JP2011056729A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To overcome the problem that the rate of success in recovery by the empty delivering operation becomes low, and the empty recovering operation has to be repeated when an empty delivering is performed to a recording head under a condition that a meniscus tends to break and air bubbles tend to be dragged, and when the meniscus is broken. <P>SOLUTION: The recording head 34 has a configuration that an ink feeding opening 132 is arranged at the central part in the nozzle arranging direction and ink is fed to a plurality of the nozzles 104 of one row. When the empty delivering operation is performed, in the nozzle arranging direction, in an order from the nozzle 104 at the central part where the path to the ink feeding opening 132 is short to the nozzles 104 on both ends where the path to the ink feeding opening 132 is long, the empty delivering is performed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an idle ejection operation in an image forming apparatus including a recording head that ejects droplets.

  As an image forming apparatus such as a printer, a facsimile, a copying machine, a plotter, or a complex machine of these, for example, a liquid discharge recording type image forming using a recording head composed of a liquid discharge head (droplet discharge head) that discharges ink droplets. As an apparatus, an ink jet recording apparatus or the like is known. This liquid discharge recording type image forming apparatus means that ink droplets are transported from a recording head (not limited to paper, including OHP, and can be attached to ink droplets and other liquids). Yes, it is also ejected onto a recording medium or a recording medium, recording paper, recording paper, etc.) to form an image (recording, printing, printing, and printing are also used synonymously). And a serial type image forming apparatus that forms an image by ejecting liquid droplets while the recording head moves in the main scanning direction, and a line type head that forms images by ejecting liquid droplets without moving the recording head There are line type image forming apparatuses using

  In the present application, the “image forming apparatus” of the liquid discharge recording method is an apparatus that forms an image by discharging liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, or the like. In addition, “image formation” means not only giving an image having a meaning such as a character or a figure to a medium but also giving an image having no meaning such as a pattern to the medium (simply It also means that a droplet is landed on a medium). “Ink” is not limited to ink, but is used as a general term for all liquids capable of image formation, such as recording liquid, fixing processing liquid, and liquid. DNA samples, resists, pattern materials, resins and the like are also included. In addition, the “image” is not limited to a planar one, but includes an image given to a three-dimensionally formed image and an image formed by three-dimensionally modeling a solid itself.

  In addition, as an image forming apparatus including a liquid discharge head, a serial type image recording apparatus that performs recording by mounting a recording head on a carriage and moving the recording head in a main scanning direction orthogonal to a sheet feeding direction, and an abbreviation of a recording area. There is a line-type image recording apparatus using a line-type head in which a plurality of discharge ports (nozzles) for discharging droplets over the entire width are arranged.

  By the way, the liquid discharge head constituting the recording head used in the image forming apparatus performs recording by discharging liquid droplets from the discharge port (nozzle). The viscosity of the ink in the vicinity of the thin film portion such as the opening portion and the pressure vibration attenuation portion of the common liquid chamber having low air permeability and moisture permeability gradually increases due to water evaporation that progresses with time. In addition, although the ink components are uniformly dispersed, components with high specific gravity such as pigments settle down over time, and in particular, a phenomenon occurs in which the viscosity of the bottom increases in a large capacity ink reservoir such as a common liquid chamber. To do.

  When such a thickening phenomenon occurs, it is necessary to recover the state in which the thickened ink inside the nozzles can be discharged and ejected normally. Normally, ink is discharged from the nozzles by means such as cap suction as a method for recovery of discharge, but this recovery method involving the cap suction recovery operation requires a large amount of ink consumption. However, if the standing time is short and the degree of increase in viscosity is low, it can be recovered only by the empty discharge operation for discharging a droplet that does not contribute to image formation (this is referred to as “empty discharged droplet”). is there.

  In the recovery operation by the idle ejection, the leaving time region that can be recovered without the suction operation is determined depending on how the viscosity increasing ink ejection efficiency (empty ejection efficiency) can be secured.

  In the conventional idle discharge operation, the amplitude width of the idle discharge waveform is increased to drive with a waveform with a large discharge energy, or control is performed such that the idle discharge operation is periodically executed before viscosity increase occurs. Thus, it has been recovered to a state where it can be normally discharged without a suction recovery operation.

JP-A-7-290720 JP 2002-273912 A Japanese Patent Laid-Open No. 2-102066 JP 2008-290400 A

  By the way, when the idle discharge is performed simultaneously from all the nozzles communicating with the common liquid chamber, the pressure of the liquid chamber (pressurized liquid chamber, individual liquid chamber) communicating with the nozzle and the common liquid chamber is suddenly reduced. At this time, in a normal state, the meniscus will not be destroyed by the surface tension of the meniscus formed on the nozzle, even if the pressure fluctuates within an allowable range with the pressurized liquid chamber or the common liquid chamber.

  However, the critical liquid chamber pressure value at which the meniscus formed in the nozzle is destroyed due to an increase in the negative pressure in the pressurized liquid chamber and the common liquid chamber causes the meniscus to vibrate more than when the meniscus is stationary. The case shrinks. When the meniscus is destroyed by the negative pressure, air bubbles enter the pressurized liquid chamber and normal ejection cannot be performed. And in order to recover the non-ejection of the nozzle due to the mixing of bubbles, unless the bubbles are discharged out of the pressurized liquid chamber by the cap suction operation, the nozzle cannot be restored to a normal discharge state.

  Furthermore, moisture evaporation that occurs at the opening of the nozzle or the like when left unattended causes a thickening of the ink in the vicinity of the nozzle or a film in which the solid component of the ink is deposited on the nozzle edge and the meniscus surface formed on the nozzle. Is generated. When the volume of the pressurized liquid chamber communicating with the nozzle is changed by the pressure generating means, the nozzle edge and the meniscus formed on the nozzle are greatly displaced, and the solid component deposited on the nozzle edge and the meniscus surface formed on the nozzle moves. Or peel off. The limit liquid chamber pressure value at which the meniscus at the negative pressure of the pressurized liquid chamber or the common liquid chamber is destroyed by the movement or separation of the solid component is further reduced.

  Then, the ink existing in the flow path such as the pressurized liquid chamber and the common liquid chamber flows due to the idle discharge from the nozzle, but the fluid resistance value when the ink flows increases as the ink viscosity increases. When the fluid resistance value is large, it is difficult to supply ink to the pressurized liquid chamber and the common liquid chamber, and the negative pressure in the pressurized liquid chamber and the common liquid chamber is easily increased when the nozzle is idlely discharged.

  Also, past operation history such as down (impossible to discharge), bubble entrainment, refilling of ink, use of ink with a high amount of dissolved gas, and fluctuations in the leaving environment may cause bubbles in the flow path. Always occurs. If there is ink flow, bubbles remaining in the flow path gradually dissolve and shrink in ink with a low gas dissolved amount, or the bubbles move to a place that does not interfere with ink flow, but there is no ink flow when left standing. The gas dissolved amount of the ink in the liquid chamber increases with the standing time, and bubbles move or stay in a place where the ink flow is hindered. If air bubbles are present at a location that prevents ink flow, the fluid resistance value at that location increases, the amount of ink supplied during idle ejection from the nozzles decreases, and the negative pressure in the pressurized liquid chamber and common liquid chamber tends to increase. It becomes a state.

  That is, the meniscus is easily broken due to vibration of the meniscus, movement of the thickened ink and solid components near the nozzle, and peeling, and increase in fluid resistance due to ink thickening and movement of bubbles in the flow path due to standing. Since the negative pressure in the pressurized liquid chamber and common liquid chamber is likely to increase due to the occurrence, the meniscus is more likely to be destroyed. It has become.

  As described above, when the meniscus is easily broken and the idle ejection is performed on the recording head in which bubbles are easily involved, if the meniscus is destroyed, the recovery success rate by the idle ejection operation is reduced, and the idle ejection is performed. There is a problem that the operation must be repeated.

  The present invention has been made in view of the above problems, and it is an object of the present invention to make it difficult for a meniscus formed on a nozzle to be destroyed and to improve recovery efficiency by an idle discharge operation.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A plurality of nozzles for discharging droplets; a liquid chamber in which each nozzle communicates; a common liquid chamber for supplying a liquid to each liquid chamber; a liquid supply port for supplying the liquid to the common liquid chamber; and the liquid chamber A pressure generating means for generating pressure to pressurize the liquid, and a recording head,
Empty discharge control means for performing an empty discharge operation for discharging empty discharge droplets that do not contribute to image formation from each nozzle of the recording head, and
The idle discharge control unit is configured to perform the idle discharge operation in the order of a nozzle having a short path to the liquid supply port and a nozzle having a long path to the liquid supply port.

An image forming apparatus according to the present invention includes:
A plurality of nozzles for discharging droplets; a liquid chamber in which each nozzle communicates; a common liquid chamber for supplying a liquid to each liquid chamber; a liquid supply port for supplying the liquid to the common liquid chamber; and the liquid chamber A pressure generating means for generating pressure to pressurize the liquid, and a recording head,
Empty discharge control means for performing an empty discharge operation for discharging empty discharge droplets that do not contribute to image formation from each nozzle of the recording head, and
The idle discharge control unit is configured to perform the idle discharge operation in the order of a nozzle having a small fluid resistance value in the path to the liquid supply port and a nozzle having a large fluid resistance value in the path to the liquid supply port.

An image forming apparatus according to the present invention includes:
A plurality of nozzles for discharging droplets; a liquid chamber in which each nozzle communicates; a common liquid chamber for supplying a liquid to each liquid chamber; a liquid supply port for supplying the liquid to the common liquid chamber; and the liquid chamber A pressure generating means for generating pressure to pressurize the liquid, and a recording head,
Empty discharge control means for performing an empty discharge operation for discharging empty discharge droplets that do not contribute to image formation from each nozzle of the recording head,
The idle discharge control unit is configured to perform the idle discharge operation in the order of a nozzle group having a short path to the liquid supply port and a nozzle group having a long path to the liquid supply port.

  Here, the idle discharge control means causes the idle discharge operation to be performed for each nozzle group composed of a plurality of adjacent nozzles at the beginning of the idle discharge operation, and idle discharge from all the nozzles at the beginning of the idle discharge operation. It can be configured not to be performed.

  Further, the idle discharge control means can be configured to cause idle discharge simultaneously from all the nozzles in the later stage of the idle discharge operation.

The pressure generating means is a piezoelectric element,
The idle ejection drive waveform for driving the piezoelectric element by the idle ejection operation includes a meniscus pull-in period for displacing the piezoelectric element in the direction of expanding the volume of the liquid chamber, and a stop for stopping the displacement of the piezoelectric element for a certain period of time. A plurality of pulse groups including one or a plurality of pulses having a period and a meniscus extrusion period for displacing the piezoelectric element in a direction to reduce the volume of the liquid chamber,
The pulse continuation time from the start of the meniscus pull-in of the pulse of the pulse group to the end of meniscus push-out at the initial start of the idle discharge operation is the start of the meniscus pull-in of the pulse of the pulse group near the end of the idle discharge operation. To the end time of the meniscus extrusion to the end of the pulse duration.

  In this case, the pulse duration from the meniscus drawing start time of the pulse group to the meniscus push-out end time in the initial stage of the idle discharge operation is close to the end of the idle discharge operation. It can be configured to be shorter by 4 to 20% of the Helmholtz resonance period of the liquid chamber than the pulse duration from the drawing start time to the meniscus pushing end time.

The pressure generating means is a piezoelectric element,
In the idle ejection driving waveform for driving the piezoelectric element by the idle ejection operation, the piezoelectric element is displaced in the direction of expanding the volume of the liquid chamber, the meniscus pull-in period, and the stop for stopping the displacement of the piezoelectric element for a certain period of time. A plurality of pulse groups including a plurality of pulses having a period and a meniscus extrusion period for displacing the piezoelectric element in a direction to reduce the volume of the liquid chamber,
The pulse interval of the pulse group at the beginning of the idle ejection operation may be shorter than the pulse interval of the pulse group near the end of the idle ejection operation.

  In this case, the pulse interval of the pulse group in the initial stage of the idle discharge operation is 4% of the Helmholtz resonance period of the liquid chamber, rather than the pulse interval of the pulse group near the end of the idle discharge operation. It can be configured that the pulse interval is shorter by 20% or less.

  In addition, at the beginning of the idle discharge operation, the volume of the liquid chamber can be minimized with respect to the pressure generating means.

The pressure generating means is a piezoelectric element,
In the idle ejection driving waveform for driving the piezoelectric element by the idle ejection operation, the piezoelectric element is driven by a pulse group consisting of a plurality of pulses repeated at a cycle interval longer than the liquid supply cycle of the flow path communicating with the nozzle. Including a continuous discharge period
In the interval between the continuous discharge periods, the piezoelectric element is displaced from the state in which the volume of the liquid chamber is most reduced to the state in which it is most expanded, is stopped for a certain period in the expanded state, and is further displaced in a state of being further reduced. It can be configured to have a pulse.

  In this case, in the maximum displacement pulse, the meniscus pull-in displacement time for displacing the liquid chamber volume from the most contracted state to the most expanded state after the end of the continuous discharge period is longer than the Helmholtz resonance period of the liquid chamber. It can be set as this.

  In the maximum displacement pulse, after the continuous discharge period is finished, the liquid chamber volume is displaced from the most contracted state to the most expanded state, stopped for a certain period, and then the liquid chamber volume is reduced most again. The meniscus push-out displacement time that is displaced in a short time can be configured to be shorter than the Helmholtz resonance period of the liquid chamber.

  In the maximum displacement pulse, after the continuous discharge period ends, the liquid chamber volume is displaced from the most contracted state to the most expanded state, and again is displaced to the state in which the liquid chamber volume is most contracted again. The displacement stop time for stopping the displacement for a certain period of time can be configured to be 1/2 or more of the liquid supply cycle of the flow path communicating with the nozzle.

  In addition, after the continuous discharge period ends, the application of the maximum displacement pulse can be started after a time equal to or longer than the liquid supply cycle of the nozzle has elapsed.

  In addition, after the application of the maximum displacement pulse is completed, the next continuous discharge period can be started after a time equal to or longer than the liquid supply cycle of the nozzle has elapsed.

  Further, the amount of droplets discharged per unit time from the nozzles at the beginning of the idle discharge operation may be smaller than the amount of droplets discharged per unit time from the nozzles near the end of the idle discharge operation. .

  Further, the discharge energy of the pressure generating means may be configured to be larger at the beginning of the idle discharge operation than near the end of the idle discharge operation.

  Further, the idle ejection operation may be configured to eject idle ejection droplets toward the inside of the cap member in a state where the nozzle surface of the recording head is capped with the cap member.

  According to the image forming apparatus of the present invention, the idle ejection operation is performed in the order of the nozzle having the short path to the liquid supply port to the nozzle having the long path to the liquid supply port. Therefore, the pressure drop in the common liquid chamber is small, the meniscus is not easily destroyed, and the recovery efficiency (recovery success rate) by the idle discharge operation can be improved.

  According to the image forming apparatus of the present invention, the idle discharge operation is performed in the order of the nozzle having the small fluid resistance value in the path to the liquid supply port and the nozzle having the large fluid resistance value in the path to the liquid supply port. The number of nozzles that perform idle discharge at a time is small, the pressure drop in the common liquid chamber is small, and the meniscus is less likely to be destroyed, and the recovery efficiency (recovery success rate) by the empty discharge operation can be improved.

  According to the image forming apparatus of the present invention, the idle ejection operation is performed in the order of the nozzle group having a short path to the liquid supply port and the nozzle group having the long path to the liquid supply port. The number of nozzles is small, the pressure drop in the common liquid chamber is small, the meniscus is less likely to be destroyed, and the recovery efficiency (recovery success rate) by the idle discharge operation can be improved.

1 is a schematic side view illustrating an overall configuration of a mechanism unit of an image forming apparatus according to the present invention. It is principal part plane explanatory drawing of the mechanism part. FIG. 4 is a cross-sectional explanatory view in the longitudinal direction of the liquid chamber showing an example of a liquid discharge head constituting the recording head of the image forming apparatus. FIG. 6 is a cross-sectional explanatory view of the liquid discharge head in the lateral direction of the liquid chamber. FIG. 2 is a block explanatory diagram illustrating an overview of a control unit of the image forming apparatus. FIG. 3 is a block explanatory diagram illustrating an example of a print control unit and a head driver of the control unit. FIG. 2 is a schematic explanatory diagram of a recording head for explaining the first embodiment of the present invention. FIG. 6 is a schematic explanatory view for explaining another example of the recording head. FIG. 6 is a schematic explanatory view for explaining still another example of the recording head. It is explanatory drawing with which it uses for description of the example of the recording head from which fluid resistance values differ similarly. It is explanatory drawing with which it uses for description of the idle discharge drive waveform in 2nd Embodiment of this invention. FIG. 12 is an enlarged explanatory diagram of one pulse in FIG. 11. It is explanatory drawing with which it uses for description of the idle discharge drive waveform in 3rd Embodiment of this invention. It is explanatory drawing with which it uses for description of the idle discharge drive waveform in 4th Embodiment of this invention. FIG. 15 is an enlarged explanatory diagram for explaining the maximum displacement pulse of FIG. 14. It is explanatory drawing with which it uses for description of the idle discharge drive waveform in 5th Embodiment of this invention. It is explanatory drawing with which it uses for description of the idle discharge drive waveform in 6th Embodiment of this invention. It is explanatory drawing with which it uses for description of empty discharge in the cap of a capping state. It is explanatory drawing with which it uses for description of empty discharge in a cap of a capping state similarly.

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an example of an image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is an explanatory side view for explaining the overall configuration of the image forming apparatus, and FIG. 2 is an explanatory plan view of a main part of the apparatus.
This image forming apparatus is a serial type ink jet recording apparatus, and a carriage 33 is slidable in a main scanning direction by main and sub guide rods 31 and 32 which are guide members horizontally mounted on the left and right side plates 21A and 21B of the apparatus main body 1. It is held and moved and scanned in the direction indicated by the arrow (carriage main scanning direction) in FIG.

  The carriage 33 is provided with recording heads 34a and 34b composed of liquid ejection heads for ejecting ink droplets of yellow (Y), cyan (C), magenta (M), and black (K). The “recording head 34” is arranged in a sub-scanning direction orthogonal to the main scanning direction, and the ink droplet ejection direction is directed downward.

  Each of the recording heads 34 has two nozzle rows. One nozzle row of the recording head 34a has black (K) droplets, the other nozzle row has cyan (C) droplets, and the recording head 34b has one nozzle row. One nozzle row ejects magenta (M) droplets, and the other nozzle row ejects yellow (Y) droplets. As the recording head 34, a recording head having a nozzle row of each color in which a plurality of nozzles are arranged on one nozzle surface can be used.

  Further, the sub tanks 35a and 35b, which are sub tanks as the second ink supply unit for supplying ink of each color corresponding to the nozzle row of the recording head 34, are referred to as the “sub tank 35” when they are not distinguished. ) Is installed. In the sub tank 35, ink cartridges (main tanks) 10y, 10m, 10c, and 10k of various colors that are detachably attached to the cartridge loading unit 4 are supplied from the ink supply tubes 36 of the respective colors by the supply pump unit 24. The recording liquid is replenished and supplied.

  On the other hand, as a paper feeding unit for feeding the papers 42 stacked on the paper stacking unit (pressure plate) 41 of the paper feeding tray 2, a half-moon roller (feeding) that separates and feeds the papers 42 one by one from the paper stacking unit 41. A separation pad 44 made of a material having a large friction coefficient is provided facing the paper roller 43) and the paper feed roller 43, and the separation pad 44 is urged toward the paper feed roller 43 side.

  In order to feed the paper 42 fed from the paper feeding unit to the lower side of the recording head 34, a guide member 45 for guiding the paper 42, a counter roller 46, a transport guide member 47, and a tip pressure roller. And a holding belt 48 which is a conveying means for electrostatically attracting the fed paper 42 and conveying it at a position facing the recording head 34.

  The transport belt 51 is an endless belt, and is configured to wrap around the transport roller 52 and the tension roller 53 and circulate in the belt transport direction (sub-scanning direction). Further, a charging roller 56 that is a charging unit for charging the surface of the transport belt 51 is provided. The charging roller 56 is disposed so as to come into contact with the surface layer of the transport belt 51 and to rotate following the rotation of the transport belt 51. The transport belt 51 rotates in the belt transport direction of FIG. 2 when the transport roller 52 is rotationally driven through timing by a sub-scanning motor (not shown).

  Further, as a paper discharge unit for discharging the paper 42 recorded by the recording head 34, a separation claw 61 for separating the paper 42 from the conveying belt 51, a paper discharge roller 62, and a spur 63 that is a paper discharge roller. And a paper discharge tray 3 below the paper discharge roller 62.

  A duplex unit 71 is detachably mounted on the back surface of the apparatus body 1. The duplex unit 71 takes in the paper 42 returned by the reverse rotation of the conveyance belt 51, reverses it, and feeds it again between the counter roller 46 and the conveyance belt 51. The upper surface of the duplex unit 71 is a manual feed tray 72.

  Further, a maintenance / recovery mechanism 81 for maintaining and recovering the nozzle state of the recording head 34 is disposed in the non-printing area on one side of the carriage 33 in the scanning direction. The maintenance / recovery mechanism 81 includes cap members (hereinafter referred to as “caps”) 82a and 82b (hereinafter referred to as “caps 82” when not distinguished from each other) for capping the nozzle surfaces of the recording head 34, and nozzle surfaces. A wiper member (wiper blade) 83 for wiping the recording medium, an empty discharge receiver 84 for receiving liquid droplets when performing empty discharge for discharging liquid droplets that do not contribute to recording in order to discharge the thickened recording liquid, and a carriage And a carriage lock 87 for locking 33. A waste liquid tank 100 for storing waste liquid generated by the maintenance recovery operation is mounted on the lower side of the head recovery mechanism 81 in a replaceable manner with respect to the apparatus main body.

  Further, in the non-printing area on the other side of the carriage 33 in the scanning direction, there is an empty space for receiving liquid droplets when performing empty discharge for discharging liquid droplets that do not contribute to recording in order to discharge the recording liquid thickened during recording or the like. A discharge receiver 88 is disposed, and the idle discharge receiver 88 includes an opening 89 along the nozzle row direction of the recording head 34.

  In this image forming apparatus configured as described above, the sheets 42 are separated and fed one by one from the sheet feed tray 2, and the sheet 42 fed substantially vertically upward is guided by the guide 45, and includes the transport belt 51 and the counter. It is sandwiched between the rollers 46 and conveyed, and the leading end is guided by the conveying guide 37 and pressed against the conveying belt 51 by the leading end pressing roller 49, and the conveying direction is changed by approximately 90 °.

  At this time, a voltage is applied to the charging roller 56 so that a positive output and a negative output are alternately repeated, and the conveying belt 51 is charged with an alternating charging voltage pattern, and the sheet 42 is placed on the charged conveying belt 51. When fed, the paper 42 is attracted to the transport belt 51, and the paper 42 is transported in the sub-scanning direction by the circular movement of the transport belt 51.

  Therefore, by driving the recording head 34 according to the image signal while moving the carriage 33, ink droplets are ejected onto the stopped paper 42 to record one line, and after the paper 42 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 42 has reached the recording area, the recording operation is finished and the paper 42 is discharged onto the paper discharge tray 3.

  When performing the maintenance and recovery of the nozzles of the recording head 34, the nozzle 33 performs the suction from the nozzles by moving the carriage 33 to a position facing the maintenance and recovery mechanism 81 which is the home position and performing capping by the cap member 82. By performing a maintenance and recovery operation such as an empty discharge operation for discharging droplets that do not contribute to image formation, it is possible to perform image formation by stable droplet discharge.

  Next, an example of the liquid discharge head constituting the recording head 34 will be described with reference to FIGS. 3 is a cross-sectional explanatory diagram along the longitudinal direction of the liquid chamber of the head, and FIG. 4 is a cross-sectional explanatory diagram of the head along the lateral direction of the liquid chamber (nozzle arrangement direction).

  The liquid discharge head is formed by bonding and laminating a flow path plate 101, a vibration plate 102 bonded to the lower surface of the flow path plate 101, and a nozzle plate 103 bonded to the upper surface of the flow path plate 101. Ink is supplied to the nozzle communication path 105, which is a flow path through which the nozzle 104 that discharges droplets (ink droplets) communicates, the pressurized liquid chamber 106, which is a pressure generation chamber, and the liquid chamber 106 through a fluid resistance portion (supply path) 107. For example, an ink supply port 109 communicating with the common liquid chamber 108 is formed.

  Also, two (as shown in FIG. 3, only one row) stacked piezoelectric elements as electromechanical conversion elements that are pressure generating means (actuator means) for deforming the diaphragm 102 to pressurize the ink in the liquid chamber 106. A member 121 and a base substrate 122 to which the piezoelectric member 121 is bonded and fixed are provided. A plurality of piezoelectric element columns 121A and 121B are formed in the piezoelectric member 121 by forming grooves by slit processing that is not divided. In this example, the piezoelectric element column 121A is a driving piezoelectric element column that applies a driving waveform, and the piezoelectric element column 121B is a non-driving piezoelectric element column that does not apply a driving waveform. Further, an FPC cable 126 equipped with a drive circuit (drive IC) (not shown) is connected to the drive piezoelectric element column 121A of the piezoelectric member 121.

  The peripheral edge of the diaphragm 102 is joined to the frame member 130, and the frame member 130 serves as a through-hole 131 and a common liquid chamber 108 that house an actuator unit composed of the piezoelectric member 121 and the base substrate 122. A recess and an ink supply hole 132 which is a liquid supply port for supplying ink from the outside to the common liquid chamber 108 are formed.

  Here, the flow path plate 101 is formed by, for example, subjecting the single crystal silicon substrate having a crystal plane orientation (110) to anisotropic etching using an alkaline etching solution such as an aqueous potassium hydroxide solution (KOH), so that the nozzle communication path 105, Although a recess or a hole serving as the liquid chamber 106 is formed, the invention is not limited to a single crystal silicon substrate, and other stainless steel substrates, photosensitive resins, and the like can also be used.

  The vibration plate 102 is formed from a nickel metal plate, and is manufactured by, for example, an electroforming method (electroforming method). Alternatively, a metal plate or a joining member between a metal and a resin plate may be used. it can. The piezoelectric element columns 121 </ b> A and 121 </ b> B of the piezoelectric member 121 are bonded to the diaphragm 102 with an adhesive, and the frame member 130 is further bonded with an adhesive.

  The nozzle plate 103 forms a nozzle 104 having a diameter of 10 to 30 μm corresponding to each liquid chamber 106 and is bonded to the flow path plate 101 with an adhesive. The nozzle plate 103 is formed by forming a water repellent layer on the outermost surface of a nozzle forming member made of a metal member via a required layer.

  The piezoelectric member 121 is a stacked piezoelectric element (here, PZT) in which piezoelectric materials 151 and internal electrodes 152 are alternately stacked. An individual electrode 153 and a common electrode 154 are connected to each internal electrode 152 drawn out to different end faces of the piezoelectric member 121. In this embodiment, the ink in the liquid chamber 106 is pressurized using the displacement in the d33 direction as the piezoelectric direction of the piezoelectric member 121. However, the pressure in the d31 direction is used as the piezoelectric direction of the piezoelectric member 121. The ink in the liquid chamber 106 may be pressurized.

  In the liquid discharge head configured in this way, for example, the drive piezoelectric element column 121A contracts by lowering the voltage applied to the piezoelectric element 121 from the reference potential Ve, the diaphragm 102 is lowered, and the volume of the liquid chamber 106 is reduced. By expanding, the ink flows into the liquid chamber 106, and then the voltage applied to the driving piezoelectric element column 121A is increased to extend the driving piezoelectric element column 121A in the stacking direction, and the diaphragm 102 is deformed in the nozzle 104 direction. By contracting the volume of the liquid chamber 106, the ink in the liquid chamber 106 is pressurized, and ink droplets are ejected (jetted) from the nozzle 104.

  Then, by returning the voltage applied to the drive piezoelectric element column 121A to the reference potential, the diaphragm 102 is restored to the initial position, and the liquid chamber 106 expands to generate a negative pressure. At this time, from the common liquid chamber 108, The liquid chamber 106 is filled with ink. Therefore, after the vibration of the meniscus surface of the nozzle 104 is attenuated and stabilized, the operation proceeds to the next droplet discharge.

  Note that the driving method of the head is not limited to the above example (drawing-pushing), and striking or pushing can be performed depending on the direction of the drive waveform.

Next, an outline of the control unit of the image forming apparatus will be described with reference to FIG. In addition, the figure is a block explanatory drawing of the control part.
The control unit 500 includes a CPU 511 that also functions as a unit for controlling the idle ejection operation according to the present invention, which controls the entire apparatus, a ROM 502 that stores programs executed by the CPU 511 and other fixed data, and image data. RAM 503 for temporary storage, rewritable non-volatile memory 504 for holding data while the apparatus is powered off, image processing for performing various signal processing and rearrangement on image data, and other entire apparatus And an ASIC 505 for processing input / output signals for control.

  Further, a print control unit 508 including a data transfer unit for driving and controlling the recording head 34 and a driving signal generating unit, a head driver (driver IC) 509 for driving the recording head 34 provided on the carriage 33 side, Motor drive for driving a main scanning motor 554 that moves and scans the carriage 33, a sub-scanning motor 555 that moves the conveyor belt 51 in a circular motion, and a maintenance and recovery motor 556 that moves the cap 82 and the wiper member 83 of the maintenance and recovery mechanism 81 A unit 510, an AC bias supply unit 511 for supplying an AC bias to the charging roller 56, and the like.

  The control unit 500 is connected to an operation panel 514 for inputting and displaying information necessary for the apparatus.

  The control unit 500 has an I / F 506 for transmitting and receiving data and signals to and from the host side, an information processing device such as a personal computer, an image reading device such as an image scanner, an imaging device such as a digital camera, and the like. From the host 600 side via the cable or network via the I / F 506.

  The CPU 501 of the control unit 500 reads and analyzes the print data in the reception buffer included in the I / F 506, performs necessary image processing, data rearrangement processing, and the like in the ASIC 505, and prints the image data. The data is transferred from the unit 508 to the head driver 509. Note that generation of dot pattern data for image output is performed by the printer driver 601 on the host 600 side.

  The print control unit 508 transfers the above-described image data as serial data, and outputs a transfer clock, a latch signal, a control signal, and the like necessary for transferring the image data and confirming the transfer to the head driver 509. Including a D / A converter for D / A converting D / A conversion of drive pulse pattern data stored in the ROM, a voltage signal amplifier, a current amplifier, and the like, and a drive signal or a plurality of drive pulses Is output to the head driver 509.

  The head driver 509 selectively selects droplets of the recording head 7 as drive pulses constituting a drive signal given from the print control unit 508 based on image data corresponding to one line of the recording head 34 inputted serially. The recording head 34 is driven by applying it to a piezoelectric element as pressure generating means for generating energy to be discharged. At this time, by selecting a driving pulse constituting the driving signal, for example, dots having different sizes such as a large droplet, a medium droplet, and a small droplet can be sorted.

  The I / O unit 513 acquires information from various sensor groups 515 mounted on the apparatus, extracts information necessary for controlling the printer, and print control unit 508, motor control unit 510, AC bias supply unit Used to control 511. The sensor group 515 includes an optical sensor for detecting the position of the paper, a thermistor for monitoring the temperature in the machine, a sensor for monitoring the voltage of the charging belt, an interlock switch for detecting opening and closing of the cover, and the like. The I / O unit 513 can process various sensor information.

Next, an example of the print control unit 508 and the head driver 509 will be described with reference to FIG.
The print control unit 508 generates and outputs a drive waveform (common drive waveform) composed of a plurality of drive pulses (drive signals) within one print cycle during image formation, and within one blank discharge cycle during idle discharge operation. A drive waveform generation unit 701 that generates and outputs a drive waveform (common drive waveform) composed of a plurality of drive pulses (drive signals), and 2-bit image data (tone signals 0 and 1) corresponding to the print image A data transfer unit 702 that outputs a clock signal, a latch signal (LAT), and droplet control signals M0 to M3, and an idle ejection drive waveform generation unit 703 that generates and outputs an idle ejection drive waveform.

  The droplet control signal is a 2-bit signal that instructs each droplet to open and close an analog switch 715, which will be described later, of the head driver 209. The droplet control signal is a waveform to be selected according to the printing cycle of the common drive waveform. State transition is made to level (ON), and state transition is made to L level (OFF) when not selected.

  The head driver 509 receives a transfer clock (shift clock) from the data transfer unit 702 and serial image data (gradation data: 2 bits / 1 channel (1 nozzle)), and register values of the shift register 711. Is latched by a latch signal, a decoder 713 that decodes gradation data and control signals M0 to M3 and outputs the result, and a logic level voltage signal of the decoder 713 is a level at which the analog switch 715 can operate. A level shifter 714 that performs level conversion to an analog output, and an analog switch 716 that is turned on / off (opened / closed) by an output of a decoder 713 provided via the level shifter 714.

  The analog switch 716 is connected to the selection electrode (individual electrode) 154 of each piezoelectric element 121, and the common drive waveform from the drive waveform generation unit 701 is input thereto. Accordingly, when the analog switch 715 is turned on in accordance with the result of decoding the serially transferred image data (gradation data) and the control signals MN0 to MN3 by the decoder 713, a required drive signal constituting the common drive waveform is obtained. Passing (selected) is applied to the piezoelectric element 121.

  The idle ejection drive waveform generation unit 703 generates an idle ejection drive waveform and outputs it to the analog switch 716 when performing the idle ejection operation. Note that the common drive waveform from the drive waveform generation unit 701 and the idle ejection drive waveform from the idle ejection drive waveform generation unit 703 are selectively generated or selectively input to the analog switch 716.

Next, a different example of the first embodiment of the present invention will be described with reference to FIG. FIG. 7 is a schematic cross-sectional view of a main part in the liquid chamber arrangement direction of the recording head 34 for explaining the embodiment.
Here, the recording head 34 is configured such that an ink supply port (liquid supply port) 132 is disposed at the center in the liquid chamber arrangement direction (nozzle arrangement direction), and ink is supplied to a plurality of nozzles 104 for one row. It is said. In FIG. 8, the liquid chamber 106 is not shown.

  First, in the first example, when performing the idle ejection operation, the idle ejection is performed in the order of the nozzle 104 having the short path from the ink supply port 132 to the nozzle 104 having the long path from the ink supply port 132 in the nozzle arrangement direction. In FIG. 8, in the nozzle arrangement direction, the idle ejection is performed from the central nozzle 104 to the nozzles 104 at both ends in order. Such idle ejection control can be performed by selectively sequentially turning on the analog switch 715 that selects the idle ejection drive waveform according to data from the data transfer unit 702.

  In the second example, idle ejection is performed in the order of nozzles having a small fluid resistance value in the path from the ink supply port 132 to nozzles having a large fluid resistance value in the path from the liquid supply port. Such idle ejection control can also be performed by selectively sequentially turning on the analog switch 715 for selecting the idle ejection driving waveform according to the data from the data transfer unit 702.

  In the third example, idle ejection is performed in units of nozzle groups in the order of a nozzle group including a plurality of nozzles 103 having a short path to the ink supply port 132 and a nozzle group including a plurality of nozzles 103 having a long path to the ink supply port 132. Let it be done. Such idle ejection control can also be performed by sequentially turning on the analog switch 715 that selects the idle ejection drive waveform corresponding to the nozzle group that selectively ejects idle according to the data from the data transfer unit 702. .

  By performing such idle discharge control, the degree of pressure drop in the common liquid chamber 108 can be reduced, and the meniscus formed in the nozzle 104 can be prevented from being destroyed.

  Further, along with the ejection of the empty ejection droplets from the nozzle 104, a fresh ink passage is formed in the flow path from the ink supply port 132 to the ejection nozzle 103, and in the common liquid chamber 108 with the adjacent nozzle 103 or nozzle group. The distance to the path of the formed fresh ink is shortened, and fresh ink is easily supplied to the nozzle or nozzle group adjacent to the ejection nozzle.

  That is, the idle ejection operation is started from a nozzle or a nozzle group in which the fresh ink is most easily supplied, the path is close to the ink supply port 132, or the fluid resistance value of the flow path is low.

  At this time, it is preferable not to perform the idle discharge from all the nozzles but to perform the idle discharge with the number of nozzles of about 1 to 20% to reduce the degree of pressure drop in the common liquid chamber 108 due to the discharge. . As a result, fresh ink is gradually attracted from the ink supply port 132, and a path for fresh ink is formed in the flow path from the ink supply port 132 to the nozzle 103. Along with this, idle discharge of the nozzle or nozzle group adjacent to the discharge nozzle is started, and the number of discharge nozzles is gradually increased. As the number of ejection nozzles increases, the stirring of the fresh ink and the thickened ink by the ink flow is promoted in the common liquid chamber 108, and when driving the nozzle 104 far from the ink supply port 132 or having a large fluid resistance value in the path In the state where the viscosity of the thickened ink at the end of the nozzle arrangement direction staying in the common liquid chamber 108 is slightly lowered, the ink moves to the pressurized liquid chamber 106 of the nozzle 104 at the end, and is moved outside the nozzle by the idle discharge operation. Discharged.

  In this manner, as in the first example, the idle discharge operation is performed in the order of the nozzle having the short path to the liquid supply port and the nozzle having the long path to the liquid supply port, thereby performing the idle discharge at a time. The number of nozzles is small, the pressure drop in the common liquid chamber is small, the meniscus is less likely to be destroyed, and the recovery efficiency (recovery success rate) by the idle discharge operation can be improved.

  Since fresh ink that is not thickened is supplied to the ink supply port, the nozzle that can reach the fresh ink supplied from the ink supply port through the shortest path succeeds in recovery by idle ejection. The higher the rate and the longer the path through which fresh ink is supplied, the lower the recovery success rate by idle ejection. That is, the ink flow in the flow path can be secured with a high success rate by performing the idle discharge from the nozzle with the shortest path of the flow path from the ink supply port.

  In addition, thickened ink is difficult to mix due to the difference in specific gravity with fresh ink that is not thickened, but the flow between the ink supply port and the discharge nozzle is reduced by ink discharge from a nozzle that has a high recovery success rate due to idle discharge. A fresh ink existing area is secured between the roads. As a result, the distance of the path required for fresh ink to reach the nozzle adjacent to the discharge nozzle is remarkably shortened, and the recovery success rate by the idle discharge of the adjacent nozzle is improved.

  In this way, the success rate of idle ejection is dramatically increased by gradually performing idle ejection from adjacent nozzles and increasing the number of nozzles that can normally eject while gradually expanding the area where fresh ink exists. It becomes possible.

  In addition, the farther the flow path from the ink supply port, the greater the amount of thickened ink that must be ejected before the fresh ink reaches the nozzle. Increasing the ink increases the amount of ink that cannot be discharged normally and overflows in the vicinity of the nozzle, or the discharge energy is too weak and the surface tension of the droplet and the meniscus causes the droplet to adhere to the vicinity of the nozzle by pulling back the discharge droplet. Discharge abnormality and discharge risk are integrated, and the recovery success rate of idle discharge decreases. These risks tend to ensure normal ejection and reduce the risk as the viscosity increases.

  Therefore, it is possible to improve the recovery success rate of idle discharge by promoting idle convection and diffusion while reducing the increase in ink viscosity, rather than continuing the discharge in a high viscosity state. Is possible. Although the thickened ink is difficult to mix due to the difference in specific gravity with the fresh ink that has not been thickened, if the ink is ejected from a nozzle with a high recovery success rate and ink flow occurs in the flow path, the thickened ink And the agitation of fresh ink is promoted, and the discharge amount of ink with a high degree of increase in the viscosity of the discharge ink from the nozzle far from the ink supply port can be reduced, and the discharge of the ink whose viscosity increase has been reduced earlier By gradually changing the flow rate, the discharge risk can be avoided, and the recovery success rate of idle discharge can be improved.

  Further, as in the second example, the idle discharge operation is performed in the order of nozzles having a low fluid resistance value in the path to the liquid supply port and nozzles having a large fluid resistance value in the path to the liquid supply port. The number of nozzles that perform idle discharge at a time is small, the pressure drop in the common liquid chamber is small, and the meniscus is less likely to be destroyed, and the recovery efficiency (recovery success rate) by the empty discharge operation can be improved.

  Here, in the configuration of the first example, even when the path of the flow path from the ink supply port to which fresh ink is supplied is the shortest, the fluid resistance value of the flow path is longer than that of the other nozzles. In the case of the head, it is not always possible to obtain the highest recovery success rate of idle ejection.

  On the other hand, it is possible to ensure a high recovery success rate by performing idle ejection from a nozzle that has the smallest fluid resistance value between the ink supply port and the nozzle path, and the ink easily flows.

  In addition, as in the third example, idle ejection is performed in units of nozzle groups in the order of a nozzle group including a plurality of nozzles having a short path to the liquid supply port and a nozzle group including a plurality of nozzles having a long path to the liquid supply port. With this configuration, the number of nozzles that perform idle discharge at a time is small, the pressure drop in the common liquid chamber is small, the meniscus is less likely to be destroyed, and the recovery efficiency (recovery success rate) due to the empty discharge operation can be improved. it can.

  And by reducing the number of nozzles to be discharged, the pressure drop in the pressurized liquid chamber and the common liquid chamber is reduced and the meniscus is less likely to break, while a plurality of adjacent nozzles having a short flow path to the liquid supply port By ejecting ink from the nozzle group formed at the same time, it is possible to efficiently attract fresh ink from the liquid supply port due to moderate negative pressure fluctuation in an area where the meniscus is not broken. The amount of fresh ink that flows in from the liquid supply port is greater when discharging the empty discharge droplets from the nozzle group than when discharging the empty discharge droplets from a single nozzle, and by controlling the number of nozzles in the nozzle group to be discharged. Thus, it is possible to obtain an optimal amount of ink flow and flow rate.

  This not only improves the recovery success rate due to the idle ejection operation, but also significantly reduces the time required for the recovery process.

  Further, as described above, the idle discharge operation is performed for each nozzle group formed by a plurality of adjacent nozzles at the beginning of the idle discharge operation, and the idle discharge operation is not performed for all the nozzles. The number of nozzles to be reduced can be reduced, and the pressure drop in the liquid chamber and common liquid chamber can be reduced to make the meniscus difficult to break, while ink is ejected from the nozzle group formed by a plurality of adjacent nozzles at the same time As a result, it is possible to efficiently attract fresh ink from the liquid supply port by an appropriate negative pressure fluctuation in a region where the meniscus is not broken. The amount of fresh ink that flows in from the liquid supply port is greater when discharging the empty discharge droplets from the nozzle group than when discharging the empty discharge droplets from a single nozzle, and by controlling the number of nozzles in the nozzle group to be discharged. Thus, it is possible to obtain an optimal amount of ink flow and flow rate.

  In addition, after each nozzle is in a state where it can perform a discharge operation, the thickened ink still remains in the corners and gaps of the flow path where ink flow is slow and in the common liquid chamber where the flow velocity is low. It has been found that this residual thickened ink can be efficiently discharged by generating an ink flow having a large flow rate in the flow path including the common liquid chamber. Therefore, after making the ink ejectable from each nozzle, in the latter stage of the idle ejection operation, all the nozzles are ejected simultaneously to generate a large flow rate, thereby discharging the thickened ink in the flow path in a short time. Can be overwhelmed.

  In the above embodiment, an example in which the ink supply port (liquid supply port) of the recording head is arranged at the center in the nozzle arrangement direction has been described. However, as shown in FIG. In the case of a recording head in which the (liquid supply port) 132 is arranged on one end side in the nozzle arrangement direction, or as shown in FIG. 9, the ink supply port (liquid supply port) 132 is on one end side in the nozzle arrangement direction. The same applies to a recording head in which the ink discharge port (liquid discharge port) 133 is disposed on the other end side in the nozzle arrangement direction.

  Further, the second example described above (an example of the magnitude of the fluid resistance value) has a plurality of nozzles 104A and 104B having different nozzle diameters, for example, as shown in FIG. 10, so that droplets of different sizes can be ejected. This is particularly effective when a liquid discharge head is used.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 11 is an explanatory diagram of the idle ejection drive waveform used in the idle ejection operation in the embodiment.
Here, as shown in FIG. 11A, the idle ejection drive waveform generation unit 703 has a plurality (N) of pulse groups PG1 to PGN (in the figure, PGN is PG6) composed of a plurality of pulses P. This is not limited to the same, and so forth.

  As shown in FIG. 12, each pulse P of the idle ejection driving waveform PE includes a meniscus pull-in period T1 for displacing the piezoelectric element (driving piezoelectric element column 121A) in the direction of expanding the volume of the liquid chamber 106, and the piezoelectric element. It is a waveform having a stop period T2 in which the displacement is stopped for a predetermined time and a meniscus push-out period T3 in which the piezoelectric element is displaced in the direction of reducing the volume of the liquid chamber 106. In this example, the pull-in period T1 is a period in which the applied voltage falls from the reference potential, the stop period T2 is a period in which the applied voltage is held at the lowered potential, and the push-out period T3 is a period in which the applied voltage rises to the reference potential. .

  Then, as shown in FIGS. 11B to 11E, each pulse P of the plurality of pulse groups PG1 to PGN is subjected to the idle discharge operation for the pulse duration Pw from the meniscus pull-in start time to the meniscus push-out end time. Each pulse P of the pulse groups PG1, PG2, PG3... PGN, in which the pulse duration of the pulse P of the pulse group PG at the beginning of the start is shorter than the pulse duration of the pulse P of the pulse group PG near the end of the idle ejection operation. The pulse duration is set to a relationship of Pw1 <Pw2 <Pw3... <PwN.

  That is, in the initial stage of the idle ejection operation, it is necessary to eject the thickened ink from the nozzle 104 in particular. Further, in the latter stage (near completion) of the idle ejection operation, most of the thickened ink has been discharged out of the nozzle 104, so that the ink having a viscosity that has not been thickened is mainly ejected.

  Here, the pulse duration Pw is an important parameter for adjusting the drop speed and drop amount of ink drops discharged from the nozzle 103, that is, the discharge energy. The pulse duration Pw at which the largest ejection energy can be obtained is a parameter linked to the Helmholtz resonance period of the liquid chamber 106.

  It has been found that the Helmholtz resonance period of the liquid chamber 106 becomes shorter as the viscosity of the ink filled in the liquid chamber 106 increases.

  Therefore, the pulse duration Pw1 of the pulse group PG1 at the start of the idle ejection operation is set to the most suitable time for ejecting ink with a large degree of thickening, and is suitable for gradually ejecting ink with low viscosity. By increasing the pulse duration time Pw, a high recovery success rate by the idle ejection operation can be obtained even in a state where various ink viscosities are mixed.

  As described above, in the initial stage of the idle ejection operation, high-viscosity ink exists near any nozzle. The degree of thickening of the ink by being left is large, and the Helmholtz resonance period of the liquid chamber filled with the ink with increased viscosity tends to be short.

  Here, in the idle ejection driving waveform in which the liquid chamber is expanded, temporarily stopped, the pressurized liquid chamber is contracted, and ink droplets are ejected from the nozzles, the pulse duration for obtaining high ejection efficiency is the Helmholtz of the liquid chamber. It is linked to the resonance period. Therefore, in a state where fresh and low-viscosity ink is filled, ink that has been left standing and increased in viscosity from the pulse duration of the idle ejection driving waveform in which ink is ejected from the nozzle with the highest ejection efficiency is filled. In FIG. 5, the pulse duration of the idle ejection drive waveform that provides the best ejection efficiency is shortened. As a result, at the beginning of the idle discharge operation, the thickened ink is efficiently driven by driving with the idle discharge driving waveform of the pulse duration that provides the highest ejection efficiency when the thickened ink is filled in the liquid chamber. It is possible to improve the recovery success rate and recovery efficiency by discharging and emptying.

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 13 is an explanatory diagram of the idle ejection drive waveform used in the idle ejection operation in the embodiment.
Here, as shown in FIGS. 13B to 13E, each pulse P of the plurality of pulse groups PG1 to PGN has a pulse P of the pulse group PG at the beginning of the idle ejection operation with respect to the interval Tw of the pulses P. The pulse interval of the pulse groups PG1, PG2, PG3,... PGN is shorter than the pulse interval of the pulses P of the pulse group PG near the end of the idle ejection operation. The relationship of <TwN is set.

  That is, similarly to the principle described in the second embodiment, the resonance period of the pulse P and the pulse P is a parameter linked to the Helmholtz resonance period of the liquid chamber 106. In order to obtain ejection energy more efficiently, it is preferable to eject the droplets from the nozzle 104 by resonating the pulse P and the pulse P.

  Therefore, in the initial stage of the idle ejection operation, the thick ink is reliably discharged out of the nozzle by driving with a plurality of pulses P with a pulse interval Tw focused on reliably ejecting the thick ink. be able to. And, as the discharge of thickened ink progresses due to idle ejection, the pulse interval Tw of the pulse P is gradually increased, and finally, it is most suitable for ejecting fresh ink that has not been thickened. By driving with pulses at a pulse interval, a high recovery success rate due to the idle ejection operation can be obtained.

  Thus, even if the ring shape of the pulse interval is the same instead of the relationship of the pulse duration in each pulse group of the second embodiment, the same effect as the second embodiment can be obtained.

  Here, for example, the ink viscosity is 8 mPa · s in the normal state, and the Helmholtz resonance period Tc of the liquid chamber 106 in a state where the ink in the normal viscosity state is filled in the liquid chamber 106 is approximately 5. .5 μsec. When the ink filled in the liquid chamber 106 is thickened by being left standing, the limit ink viscosity capable of discharging the thickened ink from the nozzle by changing the volume of the liquid chamber by driving the piezoelectric element is 90 mPa · s. It is known that the Helmholtz resonance period Tc of the liquid chamber in a state where the discharge limit ink viscosity is filled in the liquid chamber 106 is approximately 4.4 μsec.

  In other words, assuming that the ink filled in the pressurized liquid chamber has been thickened by being left and has reached the discharge limit ink viscosity, the pulse continuation of the pulse of the empty discharge driving waveform at the beginning of the empty discharge operation is continued. The time Pw and the pulse interval Tw are preferably determined by the Helmholtz resonance period that is optimal for the ejection limit ink viscosity. The viscosity of the ink filled in the pressurized liquid chamber is lowered as the ejection of the thickened ink by the idle ejection operation and the stirring of the thickened ink and the fresh ink are promoted. Therefore, it is preferable to bring the pulse duration and the pulse interval closer to the parameters corresponding to the normal viscosity in several stages assuming a decrease in viscosity in the pressurized liquid chamber.

  More specifically, the pulse duration Pw at the beginning of the idle discharge operation is shorter than the pulse duration Pw near the end of the idle discharge operation by a time that is not less than 4% and not more than 20% of the Helmholtz resonance period of the liquid chamber. The configuration. Similarly, the pulse interval Tw at the beginning of the idling operation is shorter than the pulse interval Tw near the end of the idling operation by a time that is 4% to 20% of the Helmholtz resonance period of the liquid chamber.

  In other words, the limit value of the thickened region of the ink that can be recovered by the idle ejection operation from the state where the ink in the recording head has been thickened by being left standing is about 11 times that of the normal viscosity ink state. ing. It can be seen that the Helmholtz resonance period of the pressurized liquid chamber in a normal viscosity state filled with fresh ink is shortened by about 20% with respect to the Helmholtz resonance period of the pressurized liquid chamber in the thickened state at the recovery limit. ing.

  Therefore, the pulse duration Pw and the pulse interval Pw at the beginning of the idle discharge operation are 4% or more and 20% or less of the Helmholtz resonance period of the liquid chamber, compared to the pulse duration Pw and the pulse interval Tw near the end of the idle discharge operation. By shortening this time, the idle ejection drive waveform corresponding to the lowered Helmholtz resonance period is driven to efficiently discharge the thickened ink, and gradually into the pressurized liquid chamber filled with ink of the normal viscosity state. On the other hand, by driving with the idle ejection drive waveform corresponding to the Helmholtz resonance period, it becomes possible to drive with the idle ejection drive waveform with the highest ejection efficiency of several stages of thickened ink. Increase recovery success rate.

  In addition, it is preferable to apply a driving waveform that causes the liquid chamber volume to be most reduced in the initial stage of the idle discharge operation.

  That is, in the recording head in which the volume of the pressurized liquid chamber varies depending on the pressure generating element, the pressure propagation efficiency is higher when the volume of the pressurized liquid chamber is smaller. That is, it is known that the rate of pressure increase in the pressurized liquid chamber increases with respect to the amount of displacement of the pressure generating element, and the discharge efficiency increases. Compared to the case where fresh ink is ejected from the nozzle, ejecting thickened ink from the nozzle requires more ejection energy, and the ejection energy necessary for ejection increases in proportion to the degree of thickening. . Therefore, in the initial stage of the empty discharge operation, an empty discharge driving waveform is applied to the pressure generating means so that the volume of the liquid chamber is minimized, and the volume of the pressurized liquid chamber is further reduced to increase the discharge efficiency. By applying the idle ejection driving waveform, it is possible to widen the limit viscosity region in which droplets can be ejected from the nozzle.

Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 14 is an explanatory diagram for explaining the idle ejection driving waveform in the embodiment.
This idle discharge drive waveform has a pulse group AN (A1... AN) composed of a plurality of pulses P driven at an interval that is an integral multiple of the Helmholtz resonance period of the pressurized liquid chamber. It has a continuous discharge period BN (B1... BN) that is continuously driven at TfN (Tf1... TfN).

  During the continuous driving period BN of the pulse group AN, the maximum displacement pulse Pmax for destroying the film on which the solid component of the ink formed on the nozzle edge and the meniscus surface is deposited, and for discharging the film out of the nozzle by ejection. Have

  Here, the pulse group interval TfN is preferably equal to or longer than the refill cycle (liquid supply cycle) in order to avoid supply shortage and ensure ejection in a state where the influence of the preceding empty ejection droplets is reduced.

  In order to shorten the idle discharge time, the pulse group interval TfN is gradually shortened from the beginning of the idle discharge operation to the latter stage of the idle discharge operation (Tf1> Tf2>...> TfN).

  Further, it is preferable to gradually increase the number of times of driving AN in the pulse group from the beginning of the idle ejection operation to the latter stage of the idle ejection operation in accordance with the decrease in the fluid resistance value accompanying the discharge of the thickened ink.

  And at the meniscus drawing start point of the maximum displacement pulse Pmax, it is preferable to drive with the maximum applied voltage in the direction of reducing the volume of the pressurized liquid chamber. Further, as shown in FIG. 15, the meniscus pull-in time Tx of the maximum displacement pulse Pmax is a time longer than the Helmholtz resonance period Tc of the pressurized liquid chamber so that the meniscus is not broken and bubbles are trapped in the liquid chamber. It is preferable that (Tx ≧ Tc).

  Due to the meniscus pull-in driving of the maximum displacement pulse Pmax, a large amount of ink flows into the pressurized liquid chamber as the volume of the pressurized liquid chamber increases. As the ink flows into the pressure liquid chamber, the pressure in the pressure liquid chamber gradually increases. At this time, it is preferable to start the meniscus extrusion drive in a state where the pressure in the pressurized liquid chamber has increased to the maximum. Therefore, as shown in FIG. 15, the time (Tx + Tz) from the start of the meniscus drawing of the maximum displacement pulse Pmax to the end of the stop period is a refill cycle so that a sufficient amount of ink inflow time can be secured in the pressurized liquid chamber. It is preferable to secure a period of 1/2 or more.

  Further, the meniscus extrusion time Tf of the maximum displacement pulse Pmax is increased in order to destroy the deposited film formed on the edge portion of the nozzle 104 and the meniscus, and to destroy the deposited film in the vicinity of the nozzle together with the ink. A period shorter than the Helmholtz resonance period Tc of the pressurized fluid chamber (Ty <Tc) is preferable.

  In addition, when continuously driven with the maximum displacement pulse Pmaz, the volume fluctuation width and pressure amplitude of the pressurized liquid chamber are too large, the meniscus formed in the nozzle 104 is destroyed, ink overflow, and bubbles inside the nozzle 104 Since the entrainment is likely to occur, the maximum displacement pulse Pmax is usually preferably given in a single manner with a time interval between the idle ejection pulses, and here, it is applied between the continuous ejection periods BN. I am doing so.

  In other words, due to the moisture state due to leaving, the edge portion of the nozzle and the meniscus surface formed on the nozzle are in a state where a solid component of ink is deposited to form a film, and this nozzle is proportional to the boundary and the leaving time. The thickness of the film formed on the edge portion and the meniscus surface increases. And as it increases, it becomes difficult to eject droplets from the nozzles. Even after the film has been formed, in order to eject ink from the nozzles, it is necessary to first destroy the film. As the film thickness increases, the discharge energy necessary to break the film, that is, the pressure inside the nozzle and the inside of the pressurized liquid chamber needs to be increased instantaneously. However, if the pressure is too high, the meniscus overflows from the nozzle and the pressure increases. If it is too low, the meniscus is destroyed and bubbles are entrained in the liquid chamber.

  Therefore, although it is desired to vibrate the pressure generating element greatly in the idle ejection driving waveform for breaking the film, the number of times of driving by the pulse needs to be about once per unit time so as not to cause ink overflow or meniscus destruction. . However, it is difficult to reliably destroy the film of all the nozzles by a single drive.

  Therefore, it is possible to break the nozzle film and discharge the thickened ink without causing ink overflow or meniscus breakage by driving a plurality of times at intervals.

  Further, in the maximum displacement pulse, the meniscus pulling displacement time for displacing the liquid chamber volume from the most contracted state to the most expanded state after completion of the continuous discharge period is longer than the Helmholtz resonance period of the liquid chamber. It is preferable to do.

  As a result, the maximum displacement pulse can be driven under a condition in which the nozzle meniscus in a state where the film has been broken and ink can be ejected is broken and the phenomenon of entraining bubbles does not occur.

  Also, after the end of the continuous discharge period in the maximum displacement pulse, the liquid chamber volume is displaced from the most contracted state to the most expanded state, stopped for a certain period of time, and then the meniscus which is displaced again to the state in which the liquid chamber volume is further reduced. The extrusion displacement time is preferably shorter than the Helmholtz resonance period of the liquid chamber.

  As a result, even when a nozzle is formed with a film or a film that is about to be destroyed remains in the vicinity of the meniscus, it can be driven with a drive waveform having discharge energy that can be discharged out of the nozzle. It is possible to improve the destruction efficiency of the steel and to improve the discharge efficiency of the destroyed precipitates, and to increase the recovery success rate by idle discharge.

  In addition, after the end of the continuous discharge period in the maximum displacement pulse, the liquid chamber volume is displaced from the most reduced state to the most expanded state, and the displacement for a certain period of time is changed again to the state in which the liquid chamber volume is further reduced. The displacement stop time for stopping is preferably 1/2 or more of the liquid supply cycle of the flow path communicating with the nozzle.

  That is, when driven by the maximum displacement pulse, a large amount of ink flows from the ink supply port or the common liquid chamber toward the pressurized liquid chamber during the meniscus pull-in period in which the pressurized liquid chamber is expanded from the most contracted state. To do. By setting the time from the start of the meniscus pull-in to the start of the meniscus push to be 1/2 or more of the refill cycle, the meniscus push-out period is started in the region where the amount of ink flowing into the pressurized liquid chamber is the largest. Is possible.

  As the amount of ink flowing into the pressurized liquid chamber increases, the pressure in the pressurized liquid chamber increases, and in this state, the pressure liquid chamber is rapidly reduced to obtain a large pressure increase in the pressurized liquid chamber. In the meniscus extrusion period, the success rate of breaking the film formed on the nozzle can be greatly improved.

  Moreover, it is preferable that the application of the maximum displacement pulse is started after a time equal to or longer than the liquid supply cycle (refill cycle) of the nozzle has elapsed after the end of the continuous discharge period.

  That is, when the maximum displacement pulse has a large meniscus displacement during the meniscus pull-in period and the position where the meniscus is formed at the start of the meniscus pull-in period is in the meniscus formation limit region on the negative pressure side in the nozzle, the meniscus is further reduced. By applying the pulling load, the meniscus is destroyed and there is a high possibility that air bubbles are involved in the liquid chamber. In the nozzle where the film formed on the nozzle is not broken, meniscus breakage is unlikely to occur, but in the state where the film is broken and ink can be ejected, the meniscus can be freely displaced greatly It has become. In addition, the meniscus amplitude width immediately after the ink ejection operation from the nozzle is large, and it is not preferable that the maximum displacement pulse is driven in a state where the meniscus is largely drawn at this amplitude.

  Therefore, by ensuring a stop period equal to or longer than the refill cycle after the continuous discharge period, it is possible to avoid the occurrence of a decrease in bubble entrainment in a nozzle in a state where ink can be discharged.

  Moreover, it is preferable that after the application of the maximum displacement pulse is finished, the next continuous discharge period is started after a time equal to or longer than the liquid supply cycle of the nozzle has elapsed.

  That is, the high pressure chamber continues in the pressurized liquid chamber in the period within the refill cycle immediately after the maximum displacement pulse drive. Immediately after the maximum displacement pulse is driven, the meniscus amplitude is small in the nozzle in which the film is not broken. However, in a nozzle immediately after the film is broken or in a state where ink can be ejected, the meniscus swells greatly, and if so, it overflows slightly. A nozzle with a large swelled meniscus or even a slight ink overflow has greatly reduced ejection efficiency, making it difficult to form a meniscus state suitable for ink ejection. If the idle ejection drive waveform having a large ejection energy is driven, ink is not ejected and the ink overflow state is further promoted, and the recovery success rate of idle ejection is significantly reduced.

  Therefore, it is known that the meniscus amplitude raised by the maximum displacement pulse is sufficiently attenuated by leaving the refill cycle period immediately after the maximum displacement pulse drive, and after stopping for a period longer than the refill cycle immediately after the maximum displacement pulse drive, By driving the continuous ejection pulse, the ink overflow can be avoided.

Next, a fifth embodiment of the present invention will be described with reference to FIG. FIG. 16 is an explanatory diagram for explaining the idle ejection driving waveform in the embodiment.
In this idle ejection drive waveform, the number of pulses constituting the pulse group AN in the initial stage of the idle ejection operation is small, and the number of pulses constituting the pulse group AN in the late stage of the idle ejection operation is large.

  That is, since the ratio of thickened ink is high at the beginning of the idle ejection operation, if the ink flow rate per unit time increases, the phenomenon that the meniscus formed on the nozzle is destroyed due to insufficient ink supply and bubbles are involved. It is easy to do. Therefore, it is preferable to implement low frequency driving. The idle discharge time can be shortened by gradually increasing the drive cycle of the idle discharge drive waveform from the initial stage of the idle discharge operation to the late stage of the idle discharge operation. It is also preferable to gradually increase the number of times of idle discharge driving in unit time.

  In this way, it is preferable that the amount of droplets discharged per unit time from each nozzle at the beginning of the idle discharge operation is smaller than the amount of droplets discharged per unit time from each nozzle near the end of the idle discharge operation. .

  That is, at the beginning of the idle ejection operation, the ink that has increased viscosity exists in the nozzles and in the flow paths such as the pressurized liquid chamber and the common liquid chamber. In such a state, when the ink flows, the fluid resistance value is high, the negative pressure in the liquid chamber is high, the meniscus is destroyed due to insufficient supply, and the risk of entraining bubbles inside the nozzle is high.

  Therefore, by reducing the drive frequency of the idle ejection pulse group or reducing the number of times of driving, the ink flow rate per unit time at the beginning of idle ejection can be reduced, and the occurrence of insufficient supply can be suppressed. . As the viscosity of the ink in the liquid chamber decreases with the idle ejection time, the idle frequency can be completed in a shorter time by gradually increasing the drive frequency and the number of times of driving per unit time. It becomes possible.

Next, a sixth embodiment of the present invention will be described with reference to FIG. FIG. 17 is an explanatory diagram for explaining the idle ejection driving waveform in the embodiment.
In the idle ejection driving waveform, the peak value Vm of the pulse at the beginning of the idle ejection operation is high, and the peak value Vm of the pulse at the latter stage of the idle ejection operation is low (Vm1>Vm2> Vm3).

  That is, at the beginning of the idle ejection operation, the degree of viscosity increase and the ratio of the thickened ink in the liquid chamber are in a high state. Therefore, at the initial start of the idle ejection operation, the ink is driven with an idle ejection drive waveform having a large ejection energy that is dropped to eject the thickened ink.

  As shown in FIG. 18, the above-described idle ejection operation is preferably performed by ejecting idle ejection droplets toward the inside of the cap 82 in a state where the nozzle surface 34a of the recording head 34 is capped by the cap 82. In this case, the cap 82 is in communication with the atmosphere. An absorbing member 90 is disposed in the cap 82. Further, in this case, when a plurality of caps 82 are provided, other than one cap 82 is connected via a valve 91 as shown in FIG.

  When the ink is ejected while being capped, since the nozzle surface 34a and the ink droplet landing position in the cap 82 are close to each other, a larger amount of ejected ink is landed on the ink receiving portion in the cap 82 and the ink adhering to the nozzle surface is removed. Decrease drastically. Further, even if a large amount of satellites are generated in the idle discharge, the mist that is diffused in the apparatus hardly occurs because of the idle discharge that is performed in the capping state. Further, the ink ejected from the nozzle has a specific gravity much higher than that of air, so that it moves quickly to the lower part of the cap 82. When the capping empty discharge is performed in the atmosphere communication state, the ink discharged from the nozzle 104 flows to the lower portion of the cap 82 and is discharged, and even if more ink is discharged from the nozzle, the ink is pushed out from the lower portion of the cap 82 at the same time. Therefore, even if no special control (suction operation or the like) is performed, the ink discharged to the cap does not come into contact with the nozzle surface.

  That is, as described above, when the apparatus is left unattended, the solid component is deposited on the edge portion of the nozzle or the meniscus surface formed on the nozzle due to ink thickening inside the liquid chamber or evaporation of moisture from the nozzle. Occurs. Therefore, by performing the idle ejection operation as described above, the film formed on the edge portion of the nozzle and the meniscus surface is destroyed, the thickened ink inside the nozzle is surely discharged, and the ink can be ejected normally from the nozzle. It can be restored to the state.

  Here, in the idle ejection operation, if the piezoelectric element is driven with the idle ejection drive waveform with extremely large ejection energy in order to eject the thickened ink, the idle ejection amount (cannot be ejected) in proportion to the standing time. The amount of ink that must be increased).

  However, among a plurality of nozzles formed on the recording head, a nozzle that recovers to a state where it can be ejected sooner depending on the leaving time, the leaving environment, the location of the nozzle, and the state of the nozzle and cap before leaving, and the nozzle that does not recover easily Will occur. In order to secure the recovery success rate by the idle discharge operation with a margin, it is necessary to implement the idle discharge control that reliably recovers even nozzles that do not recover easily. It is necessary to drive and increase the amount of ejected droplets.

  At this time, if the nozzle and the liquid chamber that can be normally ejected are driven by the idle ejection driving waveform having a large ejection energy, the strength of the ejection air flow generated by the idle ejection is increased by ejecting the ink droplet having a high flying speed. It increases and it becomes easy to scatter an empty discharge droplet to places other than an empty discharge receptacle. However, since a droplet having a high flying speed generates a large number of satellites, a mist phenomenon occurs in which a large amount of satellites are scattered in the apparatus along the discharge airflow.

  Therefore, by performing idle ejection while capping the nozzle surface, by performing idle ejection on the cap in a state close to a flat space, it is possible to ensure a state in which almost no airflow is generated due to ejection, and further, nozzles and ink Since the landing positions are close to each other, most of the ejected ink including the satellite ejected by the idle ejection can be landed and captured in the cap. That is, it is possible to reduce or eliminate mist scattered in the apparatus during idle discharge.

  Also, by performing idle ejection while the inside of the cap communicates with the atmosphere, regardless of the amount of ink ejected due to capping idle ejection, ink with a large specific gravity is ejected to the outside of the cap. Without performing this special control, it is possible to avoid the phenomenon that the discharged ink and the nozzle surface come into contact with each other.

  The image forming apparatus according to the present invention is not limited to a printer having a single function configuration, and may be an image forming apparatus having a composite function such as printer / facsimile / copying.

10 Ink cartridge 33 Carriage 34, 34a, 34b Recording head (liquid ejection head)
81 Maintenance / Recovery Mechanism 82a Cap 508 Print Control Unit 703 Empty Discharge Drive Waveform Generation Unit

Claims (19)

A plurality of nozzles for discharging droplets; a liquid chamber in which each nozzle communicates; a common liquid chamber for supplying a liquid to each liquid chamber; a liquid supply port for supplying the liquid to the common liquid chamber; and the liquid chamber A pressure generating means for generating pressure to pressurize the liquid, and a recording head,
Empty discharge control means for performing an empty discharge operation for discharging empty discharge droplets that do not contribute to image formation from each nozzle of the recording head, and
The image forming apparatus according to claim 1, wherein the idle ejection control unit performs an idle ejection operation in order of a nozzle having a short path to the liquid supply port and a nozzle having a long path to the liquid supply port. A plurality of nozzles for discharging droplets; a liquid chamber in which each nozzle communicates; a common liquid chamber for supplying a liquid to each liquid chamber; a liquid supply port for supplying the liquid to the common liquid chamber; and the liquid chamber A pressure generating means for generating pressure to pressurize the liquid, and a recording head,
Empty discharge control means for performing an empty discharge operation for discharging empty discharge droplets that do not contribute to image formation from each nozzle of the recording head, and
The idle ejection control means causes the idle ejection operation to be performed in the order of a nozzle having a small fluid resistance value in a path to the liquid supply port and a nozzle having a large fluid resistance value in the path to the liquid supply port. Forming equipment. A plurality of nozzles for discharging droplets; a liquid chamber in which each nozzle communicates; a common liquid chamber for supplying a liquid to each liquid chamber; a liquid supply port for supplying the liquid to the common liquid chamber; and the liquid chamber A pressure generating means for generating pressure to pressurize the liquid, and a recording head,
Empty discharge control means for performing an empty discharge operation for discharging empty discharge droplets that do not contribute to image formation from each nozzle of the recording head, and
The image forming apparatus according to claim 1, wherein the idle ejection control unit performs an idle ejection operation in order of a nozzle group having a short path to the liquid supply port and a nozzle group having a long path to the liquid supply port.   The idle discharge control means performs idle discharge operation for each nozzle group composed of a plurality of adjacent nozzles at the beginning of the idle discharge operation, and does not perform idle discharge from all the nozzles at the beginning of the idle discharge operation. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   5. The image forming apparatus according to claim 1, wherein the idle ejection control unit causes idle ejection from all the nozzles simultaneously in a later stage of the idle ejection operation. The pressure generating means is a piezoelectric element;
The idle ejection drive waveform for driving the piezoelectric element by the idle ejection operation includes a meniscus pull-in period for displacing the piezoelectric element in the direction of expanding the volume of the liquid chamber, and a stop for stopping the displacement of the piezoelectric element for a certain period of time. A plurality of pulse groups including one or a plurality of pulses having a period and a meniscus extrusion period for displacing the piezoelectric element in a direction to reduce the volume of the liquid chamber,
The pulse continuation time from the start of the meniscus pull-in of the pulse of the pulse group to the end of meniscus push-out at the initial start of the idle discharge operation is the start of the meniscus pull-in of the pulse of the pulse group near the end of the idle discharge operation. 6. The image forming apparatus according to claim 1, wherein the image forming apparatus is shorter than a pulse duration from the end of meniscus extrusion to the end of meniscus extrusion.   The pulse continuation time from the start of the meniscus pull-in of the pulse of the pulse group to the end of meniscus push-out at the initial start of the idle discharge operation is close to the end of the idle discharge operation. 7. The image forming apparatus according to claim 6, wherein the image forming apparatus is shorter than the pulse duration from the time point to the end point of meniscus extrusion by a time of 4% to 20% of the Helmholtz resonance period of the liquid chamber. The pressure generating means is a piezoelectric element;
In the idle ejection driving waveform for driving the piezoelectric element by the idle ejection operation, the piezoelectric element is displaced in the direction of expanding the volume of the liquid chamber, the meniscus pull-in period, and the stop for stopping the displacement of the piezoelectric element for a certain period of time. A plurality of pulse groups including a plurality of pulses having a period and a meniscus extrusion period for displacing the piezoelectric element in a direction to reduce the volume of the liquid chamber,
6. The pulse interval of the pulse group at the beginning of the idle discharge operation is shorter than the pulse interval of the pulse group near the end of the idle discharge operation. The image forming apparatus described in 1.   The pulse interval of the pulse group at the beginning of the idle discharge operation is 4% or more and 20% of the Helmholtz resonance period of the liquid chamber, rather than the pulse interval of the pulse group near the end of the idle discharge operation. 9. The image forming apparatus according to claim 8, wherein the pulse interval is shorter by the following time.   The image forming apparatus according to claim 1, wherein the volume of the liquid chamber is minimized with respect to the pressure generating unit at the beginning of the idle discharge operation. The pressure generating means is a piezoelectric element;
In the idle ejection driving waveform for driving the piezoelectric element by the idle ejection operation, the piezoelectric element is driven by a pulse group consisting of a plurality of pulses repeated at a cycle interval longer than the liquid supply cycle of the flow path communicating with the nozzle. Including a continuous discharge period
In the interval between the continuous discharge periods, the piezoelectric element is displaced from the state in which the volume of the liquid chamber is most reduced to the state in which it is most expanded, is stopped for a certain period in the expanded state, and is further displaced in a state of being further reduced. 6. The image forming apparatus according to claim 1, further comprising a pulse.   In the maximum displacement pulse, the meniscus pulling displacement time for displacing the liquid chamber volume from the most contracted state to the most expanded state after the continuous discharge period is longer than the Helmholtz resonance period of the liquid chamber. The image forming apparatus according to claim 11.   In the maximum displacement pulse, after the continuous discharge period ends, the liquid chamber volume is displaced from the most contracted state to the most expanded state, and after a certain period of stoppage, the liquid chamber volume is further reduced to the most contracted state. 13. The image forming apparatus according to claim 11, wherein the meniscus push-out displacement time is shorter than a Helmholtz resonance period of the liquid chamber.   In the maximum displacement pulse, after the continuous discharge period is completed, the liquid chamber volume is displaced from the most contracted state to the most expanded state, and is again fixed for a certain period of time when the liquid chamber volume is displaced to the most contracted state again. The image forming apparatus according to claim 11, wherein a displacement stop time for stopping the displacement is ½ or more of a liquid supply cycle of a flow path communicating with the nozzle.   The image forming apparatus according to claim 11, wherein after the continuous discharge period ends, application of the maximum displacement pulse is started after a time equal to or longer than a liquid supply period of the nozzle has elapsed. .   16. The next continuous discharge period is started after a time equal to or longer than the liquid supply cycle of the nozzle has elapsed after the application of the maximum displacement pulse is completed. Image forming apparatus.   The amount of droplets discharged from each nozzle at the beginning of the idle discharge operation in a unit time is smaller than the amount of droplets discharged from each nozzle near the end of the idle discharge operation in a unit time. The image forming apparatus according to claim 1.   18. The image forming apparatus according to claim 1, wherein the discharge energy of the pressure generating unit is greater at the start of the idle ejection operation than near the end of the idle ejection operation.   19. The idle discharge operation according to claim 1, wherein an empty discharge droplet is discharged toward the inside of the cap member in a state where the nozzle surface of the recording head is capped with the cap member. Image forming apparatus.

Images