AC / DC converter when non-ejection flushing is performed, so that deterioration of ink ejection characteristics and ejection failure are suppressed and power consumption of the inkjet printer is reduced. be able to. Further, the current limiting means functioning as an overcurrent protection device generates a voltage control circuit for reducing the drive voltage and a waveform for non-ejection flushing in order to lower the drive voltage of the drive signal when non-ejection flushing is performed. The waveform generation circuit is not necessary, and the cost of the ink jet printer can be reduced.

  According to the present invention, when the non-ejection flushing is performed, if the waveform output unit tries to output the second waveform to all the individual electrodes, the current limiting unit limits the current supplied to the waveform output unit. As a result, it is possible to suppress the deterioration of the ink discharge characteristics and the discharge failure and to save the power of the ink jet printer.

1 is an external side view of an inkjet head according to an embodiment of the present invention. It is sectional drawing along the transversal direction of the inkjet head shown in FIG. FIG. 3 is a plan view of the head main body shown in FIG. 2. It is an enlarged view of the area | region enclosed with the dashed-dotted line shown in FIG. It is the VV sectional view taken on the line shown in FIG. It is an enlarged view of the actuator unit shown in FIG. FIG. 3 is a waveform diagram of a drive signal that the driver IC shown in FIG. 2 is to output. It is a functional block diagram of the power supply device shown in FIG. It is a graph which shows the electric power supply characteristic of the power supply device shown in FIG. FIG. 3 is a waveform diagram of drive signals actually output from the driver IC shown in FIG. 2. It is a top view of the head main body shown in FIG. 2 for demonstrating a 1st modification. It is a functional block diagram of the power supply device which the inkjet printer which concerns on 2nd Embodiment has. It is a graph which shows the electric power supply characteristic of the power supply device shown in FIG. It is a functional block diagram of the power supply device which the inkjet printer which concerns on 3rd Embodiment has. 15 is a graph showing characteristics of power supplied from the power supply device shown in FIG. 14 to the driver IC 52.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic side view showing an overall configuration of an ink jet printer according to a first embodiment of the present invention. As shown in FIG. 1, the inkjet printer 101 is a color inkjet printer having four inkjet heads 1. The ink jet printer 101 includes a power supply device 16 that supplies power to the ink jet head 1. The inkjet printer 101 includes a paper feeding unit 11 on the left side in the drawing and a paper discharge unit 12 on the right side in the drawing.

  Inside the ink jet printer 101, a paper transport path is formed through which paper (recording medium) P is transported from the paper supply unit 11 toward the paper discharge unit 12. A pair of feed rollers 5a and 5b for nipping and conveying the paper are arranged immediately downstream of the paper supply unit 11. The pair of feed rollers 5a and 5b are for feeding the paper P from the paper feeding unit 11 to the right in the drawing. In an intermediate portion of the paper conveyance path, two belt rollers 6 and 7, an endless conveyance belt 8 wound around the rollers 6 and 7, and an area surrounded by the conveyance belt 8 A belt conveyance mechanism (paper conveyance mechanism) 13 including a platen 15 disposed at a position facing the inkjet head 1 is provided. The platen 15 supports the conveyance belt 8 so that the conveyance belt 8 does not bend downward in a region facing the inkjet head 1. A nip roller 4 is disposed at a position facing the belt roller 7. The nip roller 4 presses the sheet P fed from the sheet feeding unit 11 by the feed rollers 5 a and 5 b against the outer peripheral surface 8 a of the transport belt 8.

  The conveyor belt 8 is driven by a conveyor motor (not shown) rotating the belt roller 6. Thereby, the conveyance belt 8 conveys the paper P pressed against the outer peripheral surface 8 a by the nip roller 4 toward the paper discharge unit 12 while being adhesively held.

  A peeling mechanism 14 is provided immediately downstream of the conveying belt 8 along the sheet conveying path. The peeling mechanism 14 is configured to peel the paper P adhered to the outer peripheral surface 8a of the conveyor belt 8 from the outer peripheral surface 8a and send it to the right paper discharge unit 12 on the left side in the drawing. .

  The four inkjet heads 1 are provided side by side along the transport direction of the paper P, corresponding to four colors of ink (magenta, yellow, cyan, and black). That is, the ink jet printer 101 is a line printer. Each of the four inkjet heads 1 has a head body 2 at the lower end thereof. The head main body 2 has an elongated rectangular parallelepiped shape that is long in a direction orthogonal to the transport direction. Further, the bottom surface of the head body 2 is an ink ejection surface 2 a that faces the outer peripheral surface 8 a of the transport belt 8. When the paper P transported by the transport belt 8 sequentially passes immediately below the four head bodies 2, each color of each color is directed from the ink ejection surface 2 a toward the printing area formed on the upper surface of the paper P, that is, the printing surface. Ink droplets are ejected. Thereby, a desired color image can be formed in the print area of the paper P.

  Next, the inkjet head 1 will be described in detail with reference to FIG. FIG. 2 is a cross-sectional view of the inkjet head 1 along the short direction. As shown in FIG. 2, the inkjet head 1 includes a head body 2 including a flow path unit 9 and an actuator unit 21, a reservoir unit 71 that is disposed on the upper surface of the head body 2 and supplies ink to the head body 2, A driver IC (waveform output means) 52 for generating a drive signal for driving the actuator unit 21 is mounted on the surface thereof, a COF (Chip On Film) 50, a substrate 54 electrically connected to the COF 50, and the actuator unit 21, A side cover 53 and a head cover 55 are provided to cover the reservoir unit 71, the COF 50, and the substrate 54, and prevent ink and ink mist from entering from the outside.

  The reservoir unit 71 is formed by stacking four plates 91 to 94 that are aligned with each other. Inside the reservoir unit 71, an ink inflow channel (not shown), an ink reservoir 61, and 10 ink outflow flows are provided. The passages 62 are formed so as to communicate with each other. In FIG. 2, only one ink outflow channel 62 appears. The ink inflow channel is a channel into which ink from an ink tank (not shown) flows. The ink reservoir 61 communicates with the ink inflow channel and the ink outflow channel 62. The ink outflow channel 62 communicates with the channel unit 9 via an ink supply port 105 b (see FIG. 3) formed on the upper surface of the channel unit 9. Ink from the ink tank flows into the ink reservoir 61 through the ink inflow channel. The ink flowing into the ink reservoir 61 passes through the ink outflow channel 62 and is supplied to the channel unit 9 via the ink supply port 105b.

  Further, the plate 94 has a recess 94a. In the portion of the plate 94 where the concave portion 94a is formed, a gap is formed between the plate unit 94 and the flow path unit 9, and the actuator unit 21 is disposed in this gap.

  The COF 50 is bonded to the upper surface of the actuator unit 21 in the vicinity of one end thereof so that a wiring (not shown) formed on the surface is electrically connected to an individual electrode 135 and a common electrode 134 which will be described later. Further, the COF 50 is drawn upward from the upper surface of the actuator unit 21 so as to pass between the side cover 53 and the reservoir unit 71, and the other end thereof is connected to the substrate 54 via the connector 54a. At this time, the driver IC 52 of the COF 50 is urged toward the side cover 53 by the sponge 82 attached to the side surface of the reservoir unit 71. The driver IC 52 is thermally coupled to the side cover 53 by being in close contact with the inner surface of the side cover 53 via the heat dissipation sheet 81. Thereby, heat from the driver IC 52 is radiated to the outside through the side cover 53.

  The board 54 controls the drive of the actuator unit 21 by outputting a drive signal to the actuator unit 21 via the COF 50 based on an instruction from a host control device (not shown).

  The side cover 53 is a metal plate member attached so as to extend upward from the vicinity of both ends in the lateral direction on the upper surface of the flow path unit 9. The head cover 55 is attached above the side cover 53 so as to seal the space above the flow path unit 9. As described above, the reservoir unit 71, the COF 50, and the substrate 54 are disposed in the space surrounded by the two side covers 53 and the head cover 55. A sealing member 56 made of a silicon resin material or the like is applied to a connection portion between the side cover 53 and the flow path unit 9 and a fitting portion between the side cover 53 and the head cover 55. This more reliably prevents ink and ink mist from entering from the outside.

  Next, the head body 2 will be described with reference to FIGS. FIG. 3 is a plan view of the head body 2. FIG. 4 is an enlarged view of a region surrounded by a one-dot chain line in FIG. In FIG. 4, for convenience of explanation, the pressure chamber 110, the aperture 112, and the nozzle 108 that are to be drawn by broken lines below the actuator unit 21 are drawn by solid lines. FIG. 5 is a partial cross-sectional view taken along line VV shown in FIG. 6A is an enlarged cross-sectional view of the actuator unit 21, and FIG. 6B is a plan view showing individual electrodes arranged on the surface of the actuator unit 21 in FIG. 6A.

  As shown in FIG. 3, the head body 2 includes a flow path unit 9 and four actuator units 21 fixed to the upper surface 9 a of the flow path unit 9. As shown in FIG. 4, the actuator unit 21 includes a plurality of actuators provided facing the pressure chamber 110 formed in the flow path unit 9, and selectively ejects energy into the ink in the pressure chamber 110. It has the function to give.

  The flow path unit 9 has a rectangular parallelepiped shape that has substantially the same planar shape as the plate 94 of the reservoir unit 71. A total of ten ink supply ports 105b are opened on the upper surface 9a of the flow path unit 9 corresponding to the ink outflow flow path 62 (see FIG. 2) of the reservoir unit 71. A manifold channel 105 communicating with the ink supply port 105 b and a sub-manifold channel 105 a branched from the manifold channel 105 are formed inside the channel unit 9. As shown in FIGS. 4 and 5, an ink discharge surface 2 a in which a large number of nozzles 108 are arranged in a matrix is formed on the lower surface of the flow path unit 9. A large number of pressure chambers 110 are also arranged in a matrix like the nozzles 108 on the fixed surface of the actuator unit 21 in the flow path unit 9.

  In the present embodiment, 16 rows of pressure chambers 110 arranged at equal intervals in the longitudinal direction of the flow path unit 9 are arranged in parallel to each other in the short direction. The number of pressure chambers 110 included in each pressure chamber row is arranged so as to gradually decrease from the long side toward the short side corresponding to the outer shape (trapezoidal shape) of the actuator unit 21 described later. Yes. The nozzle 108 is also arranged in the same manner.

  As shown in FIG. 5, the flow path unit 9 includes a cavity plate 122, a base plate 123, an aperture plate 124, a supply plate 125, manifold plates 126, 127, and 128, a cover plate 129, and a nozzle plate 130 in order from the top. It consists of nine metal plates such as stainless steel. These plates 122 to 130 have a rectangular plane elongated in the main scanning direction.

  The cavity plate 122 is formed with a large number of through holes corresponding to the ink supply ports 105b (see FIG. 3) and a substantially rhombic through hole corresponding to the pressure chamber 110. In the base plate 123, a communication hole between the pressure chamber 110 and the aperture 112 and a communication hole between the pressure chamber 110 and the nozzle 108 are formed for each pressure chamber 110, and the communication between the ink supply port 105 b and the manifold channel 105 is formed. A hole (not shown) is formed. The aperture plate 124 is formed with a through hole serving as the aperture 112 for each pressure chamber 110 and a communication hole between the pressure chamber 110 and the nozzle 108, and a communication hole between the ink supply port 105 b and the manifold channel 105 (see FIG. (Not shown) is formed. In the supply plate 125, a communication hole between the aperture 112 and the sub manifold channel 105 a and a communication hole between the pressure chamber 110 and the nozzle 108 are formed for each pressure chamber 110, and the ink supply port 105 b and the manifold channel 105 are formed. A communication hole (not shown) is formed. In the manifold plates 126, 127, and 128, a communication hole between the pressure chamber 110 and the nozzle 108 for each pressure chamber 110, and a through-hole that is connected to each other at the time of stacking to form the manifold channel 105 and the sub-manifold channel 105a are formed. Has been. In the cover plate 129, a communication hole between the pressure chamber 110 and the nozzle 108 is formed for each pressure chamber 110. In the nozzle plate 130, holes corresponding to the nozzles 108 are formed for each pressure chamber 110.

  By laminating these plates 122 to 130 while being aligned with each other, the nozzle 108 in the flow path unit 9 passes from the manifold flow path 105 to the sub manifold flow path 105a and from the outlet of the sub manifold flow path 105a through the pressure chamber 110. A large number of individual ink channels 132 are formed.

  Next, the ink flow in the flow path unit 9 will be described. As shown in FIGS. 3 to 5, the ink supplied from the reservoir unit 71 into the flow path unit 9 through the ink supply port 105 b is branched from the manifold flow path 105 to the sub-manifold flow path 105 a. The ink in the sub-manifold channel 105a flows into each individual ink channel 132 and reaches the nozzle 108 through the aperture 112 and the pressure chamber 110 functioning as a throttle.

  The actuator unit 21 will be described. As shown in FIG. 3, each of the four actuator units 21 has a trapezoidal planar shape, and is arranged in a staggered manner so as to avoid the ink supply ports 105b. Furthermore, the parallel opposing sides of each actuator unit 21 are along the longitudinal direction of the flow path unit 9, and the oblique sides of the adjacent actuator units 21 overlap each other in the width direction (sub-scanning direction) of the flow path unit 9. Yes.

  As shown in FIG. 6A, the actuator unit 21 is composed of three piezoelectric sheets (piezoelectric layers) 141 to 143 made of a lead zirconate titanate (PZT) ceramic material having ferroelectricity. Yes. An individual electrode 135 is formed at a position facing the pressure chamber 110 on the uppermost piezoelectric sheet 141. A common electrode (ground electrode) 134 formed on the entire surface of the sheet is interposed between the uppermost piezoelectric sheet 141 and the lower piezoelectric sheet 142. As shown in FIG. 6B, the individual electrode 135 has a substantially rhombic planar shape similar to the pressure chamber 110. One of the acute angle portions of the substantially rhomboid individual electrode 135 is extended, and a circular land 136 electrically connected to the individual electrode 135 is provided at the tip thereof.

  The common electrode 134 is equally applied with the ground potential (reference potential) in the region corresponding to all the pressure chambers 110. On the other hand, the individual electrode 135 is electrically connected to each terminal of the driver IC 52 via each land 136 and the internal wiring of the COF 50, and a drive signal from the driver IC 52 is selectively input. . That is, in the actuator unit 21, a portion sandwiched between the individual electrode 135 and the pressure chamber 110 functions as an individual actuator, and a plurality of actuators corresponding to the number of pressure chambers 110 are formed.

  Here, a driving method of the actuator unit 21 will be described. The piezoelectric sheet 141 is polarized in the thickness direction. When an electric field is applied to the piezoelectric sheet 141 by setting the individual electrode 135 to a potential different from that of the common electrode 134, the electric field application portion of the piezoelectric sheet 141 has a piezoelectric effect. Acts as an active part that is distorted by When the electric field and the polarization direction are the same, the active portion expands in the thickness direction and contracts in the surface direction. At this time, the amount of displacement accompanying expansion and contraction is larger in the surface direction than in the thickness direction. That is, the actuator unit 21 uses the upper one piezoelectric sheet 141 away from the pressure chamber 110 as a layer including an active portion and the lower two piezoelectric sheets 142 and 143 close to the pressure chamber 110 as inactive layers. The so-called unimorph type. As shown in FIG. 6A, since the piezoelectric sheets 141 to 143 are fixed to the upper surface of the cavity plate 122 that partitions the pressure chamber 110, the electric field application portion of the piezoelectric sheet 141 and the piezoelectric sheets 142 and 143 below the electric field application portion. If there is a difference in distortion in the plane direction between the piezoelectric sheets 141 and 143, the entire piezoelectric sheets 141 to 143 are deformed so as to be convex toward the pressure chamber 110 (unimorph deformation). As a result, pressure (discharge energy) is applied to the ink in the pressure chamber 110, and a pressure wave is generated in the pressure chamber 110. Then, the generated pressure wave propagates from the pressure chamber 110 to the nozzle 108, whereby an ink droplet is ejected from the nozzle 108.

In this embodiment, a predetermined potential is applied to the individual electrode 135 in advance, and a ground potential is once applied to the individual electrode 135 every time there is a discharge request, and then the predetermined potential is applied again at a predetermined timing. A drive signal to be applied to the individual electrode 135 is output from the driver IC 52. In this case, at the timing when the individual electrode 135 becomes the ground potential, the pressure of the ink in the pressure chamber 110 drops and the ink is sucked from the sub manifold channel 105 a into the individual ink channel 132. Thereafter, the ink pressure in the pressure chamber 110 rises at the timing when the individual electrode 135 is set to a predetermined potential again, and ink droplets are ejected from the nozzles 108. That is, a rectangular wave pulse is applied to the individual electrode 135. This pulse width is AL (Acoustic Length), which is the length of time during which the pressure wave propagates from the outlet of the sub-manifold 105a to the tip of the nozzle 108 in the pressure chamber 110, and the ink in the pressure chamber 110 is in a negative pressure state. Since both pressures are combined when reversing to the positive pressure state, ink droplets can be ejected from the nozzles 108 with a strong pressure. Note that in this embodiment, the predetermined potential is 24 V (see FIG. 7).

  The ink-jet printer 101 uses fast-drying ink, and ink droplets that have landed on the paper P are dried instantly. Thereby, the discharge period of ink droplets can be shortened, and high-speed printing is possible. On the other hand, when fast-drying ink is used, the ink in the nozzle 108 is dried and easily thickened. If the ink in the nozzle 108 is thickened, the ink ejection characteristics may deteriorate or ejection failure may occur. Therefore, in the inkjet printer 101, normal printing in which ink droplets are ejected from the nozzles 108, and non-ejection flushing that stirs the ink in the nozzles 108 by vibrating the ink meniscus formed in the openings of the nozzles 108 are performed. Done selectively.

  Specifically, the substrate 54 determines whether or not the paper P is opposed to the ink ejection surface 2 a based on a detection result of a paper detection sensor (not shown), and the paper P is in contact with the ink ejection surface 2 a of the inkjet head 1. Normal printing is performed only when facing each other, and non-ejection flushing is performed only when the paper P is not facing the ink ejection surface 2a.

  Next, the waveform of the drive signal output from the driver IC 52 will be described with reference to FIG. FIG. 7 is a waveform diagram of a drive signal that the driver IC 52 intends to output. FIG. 7A shows an example of the ejection waveform within one printing cycle, and FIG. 7B shows an example of the non-ejection flushing waveform. Here, the printing cycle is the time required for the paper P to be conveyed by a unit distance corresponding to the print resolution of the image formed on the paper P (for example, 600 dpi in the present embodiment). The driver IC 52, based on an instruction from the substrate 54, discharge waveform (first waveform) that is a waveform output when performing normal printing and flushing waveform (waveform that is output when non-ejection flushing is performed). 2nd waveform) is selectively output to each individual electrode 135. The ejection waveform includes pulses that are continuous according to the number of ink droplets ejected from the nozzle 108 within one printing cycle. The gradation of each dot constituting the image formed on the paper P is expressed by an ink ejection amount adjusted by the number of ink droplets ejected from the nozzle 108 within one printing cycle. Accordingly, there are a plurality of types of ejection waveforms depending on the number of ink droplets ejected from the nozzle 108 (ink ejection amount) within one printing cycle. In this embodiment, since the number of ink droplets ejected from the nozzle 108 within one printing cycle is 1 to 3 droplets, there are a total of three types of ejection waveforms. FIG. 7A shows an ejection waveform for ejecting three ink droplets from the nozzle 108 within one printing cycle.

  As shown in FIGS. 7A and 7B, the non-ejection flushing waveform is a series of pulses greater in number than the number of pulses in the ejection waveform. The pulse width of the non-ejection flushing waveform is shorter than the pulse width of the ejection waveform, and the period T1 of the non-ejection flushing waveform is shorter than the period T0 of the ejection waveform. Thereby, the frequency of the non-ejection flushing waveform is higher than the frequency of the ejection waveform. In this embodiment, the frequency of the ejection waveform is 60 KHz, and the frequency of the non-ejection flushing waveform is 100 KHz. Thus, since the pulse width of the non-ejection flushing waveform is shorter than the pulse width of the ejection waveform, the pulse width of the non-ejection flushing waveform is equal to or less than AL. As a result, when the drive signal having the non-ejection flushing waveform reverses the ink in the individual electrode pressure chamber 110 from the negative pressure state to the positive pressure state, the pressures of the two interfere with each other, and the ink droplets are not ejected from the nozzle 108. .

  Further, the drive voltage of the non-ejection flushing waveform to be output by the driver IC 52 is the same as the drive voltage of the ejection waveform. As described above, since the frequency of the non-ejection flushing waveform is higher than the frequency of the ejection waveform, the power that the driver IC 52 intends to consume when outputting the non-ejection flushing waveform is the driver when outputting the ejection waveform. It becomes larger than the electric power which IC52 is going to consume. Therefore, the power to be supplied when each driver IC 52 outputs a non-ejection flushing waveform to all the individual electrodes 135 is the maximum number of inks that each driver IC 52 supplies to all the individual electrodes 135 within one printing cycle. This is larger than the power to be supplied to each driver IC 52 when a discharge waveform for discharging a droplet is output. As will be described later, when non-ejection flushing is performed, the current supplied to the driver IC 52 is limited. Therefore, in the drive signal that the driver IC 52 actually outputs to the individual electrode 135, the non-ejection flushing waveform is driven. The voltage becomes lower than the drive voltage of the ejection waveform (see FIG. 9).

  Next, the power supply device 16 will be described in detail with reference to FIG. FIG. 8 is a functional block diagram of the power supply device 16. As shown in FIG. 8, the power supply device 16 supplies power to the driver IC 52 of each inkjet head 1, and includes an AC / DC converter 84 and a current limiting circuit (current limiting means) 85. . The AC / DC converter 84 converts an alternating current supplied from an external power source into a direct current. In the present embodiment, the AC / DC converter 84 converts AC 110V supplied from an external power source into DC 30V. The electric power output from the AC / DC converter 84 is output to the current limiting circuit 85.

  The current limiting circuit 85 limits the current supplied from the power supply device 16 to the driver IC 52 to be less than a predetermined upper limit current, and includes a DC / DC converter 86 and a current detection circuit 87. The DC / DC converter 86 is a switching regulator that stabilizes the electric power output from the AC / DC converter 84 at 24V DC and outputs the stabilized power. The electric power output from the DC / DC converter 86 is supplied to the driver IC 52 through the current detection resistor R1. The current detection circuit 87 detects the current output from the DC / DC converter 86 by measuring the voltage across the current detection resistor R1. Further, the current detection circuit 87 outputs a stop signal to the DC / DC converter 86 when the detected current becomes equal to or greater than a predetermined upper limit current. When a stop signal is output from the current detection circuit 87, the DC / DC converter 86 stops outputting power. When the DC / DC converter 86 stops outputting power, the current detection circuit 87 stops detecting the current exceeding the upper limit current, and stops outputting the stop signal. When the current detection circuit 87 stops outputting the stop signal, the DC / DC converter 86 starts outputting power again. Thus, the current limiting circuit 85 limits the current supplied to the driver IC 52 to less than the upper limit current by configuring a feedback circuit. Therefore, the current limiting circuit 85 also functions as an overcurrent protection device.

  Here, the upper limit current is the maximum current that the driver IC 52 intends to consume when performing normal printing, that is, each driver IC 52 ejects the maximum number of ink droplets to all the individual electrodes 135 within one printing cycle. When the discharge waveform is output, the current to be supplied to each driver IC 52 exceeds the current to be consumed by the driver IC 52 when non-ejection flushing is performed, that is, each driver IC 52 applies to all the individual electrodes 135. Thus, it is determined in a range that does not satisfy the current to be supplied when the non-ejection flushing waveform is output. In the present embodiment, the maximum current that the driver IC 52 intends to consume when performing normal printing is 1 A, and the current that the driver IC 52 attempts to consume when performing non-ejection flushing is 2 A. Therefore, the upper limit current is 1.5A is determined. The resistance value of the current detection resistor R1 is 0.1Ω. Accordingly, when the voltage across the current detection resistor R1 becomes 150 mV or more, that is, when the current output from the DC / DC converter 86 becomes 1.5 A or more, the current detection circuit 87 The stop signal is output to the converter 86. Here, when the non-ejection flushing is performed, the current to be consumed by the driver IC 52 is 2 A and the voltage is 24 V. Therefore, the load at this time is 12Ω. Therefore, if the current supplied to the driver IC 52 is limited to 1.5 A when non-ejection flushing is performed, the driving voltage of the non-ejection flushing waveform output from the driver IC 52 is 12Ω × 1.5 A = 18V.

  Next, the operation of the power supply device 16 will be described in detail with reference to FIGS. 9 and 10. FIG. 9 is a graph showing the power supply characteristics of the power supply device 16. In FIG. 9, the horizontal axis indicates the supplied current (A), and the vertical axis indicates the supplied voltage (V). FIG. 10 is a waveform diagram of drive signals actually output from the driver IC 52. 10A shows the ejection waveform within one printing cycle, and FIG. 10B shows the non-ejection flushing waveform. As shown in FIG. 9, when the power supply device 16 supplies the driver IC 52 with power less than the upper limit current 1.5A, the voltage supplied by the power supply device 16 is constant at 24V. However, when the power supply device 16 supplies power with an upper limit current of 1.5 A or more to the driver IC 52, the current supplied by the current limiting circuit 85 is limited. As described above, the voltage at this time is 18V.

  As shown in FIG. 9 and FIG. 10A, when the driver IC 52 outputs an ejection waveform to the individual electrode 135 for normal printing, the current that the driver IC 52 intends to consume is 1 A at the maximum. Therefore, the current supplied from the power supply device 16 is not limited by the current limiting circuit 85. Therefore, the drive voltage of the ejection waveform output from the driver IC 52 is constant at 24V. On the other hand, as shown in FIG. 9 and FIG. 10B, when each driver IC 52 outputs a non-ejection flushing waveform to all the individual electrodes 135 in order to perform non-ejection flushing, the driver IC 52 tries to consume. Therefore, the current limiting circuit 85 limits the current supplied by the power supply device 16 to the upper limit current 1.5A. For this reason, the drive voltage of the non-ejection flushing waveform output from the driver IC 52 is lowered to 18V. At this time, the actuator unit 21 is driven within a range where ink droplets are not ejected from the nozzle 108, and the ink meniscus formed in the opening of the nozzle 108 vibrates. Thereby, the ink in the nozzle 108 is agitated.

  As described above, according to the present embodiment described above, when each driver IC 52 tries to output a non-ejection flushing waveform to all the individual electrodes 135, the current limiting circuit 85 limits the current supplied from the power supply device 16 to the driver IC 52. Since the current is limited to 1.5 A, power saving of the ink jet printer 101 can be achieved.

  Hereinafter, various modifications according to the present embodiment will be described. In the inkjet printer 101 described above, the driver IC 52 outputs a drive signal having a discharge waveform when performing normal printing, and a non-discharge flushing waveform having a pulse width narrower (higher frequency) than the discharge waveform when performing non-discharge flushing. However, the driver IC 52 may output a drive signal having the same ejection waveform when performing normal printing and non-ejection flushing.

(First modification)
In the first modification, since a black image is formed on the entire printing area of the paper P, when ink droplets are ejected from all the nozzles 108 within one printing cycle, the second largest ink ejection amount from the nozzles 108. In other words, the driver IC 52 has a discharge waveform for discharging the second largest number of ink droplets (for example, two to three ink droplets when discharging one to three ink droplets). Output to the individual electrodes 135. When ink droplets are ejected from all the nozzles 108 within one printing cycle, the driver IC 52 generates an ejection waveform for ejecting the second largest ink ejection amount from at least one nozzle 108 to the individual electrode 135. As long as it outputs, you may comprise so that the discharge waveform of arbitrary patterns may be output to the other separate electrode 135. FIG.

  When non-ejection flushing is performed, the driver IC 52 generates an ejection waveform for ejecting the largest amount of ink from all the nozzles 108, in other words, ejecting the largest number of ink droplets. Output to the electrode 135. Accordingly, when the non-ejection flushing is performed, the power that the driver IC 52 intends to consume, that is, when each driver IC 52 outputs an ejection waveform for ejecting the largest number of ink droplets to all the individual electrodes 135 is output. Therefore, the power to be supplied to the driver IC 52 is larger than the power to be consumed by the driver IC 52 during normal printing.

  At this time, the upper limit current in the current limiting circuit 85 is determined in the vicinity of the current that the driver IC 52 intends to consume when non-ejection flushing is performed. According to this, in order to perform non-ejection flushing, when each driver IC 52 outputs an ejection waveform for ejecting the largest number of ink droplets to all the individual electrodes 135, the current limiting circuit 85 causes the power supply device 16. Is supplied to the upper limit current, and the drive voltage of the ejection waveform output from the driver IC 52 is lowered. In this way, when non-ejection flushing is performed, the drive voltage of the non-ejection flushing waveform is lowered, so that the deformation amount of the actuator unit 21 is reduced, and ink droplets are not ejected from the corresponding nozzles 108. The ink meniscus formed in the opening 108 vibrates. Thereby, the ink in the nozzle 108 is agitated.

  According to the first modification described above, the current limiting circuit 85 limits the current output from the power supply device 16 when non-ejection flushing is performed, so that power saving of the inkjet printer 101 can be achieved. In addition, the current limiting circuit 85 that functions as an overcurrent protection device generates a voltage control circuit that changes the drive voltage and a waveform for non-ejection flushing in order to change the drive voltage of the drive signal when non-ejection flushing is performed. This eliminates the need for a waveform generation circuit to reduce the cost of the inkjet printer 101.

(Second modification)
Next, a second modification will be described with reference to FIG. FIG. 11 is a plan view of the head body 2. As shown in FIG. 11, the ink discharge surface 2 a has a discharge area A and a non-discharge area B. The ejection area A is an area where the nozzles 108 facing the printing area on the maximum size paper P are arranged, in other words, an area where the nozzles 108 capable of ejecting ink droplets onto the paper P are arranged. The non-ejection area B is an area adjacent to both sides in the direction orthogonal to the transport direction of the paper P in the ejection area A, and the nozzles 108 are arranged. Further, the non-ejection area B corresponds to a further oblique side area of each actuator unit 21 located outside the longitudinal direction of the head main body 2. The hypotenuse region of the actuator unit 21 corresponding to the non-ejection region B is generated by realizing a long head while keeping the shape of each actuator unit 21 of the head body 2 the same, and is directly applied to printing on the paper P. It does not contribute. However, the manufacturing cost of the actuator unit 21 can be reduced by making the shape of all the actuator units 21 the same. Further, since the operation characteristics of the actuator units 21 are made uniform, variations in ink droplet ejection characteristics are less likely to occur. Furthermore, an individual ink flow path 132 corresponding to the oblique side area of the actuator unit 21 described above is formed in the flow path unit 9. The nozzles 108 of the individual ink flow path 132 are arranged in the non-ejection area B. The individual ink flow path 132 related to the non-ejection area B also does not directly contribute to printing on the paper P, but is formed in order to make the physical influence (rigidity) from the actuator unit 21 uniform.

  In the second modification, when normal printing is performed, ink droplets are ejected only from the nozzles 108 associated with the ejection region A, in other words, ink droplets are not ejected from the nozzles 108 associated with the non-ejection region B. In addition, the driver IC 52 outputs various ejection waveforms only to the individual electrodes 135 corresponding to the nozzles 108 in the ejection area A within one printing cycle. When non-ejection flushing is performed, ejection waveforms for ejecting the largest number of ink droplets from all the nozzles 108 related to the ejection area A and the non-ejection area B are output to all the individual electrodes 135. As a result, the power that the driver IC 52 tends to consume when non-ejection flushing is performed, that is, each driver IC 52 is the largest for all the individual electrodes 135 corresponding to the nozzles 108 in the ejection area A and the non-ejection area B. The power to be supplied when the ejection waveform for ejecting the number of ink droplets is output is the maximum power that the driver IC 52 intends to consume when performing normal printing, that is, each driver IC 52 relates only to the ejection area A. This is larger than the power to be supplied when the ejection waveform for ejecting the largest number of ink droplets to all the individual electrodes 135 corresponding to the nozzles 108 is output.

  Here, the upper limit current is determined in a range that exceeds the maximum current that the driver IC 52 intends to consume when performing normal printing and that does not satisfy the current that the driver IC 52 intends to consume when performing non-ejection flushing. Thus, in order to perform non-ejection flushing, when each driver IC 52 outputs ejection waveforms to all the individual electrodes 135 corresponding to the nozzles 108 in the ejection area A and the non-ejection area B, the current limiting circuit 85 The current supplied by the power supply device 16 is limited to the upper limit current, and the drive voltage of the ejection waveform output from the driver IC decreases. In this way, when non-ejection flushing is performed, the drive voltage of the non-ejection flushing waveform is lowered, so that the deformation amount of the actuator unit 21 is reduced, and ink droplets are not ejected from the corresponding nozzles 108. The ink meniscus formed in the opening 108 vibrates. Thereby, the ink in the nozzle 108 is agitated.

  According to the second modification described above, the current limiting circuit 58 limits the current output from the power supply device 16 when non-ejection flushing is performed, so that power saving of the inkjet printer 101 can be achieved. In addition, the current limiting circuit 85 that functions as an overcurrent protection device generates a voltage control circuit that changes the drive voltage and a waveform for non-ejection flushing in order to change the drive voltage of the drive signal when non-ejection flushing is performed. This eliminates the need for a waveform generation circuit to reduce the cost of the inkjet printer 101.

(Second Embodiment)
Next, an ink jet printer according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 12 is a functional block diagram of the power supply device 216 included in the ink jet printer according to the present embodiment. FIG. 13 is a graph showing the power supply characteristics of the power supply device 216. In FIG. 13, the horizontal axis indicates the supplied current (A), and the vertical axis indicates the supplied voltage (V). Note that the present embodiment is substantially the same in other members and devices except for the configuration of the power supply device 216 as compared to the first embodiment described above. Therefore, only the power supply device 216 will be described in detail below, and the same members and devices as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 12, the power supply device 216 supplies power to the driver IC 52 of each inkjet head 1 and includes an AC / DC converter 84 and a three-terminal regulator (current limiting means) 285. . The AC / DC converter 84 converts an alternating current supplied from an external power source into a direct current. The power output from the AC / DC converter 84 is output to the three-terminal regulator 285. The three-terminal regulator 285 stabilizes the power supply output and limits the current supplied from the power supply device 216 to the driver IC 52 to be less than a predetermined upper limit current. Therefore, the three-terminal regulator 285 also functions as an overcurrent protection device. In the present embodiment, the three-terminal regulator 285 stabilizes the power output at DC 24V. The upper limit current is determined to be 1.5A.

  As shown in FIG. 13, when the power supply device 16 supplies the driver IC 52 with power less than the upper limit current 1.5A, the voltage supplied by the power supply device 16 is constant at 24V. However, when the power supply device 16 supplies power with an upper limit current of 1.5 A or more to the driver IC 52, the current supplied by the power supply device 16 is limited by the current limiting circuit 85. In the current limiting circuit 85, once the current limitation is started, the voltage decreases exponentially as the output current decreases.

  Therefore, when the driver IC 52 outputs an ejection waveform to all the individual electrodes 135 for normal printing, the current that the driver IC 52 intends to consume is 1 A at the maximum, so that the three-terminal regulator 285 causes the power supply device 216. The current supplied by is not limited. For this reason, the drive voltage of the ejection waveform output from the driver IC 52 is constant at 24V. On the other hand, since non-ejection flushing is performed, when each driver IC 52 outputs a non-ejection flushing waveform to all the individual electrodes 135, the current that the driver IC 52 intends to consume is 2 A, so the three-terminal regulator 285 The current supplied by the power supply device 216 is limited. For this reason, the drive voltage of the non-ejection flushing waveform output from the driver IC 52 decreases (see FIG. 9). At this time, the actuator unit 21 is driven within a range where ink droplets are not ejected from the nozzle 108, and the ink meniscus formed in the opening of the nozzle 108 vibrates. Thereby, the ink in the nozzle 108 is agitated.

  As described above, according to the present embodiment described above, when each driver IC 52 attempts to output a non-ejection flushing waveform to all the individual electrodes 135, the three-terminal regulator 285 limits the current supplied from the power supply device 16 to the driver IC 52. Since the current is limited to 1.5 A, power saving of the ink jet printer can be achieved. In addition, since the inexpensive three-terminal regulator 285 is used, the cost of the ink jet printer can be reduced.

(Third embodiment)
Next, an ink jet printer according to a third embodiment of the present invention will be described with reference to FIGS. FIG. 14 is a functional block diagram of the power supply device 316 included in the ink jet printer according to the present embodiment. FIG. 15 is a graph showing characteristics of power supplied from the power supply device 316 to the driver IC 52. In FIG. 15, the horizontal axis indicates the supplied current (A), and the vertical axis indicates the supplied voltage (V). Note that the present embodiment is substantially the same in other members and devices except for the configuration of the power supply device 316 as compared with the first embodiment described above. Therefore, hereinafter, only the power supply device 316 will be described in detail, and the same members and devices as those of the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  As illustrated in FIG. 14, the power supply device 316 includes an AC / DC converter 84. The AC / DC converter 84 converts an alternating current supplied from an external power source into a direct current. The power output from the AC / DC converter 84 is output to the substrate 54 (driver IC 52) via the cable (power line) 385. The cable 385 is made of the same member as a signal line (not shown) for outputting a control signal to the driver IC 52, such as a flat flexible cable, and has an internal resistance R2. In FIG. 14, the cable 385 is illustrated as connecting the power supply device 316 and the substrate 54, but is considered to include wiring formed in the COF 50 that connects the substrate 54 and the driver IC 52. . Further, the cable 385 may be formed of a member different from a signal line for outputting a control signal to the driver IC 52. The resistance value of the internal resistor R2 is determined so that the voltage supplied to the driver IC 52 decreases when the current supplied to the driver IC 52 becomes equal to or higher than the upper limit current.

  As shown in FIG. 15, when the power supply device 316 supplies power that does not satisfy the upper limit current 1.5A to the driver IC 52, the voltage supplied to the driver IC 52 is constant at 24V. However, when the power supply device 16 supplies power with an upper limit current of 1.5 A or more to the driver IC 52, the voltage supplied to the driver IC 52 is reduced by the internal resistance R2 of the cable 385. For example, when the resistance value of the internal resistor R2 is 2Ω, the drive voltage is 4V because a current of 2A tends to flow through the cable 385 during non-ejection flushing.

  When the driver IC 52 outputs an ejection waveform to all the individual electrodes 135 for normal printing, the current that the driver IC 52 intends to consume is 1 A at the maximum, so the internal resistance R2 of the cable 385 causes the driver IC 52 to The supplied voltage does not decrease. For this reason, the drive voltage of the ejection waveform output from the driver IC 52 is constant at 24V. On the other hand, when non-ejection flushing is performed, when each driver IC 52 outputs a non-ejection flushing waveform to all the individual electrodes 135, the current that the driver IC 52 intends to consume is 2 A, so the internal resistance of the cable 385 The voltage supplied to the driver IC 52 by R2 decreases, and the drive voltage of the non-ejection flushing waveform output from the driver IC 52 decreases (see FIG. 9). At this time, the actuator unit 21 is driven within a range where ink droplets are not ejected from the nozzle 108, and the ink meniscus formed in the opening of the nozzle 108 vibrates. Thereby, the ink in the nozzle 108 is agitated.

  As described above, according to the present embodiment described above, the drive voltage of the non-ejection flushing waveform output from the driver IC 52 is lowered by the internal resistance R2 of the cable 385, and the voltage control circuit for performing non-ejection flushing and the non-ejection A waveform generation circuit for generating a waveform for flushing is not required, and deterioration of ink ejection characteristics and ejection failure can be suppressed, and the cost of the inkjet printer can be reduced.

  Further, since the cable 385 is formed of the same member as the signal line for outputting a control signal to the driver IC 52, the cost of the cable 385 can be reduced.

  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 first to third embodiments described above, the actuator unit 21 is a unimorph type piezoelectric type. However, the actuator unit 21 is an actuator that is driven by inputting a pulsed drive signal, and the pulse drive voltage is used. Other actuators may be used as long as the driving amount changes.

  In the third embodiment described above, the driver IC 52 outputs a drive signal having a discharge waveform when performing normal printing, and the pulse width is narrower (higher frequency) than the discharge waveform when performing non-discharge flushing. Although it is configured to output a drive signal having an ejection flushing waveform, the driver IC 52 performs the same ejection when performing normal printing and non-ejection flushing as shown in the first to third modifications in the first embodiment. The configuration may be such that a waveform drive signal is output.

DESCRIPTION OF SYMBOLS 1 Inkjet head 2a Ink discharge surface 6, 7 Belt roller 8 Conveyor belt 9 Flow path unit 16 Power supply device 21 Actuator unit 52 Driver IC
54 Substrate 84 AC / DC converter 85 Current limiting circuit 86 DC / DC converter 87 Current detection circuit 101 Inkjet printer 108 Nozzle 110 Pressure chamber 132 Individual ink flow path 134 Common electrode 135 Individual electrodes 141 to 143 Piezoelectric sheet 216 Power supply device 285 3 terminals Regulator 316 Power supply 385 Cable

Claims (4)

A flow path unit in which a plurality of individual ink flow paths from the common ink chamber to the nozzle via the pressure chamber are formed;
An actuator including an individual electrode associated with the pressure chamber, a ground electrode to which a reference potential is applied, and a piezoelectric layer disposed between the individual electrode and the ground electrode;
A waveform including a pulse for driving the actuator, a first waveform including a pulse for driving the actuator so that an ink droplet is ejected from the nozzle, and a pulse width smaller than the pulse of the first waveform; and, a pulse for driving the actuator to the extent that ink droplets from the nozzle is not ejected, than the first waveform pulse plurality of pulses unrealized said first waveform continuously and closely spaced than the spacing of the Waveform output means for selectively outputting a second waveform consuming a large amount of power to the individual electrodes;
An AC / DC converter supplied with power from an external power source;
When the current input from the AC / DC converter is less than the upper limit current, the current is output to the waveform output means without being limited, and when the current input from the AC / DC converter is greater than or equal to the upper limit current Has a current limiting means for limiting the current and outputting it to the waveform output means,
The upper limit current exceeds a current to be supplied when the waveform output means outputs the first waveform to all the individual electrodes, and the waveform output means applies to the individual electrodes for all the individual electrodes. Less than the current to be supplied when the second waveform is output at the same drive voltage as the pulse of the first waveform ,
The current limiting means limits and outputs a current equal to or higher than the upper limit current input from the AC / DC converter when the waveform output means outputs the second waveform to all the individual electrodes. Thus, the voltage of the electric power supplied to the waveform output means is reduced, and the drive voltage of the pulse having the second waveform is set to a voltage at which no ink droplet is ejected from the nozzle .   The first waveform has a frequency at which a current less than the upper limit current is consumed when the actuator is driven by being supplied to all the individual electrodes, and the second waveform is more than the first waveform. 2. The frequency according to claim 1, wherein the actuator has a high frequency and is supplied to all the individual electrodes, and has a frequency at which a current higher than the upper limit current is consumed when the actuator is driven. The inkjet printer described in 1. A transport device for transporting a recording medium;
A flow path unit in which a plurality of individual ink flow paths from the common ink chamber to the nozzle via the pressure chamber are formed;
An actuator including an individual electrode associated with the pressure chamber, a ground electrode to which a reference potential is applied, and a piezoelectric layer disposed between the individual electrode and the ground electrode;
When the time required for transporting 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, different amounts from the nozzles in the one printing cycle Waveform output means for selectively outputting to the individual electrodes a plurality of types of waveforms from which ink is ejected, including a plurality of waveforms that drive the actuator.
Control means for controlling the waveform output means;
An AC / DC converter supplied with power from an external power source;
When the current input from the AC / DC converter is less than the upper limit current, the current is output to the waveform output means without being limited, and when the current input from the AC / DC converter is greater than or equal to the upper limit current Has a current limiting means for limiting the current and outputting it to the waveform output means,
When the actuator drives the actuator so that ink droplets are ejected from some of the nozzles, the control means applies to a part of the individual electrodes corresponding to the part of the nozzles within one printing cycle. When controlling the actuator to output any one of the plurality of ejection waveforms and driving the actuator so that ink droplets are ejected from all the nozzles, at least one of the individual electrodes within one printing cycle And outputting a discharge waveform corresponding to an amount equal to or less than the second largest discharge amount of the plurality of discharge waveforms, and outputting any one of the plurality of discharge waveforms to the other individual electrodes. When the actuator is driven in a range in which ink droplets are not ejected from all the nozzles, all the individual electrodes are applied within one printing cycle. Serial control to output a discharge waveform corresponding to the largest amount of ink discharge among the plurality of ejection waveforms,
The upper limit current corresponds to an amount equal to or less than the second largest amount of ink ejected by the waveform output means for at least one of the individual electrodes in order to eject ink droplets from all the nozzles within the one printing cycle. The discharge waveform exceeds the current to be supplied when the discharge waveform corresponding to the largest ink discharge amount is output to the other individual electrodes , and the waveform output means Less than the current to be supplied when the ejection waveform corresponding to the largest ink ejection amount is output to the individual electrode ,
The current limiting means is inputted from the AC / DC converter when the waveform output means outputs the ejection waveform corresponding to the largest ink ejection amount to all the individual electrodes within the one printing cycle. By limiting the output current, the voltage of the power supplied to the waveform output means is reduced, and the drive voltage of the pulse of the discharge waveform is set to a voltage at which no ink droplet is discharged from the nozzle. Inkjet printer. When ink droplets are ejected from all the nozzles within the one printing cycle, the waveform output means is configured to eject the ink of an amount equal to or less than the second largest ink ejection amount to all the individual electrodes. The inkjet printer according to claim 3 , wherein a discharge waveform is output.

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