JP2010115913A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem the impossibility of efficient removal of foreign matters such as paper duct, under the condition that the ink meniscus of a nozzle is stably retained in the case of a recovering action performed by applying a sucking force and extruding force under the driving of a sucking means and also the driving of an actuator to ink near a nozzle hole or the like. <P>SOLUTION: The image forming device performs a first action, which generates a pressure change in a liquid chamber 106 by applying a maintenance driving waveform having a peak value V1 to the pressure generating means of a recording head 34 while ink is sucked from a nozzle 104 by capping the nozzle face of the recording head 34 with a cap 82a, and a second action, which generates a pressure change, which is smaller than the pressure change generated by the first action by applying a maintenance driving waveform having a peak value V2, which is smaller than the peak value V1 in the first action after the first action. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to a recovery 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.

  When image formation is repeated in such an image forming apparatus, paper dust or the like may adhere to the nozzles of the recording head, resulting in ejection failure or ejection failure due to nozzle clogging. Even if a recovery operation such as nozzle suction by the maintenance recovery mechanism is performed on the recording head to which paper dust or the like is attached, it is difficult to remove the paper dust.

  Therefore, as described in Patent Documents 1 to 3, the actuator of the recording head (pressure generating means) is driven while the suction means is driven so that the suction force and the pushing force are applied to the ink or the like in the vicinity of the nozzle holes. It is known to perform recovery operations.

JP 2007-136989 A JP 2001-260393 A JP 2006-315200 A

  However, when a recovery operation is performed in which the suction force and the pushing force are applied to the ink in the vicinity of the nozzle hole by driving the actuator while driving the suction means, the nozzle is generated when the pressure generated by the actuator during suction is large. The ink meniscus cannot be stably held, and if the pressure generated by the actuator is low, the efficiency of removing foreign matters such as paper dust is reduced.

  The present invention has been made in view of the above problems, and an object of the present invention is to enable efficient removal of foreign matters such as paper dust while stably holding an ink meniscus.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A recording head having a nozzle for ejecting ink droplets, a liquid chamber in which the nozzle communicates, and a pressure generating means for generating pressure in the liquid chamber;
A maintenance and recovery mechanism for capping the nozzle surface of the recording head with a cap member and sucking ink from the nozzle;
A first operation for driving the pressure generating means of the recording head to cause a pressure change in the liquid chamber while capping by the cap member and sucking ink from the nozzle; and And a recovery operation control means for performing a second operation that causes a pressure change that is less than or equal to the pressure change in the first operation later.

  Here, a first recovery mode in which both the first operation and the second operation are performed, and a second recovery in which at least one of the first operation and the second operation is performed. And a mode.

  Further, the second operation may be performed after the first operation is performed a plurality of times.

  In addition, the operation of performing the second operation after performing the first operation can be configured to be performed a plurality of times.

  Further, the number of driving times of the pressure generating means in the second operation may be less than the number of driving times of the pressure generating means in the first operation.

  Further, the pressure change in the first operation and the second operation can be reduced stepwise.

  Further, in the first operation and the second operation, a driving waveform having substantially the same period as the natural vibration period in the liquid chamber of the recording head can be applied to the pressure generating unit.

  Further, the first drive waveform and the second drive waveform may be different from the drive waveform used in image formation.

  Further, it is possible to select from the first recovery mode and the second recovery mode according to the number of printed sheets.

  According to the image forming apparatus of the present invention, the first operation of driving the pressure generating means of the recording head to cause a pressure change in the liquid chamber while capping with the cap member and sucking ink from the nozzles. Since the second operation for generating a pressure change equal to or lower than the pressure change in the first operation is performed after the first operation, foreign matters such as paper dust are efficiently removed while the ink meniscus is stably held. become able to.

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. This nozzle plate 103 has a water repellent layer formed on the outermost surface through a required layer on the surface of a nozzle forming member made of a metal member, and the outermost surface becomes a nozzle surface 103a capped by a cap 82a.

  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, the maintenance / recovery mechanism 81 in this image forming apparatus will be described with reference to FIG. FIG. 5 is a schematic schematic configuration diagram of the maintenance and recovery mechanism.
In the maintenance / recovery mechanism 81, the caps 82 a and 82 b held by the cap holder 212, the wiper member 83 including an elastic body, and the wiper cleaner 86 are held up and down (movable up and down) by the maintenance device frame 211. Has been.

  A cylindrical empty discharge receiver 84 is disposed between the wiper member 83 and the suction cap 82a. The upper end of the empty discharge receiver 84 on the wiper member 83 side scrapes ink adhering to the wiper member 83. A wiper cleaner portion 85 to be dropped is formed. When cleaning the wiper member 83, the wiper member 83 is lowered while the wiper member 83 is pressed against the wiper cleaner portion 85 by the wiper cleaner 86, so that the ink adhering to the wiper member 83 is scraped off to the empty ejection receiver 84 side. .

  Further, a tubing pump (suction pump) 220 as a suction means is connected to the cap 82a closest to the printing area via a flexible tube 219, and only the cap 82a is suctioned (recovered) and moisturized (hereinafter referred to as the cap 82a). It is simply referred to as “suction cap”), and the cap 82b is simply a moisture retention cap. Therefore, when performing the recovery operation of the recording head 34, the recording head 34 that performs the recovery operation is selectively moved to a position where it can be capped by the suction cap 82a.

  A cam shaft 221 that is rotatably supported by the frame 211 is disposed below the caps 82a and 82b, the wiper member 83, and the like, and a cap cam 222 for raising and lowering the cap holder 212 is disposed on the cam shaft 221. A wiper cam 224 for raising and lowering the wiper member 83, a roller 226 as a rotating body to which liquid droplets idled in the idle discharge receptacle 84 are applied, a cleaner cam 228 for swinging the wiper cleaner 86, and a carriage lock Carriage lock cams 229 for moving up and down 87 are provided.

  In order to rotationally drive the suction pump 220 and the cam shaft 221, the rotation of the motor 231 is meshed with the motor gear 232 provided on the motor shaft 231 a and the pump gear 233 provided on the pump shaft 220 a of the suction pump 220 is further engaged. An intermediate gear 236 with a one-way clutch 237 is meshed with an intermediate gear 234 integral with the intermediate gear 233, and the intermediate gear 238 coaxial with the intermediate gear 236 is fixed to the camshaft 221 via the intermediate gear 239. The cam gear 240 is engaged. The intermediate shaft 241 that is the rotation shaft of the intermediate gears 236 and 238 with the clutch 237 is rotatably held by the frame 211.

  In this maintenance / recovery mechanism 81, when removing ink and impurities adhering to the surface (nozzle surface) where the nozzles of the recording head 34 are formed, the motor 231 is driven and the wiper blade 83 is raised via the wiper cam 224. In this state, by moving the carriage 33 in the main scanning direction, the wiper blade 83 wipes the nozzle surface of the recording head 34 to wipe away impurities and the like.

  Further, if the nozzles of the recording head 34 are left exposed to the outside air, the ink in the inside dries and thickens and adheres, and the ink ejection performance is deteriorated. To prevent this, the recording head 34 is prevented. When the nozzle surface is covered with the cap 82, the motor 231 is rotated, the cap 82 is raised via the cap cam 213, and the nozzle surface of the recording head 34 is capped.

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 temporarily stores a CPU 511 that also serves as a means for controlling the recovery 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 storing, rewritable nonvolatile memory 504 for holding data even while the power of the apparatus is shut off, image processing for performing various signal processing and rearrangement on image data, and other control of the entire apparatus And an ASIC 505 for processing input / output signals.

  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 and moves the conveyor belt 51, a motor drive unit 510 that drives the maintenance / recovery motor 231 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 temperature / humidity sensor (environmental sensor) for detecting the temperature and humidity in the apparatus, a sensor for monitoring the voltage of the charging belt, and an interface for detecting opening and closing of the cover. There are lock switches and the like, and 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 common drive waveform (drive waveform for image formation) composed of a plurality of drive pulses (drive signals) within one printing cycle at the time of image formation, and maintains and recovers it. A drive waveform generation unit 701 that generates and outputs a common drive waveform (maintenance drive waveform) composed of sinusoidal drive signals within one drive cycle during operation (maintenance operation), and a 2-bit corresponding to a print image A data transfer unit 702 that outputs image data (gradation signals 0 and 1), a clock signal, a latch signal (LAT), and droplet control signals M0 to M3 is provided.

  The droplet control signal is a 2-bit signal that instructs each droplet to open and close the analog switch 715 that is a switch unit 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 to ON), and state transition 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 for level conversion to an analog switch 716 and an analog switch 716 that is turned on / off (opened / closed) by the output of the decoder 713 provided via the level shifter 714 are provided.

  The analog switch 715 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.

  Here, when performing a maintenance operation for maintaining and recovering the performance of the recording head 34, the CPU 501 of the control unit 500 controls the drive of the maintenance / recovery mechanism 81 and performs a maintenance drive waveform for the drive waveform generation unit 701. And the image data for driving each pressure generating means (actuator: piezoelectric element 121 in this example) of the recording head 34 is given to the data transfer unit 702, so that the maintenance driving waveform of the recording head 34 is controlled. Recovery operation control for driving each piezoelectric element 121 to cause a pressure change in the liquid chamber 106 is performed.

Next, the recovery operation of the recording head in this image forming apparatus will be described with reference to FIG.
In the recovery operation, as described above, by operating the suction pump 231 in a state where the nozzle surface 103a of the recording head 34 is capped by the suction cap 82a, ink is sucked from the nozzle 104 of the recording head 34, and the nozzle surface 103a. The ink adhering to the recording head 34 is wiped by the wiper blade 83, and the ink in the suction cap 82a is sucked and discharged, so that the ejection performance of the nozzle 104 of the recording head 34 is maintained and recovered.

  Here, as shown in FIG. 8A, while the nozzle surface 31a of the recording head 31 is capped with the suction cap 82a, the suction pump 220 is operated to perform the head suction for sucking ink. As shown in FIG. 4B, a maintenance drive waveform is applied to the piezoelectric element 121 which is a pressure generating means of the recording head 31 to change the pressure in the liquid chamber 106 (the volume in the liquid chamber is expanded or contracted). And the operation of ejecting droplets from the nozzle 104 is also performed.

  That is, in the recovery operation, the first operation for driving the pressure generating means (piezoelectric element 121) of the recording head 34 to cause a pressure change in the liquid chamber 106 during the suction, and the first operation after the first operation. The second operation for causing a pressure change equal to or less than the pressure change in the first operation is performed.

  Here, in the first operation, the recording head 34 is driven by giving a maintenance drive waveform having a peak value V1 to discharge droplets. In the second operation, the recording head 34 is driven to eject droplets by applying a maintenance drive waveform having a peak value V2 lower than the peak value V1. By changing the peak value V2 of the maintenance drive waveform of the second operation to be lower than the peak value V1 of the maintenance drive waveform of the first operation, the pressure change in the liquid chamber caused by the second operation is the first operation. It becomes below the pressure change in.

  In this case, in the first operation, a condition for applying a drive waveform to the piezoelectric element 121 of the recording head 34, for example, an elapsed time (waiting time) n1 (ms) from the start of head suction shown in FIG. Drive number (number of droplets to be ejected n2 (droplets)), elapsed time n3 (ms) from the previous drive, and the total number of drive times N (times) can be predetermined or included in the sensor group 515. It can also be determined according to the environmental condition detected based on the detection signal from the environmental sensor (temperature / humidity sensor) or the number of printed sheets.

  The same applies to the conditions for applying the drive waveform to the piezoelectric element 121 of the recording head 34 in the second operation. For example, the elapsed time (waiting time) n4 (ms) from the start of head suction shown in FIG. The number of times of driving once (the number of droplets to be ejected n5 (droplets)), the elapsed time from the previous driving, and the total number of times of driving N can be determined in advance, or an environmental sensor ( It can also be determined according to the environmental condition detected based on the detection signal from the temperature / humidity sensor) or the number of printed sheets. In this example, since the second operation is for stabilizing the meniscus, the total number of driving times N is one.

Here, the driving waveform for maintenance will be described with reference to FIG.
As the maintenance drive waveform, a sinusoidal drive waveform is used as shown in FIG. The period of the maintenance drive waveform is substantially the same as the natural vibration period Tc in the liquid chamber 106 of the recording head 34. As a result, the pressure change in the liquid chamber 106 of the recording head 34 can be substantially maximized, the pressure applied to the nozzle 104 is increased, and recovery can be performed with a high recovery rate.

  Since the main purpose is to remove paper dust in the first operation and the main purpose is to stabilize the meniscus in the second operation, the peak value V1 of the maintenance drive waveform for the first operation. And the peak value V2 of the maintenance drive waveform for the second operation, as described above, the peak value V2 of the maintenance drive waveform for the second operation is the wave of the maintenance drive waveform for the first operation. It is lower (smaller) than the high value V1.

  Thus, unlike the printing (image forming) driving waveform that is normally used for printing, the driving waveform that easily resonates with the natural vibration of the liquid chamber 106 is used as the maintenance driving waveform. In particular, by using a sinusoidal drive waveform, the pressure in the liquid chamber 106 can be maximized, and recovery (removal of paper dust) can be performed with a high recovery rate.

  Unlike the sine wave, the printing drive waveform used for normal printing is a stroke that causes the pressure generating chamber (liquid chamber 106) to expand and contract as shown in FIG. 10 to discharge ink from the vicinity of the center of the meniscus. The droplets are ejected by using a pushing method in which the method and the pressure generating chamber are contracted without being expanded and ink is ejected from the entire nozzle 104.

  In this case, as described above, by using a sine wave as the maintenance drive waveform, the period of the maintenance drive waveform can be easily adjusted to the natural vibration period in the liquid chamber (pressure generation chamber), and the rectangular wave The load on the driver IC or the like is reduced compared to a drive waveform having a sudden voltage change such as.

Next, the timing for applying the maintenance drive waveform will be described. As shown in FIG. 11, the maintenance drive waveform is applied within a section (time) in which the pressure (negative pressure) in the cap 82a is 50% or more of the maximum pressure. I am doing so.
FIG. 11 shows an example of the measurement result of the negative pressure change of the cap 82a when the suction pump 211 is operated after capping with the cap 82a. In this example, the negative pressure is about −6 [kPa] or more. The maintenance drive waveform is applied during the time (within the shaded area in FIG. 11).

  If driving is performed in a state where the pressure (negative pressure) in the cap is low, bubbles are likely to be trapped, and the cleaning performance may be deteriorated.

  Further, regarding the maintenance drive waveform, since the ink viscosity changes according to the environmental conditions, it is preferable to vary the peak value (voltage value) according to the environmental conditions. For example, as shown in FIG. 12, a room temperature driving waveform with a relatively high peak value, a low temperature driving waveform with a relatively high peak value, and a high temperature with a relatively low peak value, depending on environmental conditions. A high drive waveform for low temperature is applied at a low temperature when the ink viscosity is relatively high, and a high drive waveform for low temperature is applied at a high temperature when the ink viscosity is relatively low.

  Thereby, even when the ink viscosity changes depending on the environment, it is possible to perform an optimal recovery operation according to the viscosity by changing the peak value of the drive waveform. If the voltage of the drive waveform is too low, the effect of recovery is reduced. Conversely, if the voltage is too high, bubbles are easily trapped and the cleaning performance is deteriorated. Therefore, a drive waveform corresponding to the viscosity is applied.

  As described above, in the recovery operation, during the suction, a maintenance drive waveform is given in the first operation to cause a pressure change in the liquid chamber 106 to discharge the liquid droplets, thereby externally causing paper dust or the like. Even when such foreign matter is clogged in the hole of the nozzle 104 of the recording head 34 and ejection failure or ejection failure occurs, the paper powder can be discharged to the cap 82a by the pressure change in the liquid chamber 106 and removed.

  That is, by changing the pressure in the liquid chamber of the recording head in the first operation in parallel with the head suction, the pressure changes more than simply applying a pressure (the pressure that does not change) that contracts the volume in the liquid chamber. Pressure can be applied to external foreign matter such as paper dust clogged in the nozzle, and foreign matter such as paper dust clogged in the nozzle can be reliably removed and stable. Thus, the high ejection quality can be obtained and high image quality can be maintained.

  In the second operation, a maintenance drive waveform having a smaller peak value than the maintenance drive waveform given in the first operation is applied to cause a pressure change in the liquid chamber 106, so that the nozzle operation is performed in the first operation. Even if the ink meniscus becomes unstable, the meniscus is made stable.

  Here, for example, the maintenance driving waveform used in the second operation is a driving waveform in which the crest value gradually decreases (the pressure generated in the liquid chamber 106 is decreased stepwise) as shown in FIG. Thus, the meniscus can be made more stable. In this case, the maintenance drive waveform used in the first operation can similarly be a drive waveform in which the crest value decreases stepwise (the pressure generated in the liquid chamber 106 decreases stepwise). Thus, the meniscus can be further stabilized.

  In this way, after performing suction a plurality of times and performing the first operation with a drive waveform having a high peak value during suction, the second operation is performed with a drive waveform having a small peak value during suction. Thus, even when the meniscus is unstable in the first operation, the meniscus can be adjusted to a stable state by performing the second operation. Further, foreign matters such as paper dust that could not be completely removed by the first operation can be removed by the second operation.

  In this case, since there is not much foreign matter such as paper dust entering the nozzle frequently, the first recovery mode in which both the first operation and the second operation described above are performed is used as the recovery operation mode. And the second recovery mode that performs only the second operation described above, the second recovery mode is performed as a recovery mode that is frequently used, and the recovery is difficult in the first recovery operation mode. Preferably, the recovery operation mode 1 is implemented.

Therefore, an example of control of the recovery operation by the control unit will be described with reference to a flowchart shown in FIG.
In this example, as described above, as the recovery operation mode, the first recovery mode in which both the first operation and the second operation are performed, and the second recovery mode in which only the second operation is performed are performed. I have.

  First, when the recovery operation is started, the temperature / humidity sensor detects the temperature / humidity and selects the drive waveform according to the environmental conditions as described above, and then supplies ink to the sub tank 35 to supply the required amount of ink in the sub tank 35. To.

  Then, it is determined whether or not the first recovery mode is selected. When the first recovery mode is selected, the suction operation with the second operation is performed after the suction operation with the first operation is performed. When the first recovery mode is not selected, the suction operation with the second operation is performed without performing the suction operation with the first operation.

  Thereafter, the nozzle surface of the recording head 34 is wiped by the wiper blade 83, and the recovery operation is terminated by performing idle ejection, and the nozzle surface of the recording head 34 is capped by the cap 82, and the standby state is entered.

Next, another example of the recovery operation control by the control unit will be described with reference to the flowchart shown in FIG.
In this example, it is determined whether or not the number of printed sheets is equal to or greater than a predetermined number. When the number of printed sheets is equal to or greater than the predetermined number, a first operation that performs a suction operation with a first operation and then performs a suction operation with a second operation is performed. The recovery mode is performed, and when the number of printed sheets is not equal to or greater than the predetermined number, the second recovery mode in which the suction operation with the second operation is performed without performing the suction operation with the first operation is performed.

  In other words, foreign matter such as paper dust is more likely to block the nozzle hole as the number of printed sheets increases, so the number of printed sheets is stored, and if the number of printed sheets is less than a predetermined number, the first recovery is performed. The operation mode is performed, and if the number is greater than or equal to the predetermined number, the second recovery operation mode is performed.

  In the above embodiment, the printer configuration has been described as the image forming apparatus according to the present invention. However, the present invention is not limited to this, and can be applied to an image forming apparatus such as a printer / fax / copier multifunction machine. Further, the present invention can be applied to an image forming apparatus using a recording liquid or a fixing processing liquid that is a liquid other than ink.

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. 2 is a schematic explanatory diagram of a maintenance / recovery mechanism of the image forming apparatus. FIG. FIG. 2 is a block explanatory diagram illustrating an overview of a control unit of the image forming apparatus. 2 is a block diagram illustrating an example of a print control unit and a head drive unit of the control unit. FIG. It is explanatory drawing with which it uses for description of recovery operation | movement in this invention. It is explanatory drawing which shows an example of the drive waveform for a maintenance. It is explanatory drawing which shows an example of the drive waveform for printing. It is explanatory drawing with which it uses for description of the relationship between the negative pressure change in a cap, and the timing which uses the drive waveform for a maintenance. It is explanatory drawing explaining the example with respect to the environmental temperature of the drive waveform for a maintenance. It is explanatory drawing explaining the other example of the drive waveform for a maintenance. It is a flowchart explaining an example of recovery operation control. It is a flowchart explaining an example of recovery operation control.

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 508 ... Print controller 701 ... Drive waveform generator

Claims (9)

A recording head having a nozzle for ejecting ink droplets, a liquid chamber in which the nozzle communicates, and a pressure generating means for generating pressure in the liquid chamber;
A maintenance and recovery mechanism for capping the nozzle surface of the recording head with a cap member and sucking ink from the nozzle;
A first operation for driving the pressure generating means of the recording head to cause a pressure change in the liquid chamber while capping by the cap member and sucking ink from the nozzle; and An image forming apparatus comprising: a recovery operation control unit that performs a second operation that causes a pressure change that is less than or equal to the pressure change in the first operation later. A first recovery mode in which both the first operation and the second operation are performed; and a second recovery mode in which at least one of the first operation and the second operation is performed. The image forming apparatus according to claim 1, further comprising:   The image forming apparatus according to claim 1, wherein the second operation is performed after the first operation is performed a plurality of times.   The image forming apparatus according to claim 1, wherein the operation of performing the second operation is performed a plurality of times after the first operation is performed.   5. The image forming apparatus according to claim 1, wherein the number of driving times of the pressure generating unit in the second operation is smaller than the number of driving times of the pressure generating unit in the first operation.   6. The image forming apparatus according to claim 1, wherein a pressure change in the first operation and the second operation is reduced stepwise.   7. The pressure generating means according to claim 1, wherein in the first operation and the second operation, a driving waveform having substantially the same period as the natural vibration period in the liquid chamber of the recording head is applied to the pressure generating means. The image forming apparatus described.   The image forming apparatus according to claim 1, wherein the first drive waveform and the second drive waveform are different from drive waveforms used in image formation.   9. The image forming apparatus according to claim 1, wherein the image forming apparatus selects one of the first recovery mode and the second recovery mode according to the number of printed sheets.

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