JP2010094871A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device which can discharge thickened ink effectively while minimizing the generation of mist. <P>SOLUTION: Idle delivering operation is carried out by applying four continuous drive pulses P1 through P4 as idle delivering drive pulses, and the droplet speed (delivering speed) of a plurality of idle delivering droplets to be delivered by the drive pulses P1 through P4 is set to become lower stepwise. The droplet speed of the idle delivering droplet which is delivered lastly by the drive pulse P4 is the droplet speed generating no satellite, and is set lower than the droplet speed of the idle delivering droplet which is delivered firstly. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  In general, a printer, a fax machine, a copier, a plotter, or an image forming apparatus that combines a plurality of these functions includes, for example, a recording head composed of a liquid ejection head that ejects ink droplets, It is also referred to as “paper”, but the material is not limited, and a recording medium, recording medium, transfer material, recording paper, etc. are also used synonymously.) Some perform formation (recording, printing, printing, and printing are also used synonymously).

  The “image forming apparatus” means an apparatus for forming an image by discharging a liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, etc. In addition to providing an image having a meaning such as a figure to a medium, it also includes a device for applying an image having no meaning such as a pattern to the medium (simply ejecting droplets). The “ink” is not limited to so-called ink, and is not particularly limited as long as it becomes a liquid when ejected. For example, a liquid including a DNA sample, a resist, a pattern material, and the like. Used as a general term.

  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, since the liquid discharge head constituting the recording head used in the image forming apparatus performs recording by discharging droplets from the discharge ports, the viscosity of the ink in the discharge ports is maintained when the state in which no droplets are discharged continues. When the droplet discharge operation is performed as it is, the discharge state is disturbed, the discharge is impossible, and the printing quality is deteriorated. Therefore, the droplet (not contributing to recording (image formation) from the nozzle ( By discharging a liquid droplet as waste liquid, which is referred to as “empty discharge droplet”), an empty discharge operation for discharging the thickened ink is performed.

  In this case, since the purpose of the ejected droplets ejected in the idle ejection operation is to discharge the thickened ink as described above, the drive pulse applied to the recording head during the idle ejection operation is recorded during normal image formation. The driving pulse is stronger than the driving pulse applied to the head (pulse with a fast droplet velocity). As a result, there is a problem that droplets ejected by a strong drive pulse have a high ejection speed and mist due to minute droplets such as satellites increases.

  In the idle ejection operation, the nozzle surface of the recording head is idly ejected into the cap that seals the nozzle surface of the recording head, or is ejected idly toward the idle ejection receiver that receives the dedicated idle ejection droplets. The distance to the landing site of the empty ejected droplets is relatively longer than the distance between the recording head and the paper during normal image formation.Therefore, the drop in satellite droplet speed is greatly reduced due to air resistance. Mist is more likely to occur.

  Therefore, conventionally, as described in Patent Document 1, with respect to the idle ejection operation, there is provided means for changing the distance between the droplet ejection unit and the droplet landing unit during the maintenance operation, and driving is performed corresponding to the distance. It is known to change the signal to make the droplet velocity constant upon landing.

  Further, as described in Patent Document 2, it is known to provide a drive signal that causes only a main droplet to be a droplet during idle ejection.

  Further, as described in Patent Document 3, when a droplet that does not contribute to image formation is ejected from the head, the maximum droplet velocity is equal to or higher than the maximum droplet velocity when ejecting a droplet that contributes to image formation. It is known to eject droplets having a droplet velocity twice or less of the above.

JP2007-9829A Japanese Patent No. 3284502 JP 2007-283649 A

  However, as described in Patent Document 1 described above, if the droplet velocity at the time of landing of the droplet landing portion is to be constant, if the distance from the landing portion is long, inevitably at the time of discharge. Since the droplet velocity increases and satellites increase, there is a problem that mist generation also increases.

  Further, as described in Patent Document 2, if the driving pulse is such that no satellite is generated, the ejection speed cannot be increased, and the force for discharging the thickened ink in the nozzle is weakened. It becomes difficult to achieve the original purpose of empty discharge. In addition, Patent Document 2 describes that the satellite can be merged with the subsequent main droplet by increasing the discharge frequency, so that the waveform setting range is widened. As the satellite rises, the satellite becomes a mist before merging due to the influence of the air flow generated by ejecting droplets, so the thickened ink that is the original purpose of empty ejection is discharged without generating mist It becomes difficult to let you.

  The present invention has been made in view of the above-described problems, and an object thereof is to effectively discharge thickened ink while suppressing generation of mist.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A recording head having nozzles for discharging droplets;
Means for performing an empty discharge operation for continuously discharging a plurality of empty discharge droplets that do not contribute to image formation from the recording head,
The droplet speed of the empty discharge droplet that is discharged last among the plurality of empty discharge droplets is a droplet speed at which no satellite is generated, and a droplet speed that is lower than the droplet speed of the empty discharge droplet that is discharged first It was.

  Here, the droplet speed of the plurality of empty ejection droplets can be reduced stepwise.

  Further, the plurality of empty ejection droplets may include a plurality of merged droplets during flight, and the plurality of merged droplets may have a drop speed that gradually decreases.

  Further, the plurality of empty ejection droplets include a droplet ejected at a timing that resonates with pressure vibration of a liquid chamber that communicates with the nozzle of the recording head, and a droplet ejected at a timing that does not resonate with the pressure vibration. In other words, the last discharged empty discharged droplet may be a droplet discharged at a timing that does not resonate with the pressure vibration.

An image forming apparatus according to the present invention includes:
A recording head having nozzles for discharging droplets;
Means for performing an empty discharge operation for continuously discharging a plurality of empty discharge droplets that do not contribute to image formation from the recording head,
The droplet speed of the empty discharge droplet that is discharged last among the plurality of empty discharge droplets is configured to be lower than the droplet speed of the empty discharge droplet that is discharged first.

  According to the image forming apparatus of the present invention, when performing a blank ejection operation, a plurality of blank ejection droplets are ejected, and the droplet speed of the blank ejection droplet to be ejected last among the plurality of blank ejection droplets is generated by satellites. The drop speed is not higher and the drop speed is slower than that of the first empty discharge droplet, so that it is relatively fast from the first empty discharge droplet to the last empty discharge droplet. Mist caused by the generation of satellites can be reduced by discharging the ink thickened by the empty ejected droplets at the droplet speed to form the last ejected ejected droplet having a relatively slow speed.

  According to the image forming apparatus of the present invention, when performing the idle ejection operation, the plurality of idle ejection droplets are ejected, and the droplet speed of the idle ejection droplet to be ejected last among the plurality of idle ejection droplets is the first ejection rate. The ink is thicker than the first empty discharge droplet until the last empty discharge droplet. , And the generation of satellites can be suppressed and mist can be reduced by slowing the drop speed of the last empty discharge drop.

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. 2 via a timing belt by a main scanning motor (not shown).

  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. 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 positive output and a negative output are alternately repeated with respect to the charging roller 56, that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 51 alternates, that is, in a sub-scanning direction that is a circumferential direction. , Plus and minus are alternately charged in a band shape with a predetermined width. When the paper 42 is fed onto the conveyance belt 51 charged alternately with plus and minus, the paper 42 is attracted to the conveyance belt 51, and the paper 42 is conveyed in the sub-scanning direction by the circular movement of the conveyance 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).

  This liquid discharge head includes, for example, a flow path plate 101 formed by anisotropic etching of a single crystal silicon substrate, a vibration plate 102 formed by, for example, nickel electroforming bonded to the lower surface of the flow path plate 101, a flow path A nozzle plate 103 joined to the upper surface of the plate 101 is joined and laminated, and a nozzle communication path 105 that is a flow path through which a nozzle 104 that discharges droplets (ink droplets) communicates therewith and a liquid chamber that is a pressure generation chamber. 106, an ink supply port 109 communicating with a common liquid chamber 108 for supplying ink to the liquid chamber 106 through a fluid resistance portion (supply path) 107 is formed.

  In addition, two rows (only one row is shown in FIG. 3) of stacked piezoelectric elements as electromechanical conversion elements that are pressure generating means (actuator means) for pressurizing the ink in the liquid chamber 106 by deforming the diaphragm 102. An element 121 and a base substrate 122 to which the piezoelectric element 121 is bonded and fixed are provided. Note that a column portion 123 is provided between the piezoelectric elements 121. This support portion 123 is a portion formed simultaneously with the piezoelectric element 121 by dividing and processing the piezoelectric element member. However, since the drive voltage is not applied, the support portion 123 becomes a simple support. Further, an FPC cable 126 equipped with a drive circuit (drive IC) (not shown) is connected to the piezoelectric element 121.

  The peripheral edge of the diaphragm 102 is joined to a 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 including the piezoelectric element 121 and the base substrate 122. A recess and an ink supply hole 132 for supplying ink from the outside to the common liquid chamber 108 are formed. The frame member 130 is formed by injection molding with a thermosetting resin such as an epoxy resin or polyphenylene sulfite, for example.

  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 121 and the support post 123 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 element 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 element 121 alternately. 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 element 121. However, the pressure in the d31 direction is used as the piezoelectric direction of the piezoelectric element 121. The ink in the liquid chamber 106 may be pressurized. Alternatively, a structure in which one row of piezoelectric elements 121 is provided on one substrate 122 may be employed.

  In the liquid discharge head having such a configuration, for example, by lowering the voltage applied to the piezoelectric element 121 from the reference potential, the piezoelectric element 121 contracts, and the diaphragm 102 descends to expand the volume of the liquid chamber 106. Then, the ink flows into the liquid chamber 106, and then the voltage applied to the piezoelectric element 121 is increased to extend the piezoelectric element 121 in the stacking direction, and the diaphragm 102 is deformed in the direction of the nozzle 104, so that the volume / volume of the liquid chamber 106 is increased. By contracting the volume, the ink in the liquid chamber 106 is pressurized, and ink droplets are ejected (ejected) from the nozzle 104.

  Then, by returning the voltage applied to the piezoelectric element 121 to the reference potential, the diaphragm 102 is restored to the initial position, and the liquid chamber 106 expands to generate a negative pressure. 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. This figure is an overall block diagram of the control unit.
The control unit 500 includes a CPU 511 that also functions as a unit for controlling the idle discharge 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, image data, and the like. 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 that processes 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, An AC bias is applied to the charging roller 56, a main scanning motor 554 that moves and scans the carriage 33, a sub-scanning motor 555 that rotates the conveyance belt 51, a motor drive unit 510 that drives the maintenance / recovery motor 556 of the maintenance / recovery mechanism 81. An AC bias supply unit 511 and the like are provided.

  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 7 is driven by applying it to a driving element (for example, a piezoelectric element) that generates 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.
As described above, 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 printing cycle at the time of image formation. 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) within the idle ejection cycle, and 2-bit image data (gradation) corresponding to the print image And a data transfer unit 702 that outputs a clock signal, a latch signal (LAT), and droplet control signals M0 to M3.

  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.

Next, the idle ejection drive pulse (common drive waveform) in the first embodiment of the present invention will be described with reference to FIG.
From the drive waveform generation unit 701, within one discharge period (one drive period), as shown in FIG. 7, the waveform element falls from the reference potential Ve and the hold state from the state after the fall (the potential does not change). A blank ejection drive signal (drive waveform) composed of a plurality of (in this case, four) drive pulses P1 to P4 composed of waveform elements and the like that rise through a portion) is generated and output.

  Here, the waveform element in which the potential V of the drive pulse falls from the reference potential Ve is a drawing waveform element in which the piezoelectric element 121 contracts and the volume of the pressurized liquid chamber 106 expands. Further, the waveform element that rises from the state after the fall is a pressurizing waveform element that causes the piezoelectric element 121 to expand and the volume of the pressurized liquid chamber 106 to contract.

  In addition, the drive pulses P1 to P4 are set to timings at which droplet ejection is performed at a timing that resonates with pressure vibration in the liquid chamber 106 generated by droplet ejection by the drive pulses before the drive pulse. Thereby, for example, the ejection speed of the droplets ejected by the drive pulse P2 applied after ejection of the empty ejection droplets by the drive pulse P1 is faster than the ejection speed of the droplets when ejected by the drive pulse P2 alone. .

  Further, the waveform element of the drive pulse P1 is set so that the ejection speed by the drive pulse P1 for ejecting the empty ejection droplets first becomes, for example, 10 m / sec or more, and then the ejection speed by the drive pulse P2 for ejecting the empty ejection droplets Is set to a waveform element that is slower than the ejection speed by the drive pulse P1. Similarly, the ejection speed by the driving pulse P3 for ejecting the empty ejection droplet is set to a waveform element that is slower than the ejection speed by the driving pulse P2, and finally the ejection speed by the driving pulse P4 for ejecting the empty ejection droplet is driven. The waveform element is set to a waveform speed that is slower than the ejection speed by the pulse P3 and has a droplet speed at which no satellite is generated. That is, the droplet speeds of the plurality of empty ejection droplets ejected by the drive pulses P1 to P4 are configured to be gradually decreased.

  For example, the drive pulse P4 for finally discharging the empty discharge droplet is set so that the empty discharge droplet is discharged at a droplet speed of 8 m / sec or less. As conditions for generating satellites, it was confirmed experimentally that when the ink used in the present embodiment is used, satellites are generated when the discharge speed exceeds 8 m / s, and satellites are not generated below that. Therefore, it is set so as to have the above-described drop velocity. The generation of satellites is related to the surface tension and viscosity of the ink. The ink meniscus extends from the nozzle (a shape that dripping water droplets), and when a certain critical point is reached, droplets are ejected. Depending on the timing of the extension, it is determined whether everything is absorbed by the ejected droplets or separated as satellites, and is largely governed by the characteristics of the ink. Therefore, the waveform element of the drive pulse may be set so that the droplet velocity does not generate satellites according to the ink characteristics of the apparatus.

  Here, as the waveform element of the drive pulse, the droplet discharge speed by each of the drive pulses P1 to P4 is made different by changing the peak value of the drive pulse (it is gradually reduced). The droplet discharge speed can also be varied by varying the rising time constant as the waveform element.

  With this configuration, in the first ejection of the drive pulse P1 alone, the ejection speed of the ejection droplet is high, and the thickened ink can be effectively discharged into the nozzle. Although a large amount of droplets are generated, the droplets are ejected by the four drive pulses P1 to P4 continuously, and the ejection speed is gradually reduced, so that the four ejected droplets are merged during the flight. It is possible to fly without dropping, and to discharge without generating satellite-like microdroplets between the droplets and after the last droplet.

  In this way, when performing the idle ejection operation, the droplet speed of the idle droplet that is discharged at the end of the plurality of empty droplets is a droplet velocity at which no satellite is generated, and Since the drop velocity is slower than the first empty discharge droplet, it is a relatively fast empty droplet before the first empty discharge droplet reaches the last empty discharge droplet. By discharging the thickened ink and making it the last empty ejected droplet having a relatively low speed, it is possible to reduce mist due to the generation of satellites.

  In other words, the first empty discharge droplet is configured such that the droplet speed of the empty discharge droplet to be discharged last among the plurality of empty discharge droplets is lower than the drop velocity of the empty discharge droplet to be discharged first. The ink that has been thickened with a relatively fast drop velocity before discharging until the last empty discharge droplet is discharged, and the generation of satellites is suppressed by slowing the drop velocity of the last empty discharge droplet, Mist can be reduced.

Next, the idle ejection drive pulse (common drive waveform) in the second embodiment of the present invention will be described with reference to FIG.
Here, the idle ejection drive signal is composed of nine pulses of drive pulses P11 to P19. In each of the drive pulses P11 to P19, droplet discharge by the drive pulse is performed at a timing that resonates with the pressure vibration of the liquid chamber 106 generated by performing droplet discharge of the empty droplet by the drive pulse before the drive pulse. The timing is set.

  Also, here, the first to third drive pulses P11 to P13 have waveform elements (in this case, waves) so that the empty ejection droplets ejected by these three drive pulses merge (merge) during the flight. High value) is set.

  Furthermore, the fourth and fifth drive pulses P14 and P15 set waveform elements (here, crest values) so that the empty ejected droplets ejected by these two drive pulses merge (merge) during flight. is doing. Similarly, the sixth and seventh drive pulses P16 and P17 have waveform elements (here, crest values) so that the empty ejected droplets ejected by these two drive pulses merge (merge) during the flight. It is set. Similarly, the eighth and ninth (last) drive pulses P18 and P19 have waveform elements (in this case, waves) so that the empty ejected droplets ejected by these two drive pulses merge (merge) during the flight. High value) is set.

  As a result, by applying the drive pulses P11 to P19, nine empty ejection droplets are ejected, merge during flight, and then fly as four droplets.

  At this time, the droplet merged with the empty ejection droplets ejected by the drive pulses P11 to P13 has a flight speed of 10 m / s or more, and each of the merged droplets that subsequently fly has a slow flight speed. As a result, the droplets merged by the empty ejection droplets ejected by the drive pulses P18 and P19 have a flying speed of 8 m / s or less.

  That is, here, the plurality of empty ejection droplets includes a plurality of merged droplets during the flight, and the plurality of merged droplets have a drop speed that decreases stepwise. As a result, no satellite-like microdroplets are generated between the merged drops, and no satellite-like microdroplets are generated after the last merged drop.

Next, the idle ejection drive pulse (common drive waveform) in the third embodiment of the present invention will be described with reference to FIG.
Here, the idle ejection drive signal is composed of 6 pulses of drive pulses P21 to P25. The drive pulses P21 to P24 are timings at which droplet ejection by the drive pulse is performed at a timing that resonates with the pressure vibration of the liquid chamber 106 that is generated by performing droplet ejection of the empty ejection droplet by the drive pulse before the drive pulse. Is set. Further, the drive pulse P25 is set to a timing at which droplet ejection by the drive pulse is performed at a timing that does not resonate with the pressure vibration of the liquid chamber 106 generated by performing droplet ejection of the empty ejection droplets by the drive pulses P21 to P24. Yes.

  Also, here, the ejection speed of the empty ejection droplets by the drive pulse P21 is 10 m / s or more, and the ejection speed of the empty ejection droplets ejected by the drive pulses P21 to P24 gradually decreases, and the drive pulse P24 The discharge speed of the empty discharged droplets discharged by the above is 8 m / s or less. Further, the drive pulse P5 also causes the discharge speed of the discharged empty droplets to be 8 m / s or less, and the wave height value is increased by the amount that is out of resonance.

  As a result, no satellite-like microdroplet is generated between the empty ejection droplets by the drive pulses P21 to P25, and no satellite-like microdroplet is generated after the last empty ejection droplet. It can be discharged.

  Further, by removing the last drive pulse P25 from the continuous resonance (continuous fluid chamber pressure fluctuation) caused by continuous droplet ejection by the previous drive pulses P21 to P24, the influence of the previous drive pulses P21 to 24 can be reduced. It is possible to reduce the independence and improve the ejection stability with respect to the thickened ink in the nozzle as compared with the case of continuous resonance (when the drive pulse P25 is resonated with the previous pressure vibration).

Next, the relationship between the member that receives the idle ejection droplets and the idle ejection cycle will be described with reference to FIG. FIG. 10 is an explanatory perspective view of the idle discharge receiver.
The empty discharge receiver 88 is a semi-sealed container having two openings 89. When the empty discharge droplets are discharged from the recording head 34 to such a semi-sealed empty discharge receiver, the droplets are discharged. The phenomenon that the air flow is blown back from the opening 89 due to the influence of the air flow due to the discharge of the air occurs.

  Similarly, when idle ejection is performed from the recording head 34 to the cap 82a, the influence of the airflow due to the ejection is greatly influenced by the cap shape, and an airflow from the cap 82a toward the outside of the cap 82a is generated.

  For this reason, in the case of a previously ejected droplet in which a satellite-like micro droplet is generated, the micro droplet is scattered as a mist on the air stream. On the other hand, in the empty ejection droplets according to the above-described embodiment, satellite-like micro droplets are not generated even if the ejection cycle is lengthened, so that the air flow caused by the empty ejection droplets can be suppressed. In addition, the discharge cycle at that time is set to four times or more of the waveform time by a plurality of pulses in one discharge cycle, so that the generation of air current is reduced to a quarter or less than when the discharge cycle is equal to the waveform time. Can be suppressed. Further, since the longer one discharge cycle is, the more the influence of the air flow caused by the empty discharge droplets can be suppressed, the discharge cycle can be set to an arbitrary one in consideration of the productivity of the printed matter.

  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.

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. It is explanatory drawing which shows the idle discharge drive pulse in 1st Embodiment of this invention. It is explanatory drawing which shows the idle discharge drive pulse in 2nd Embodiment of this invention. It is explanatory drawing which shows the idle discharge drive pulse in 3rd Embodiment of this invention. It is a perspective explanatory view of an empty discharge receiver for explaining a relationship between a member that receives empty discharge droplets and an empty discharge cycle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Ink cartridge 33 ... Carriage 34, 34a, 34b ... Recording head (liquid discharge head)
81: Maintenance / recovery mechanism 82a ... Cap 88 ... Empty discharge receptacle 89 ... Opening 508 ... Print control unit

Claims (5)

A recording head having nozzles for discharging droplets;
Means for performing an empty discharge operation for continuously discharging a plurality of empty discharge droplets that do not contribute to image formation from the recording head,
The droplet speed of the empty discharge droplet to be discharged at the end of the plurality of empty discharge droplets is a droplet velocity at which no satellite is generated, and is lower than the droplet velocity of the empty discharge droplet to be discharged first. An image forming apparatus.   The image forming apparatus according to claim 1, wherein drop speeds of the plurality of empty ejection drops are decreased stepwise.   2. The plurality of empty ejection droplets include droplets that become a plurality of merged droplets during a flight, and the plurality of merged droplets have a drop speed that decreases stepwise. Image forming apparatus.   The plurality of empty ejection droplets include a droplet ejected at a timing resonating with pressure vibration of a liquid chamber to which the nozzle of the recording head communicates, and a droplet ejected at a timing not resonating with the pressure vibration, 2. The image forming apparatus according to claim 1, wherein the last ejected empty ejected droplet is a droplet ejected at a timing not resonating with the pressure vibration. A recording head having nozzles for discharging droplets;
Means for performing an empty discharge operation for continuously discharging a plurality of empty discharge droplets that do not contribute to image formation from the recording head,
The image forming apparatus according to claim 1, wherein a droplet speed of an empty discharge droplet to be discharged last among the plurality of empty discharge droplets is lower than a droplet speed of an empty discharge droplet to be discharged first.

Images