JP2007136989A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that foreign matter such as paper dust adhering to nozzles cannot be unerringly removed only by cleaning actions to suck an ink from a head. <P>SOLUTION: The image forming device performs an idle discharge to discharge liquid droplets from the nozzles 104 by causing a pressure variation (expansion or contraction of the internal capacity of a liquid chamber) in a liquid chamber 106 by providing a maintenance driving waveform to the piezoelectric element 121 of a recording head 31 while performing head suction to suck an ink by operating a suction pump 211 with the nozzle surface 31a of the recording head 31 capped by a sucking cap 82a. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and a recording head recovery method, and more particularly to an image forming apparatus that discharges a recording liquid to form an image and a recording head recovery method.

  As an image forming apparatus such as a printer, a facsimile, a copying apparatus, and a multifunction machine of these, for example, an ink jet recording apparatus is known. The ink jet recording apparatus is a recording medium such as recording paper (hereinafter referred to as “paper”) from the recording head, but the material is not limited to paper, and is also referred to as recording medium, transfer paper, transfer material, recording material, and the like. In this case, recording (image formation, printing, printing, printing, etc. are synonymous) is performed by ejecting ink droplets, which are droplets of recording liquid.

An image forming apparatus that forms an image by ejecting such recording liquid droplets requires a maintenance and recovery operation for maintaining and recovering the performance of the recording head since the recording droplets are ejected. Therefore, in order to prevent thickening and sticking of the recording liquid in the vicinity of the nozzle hole due to natural evaporation of the ink, the recording liquid is discharged to prevent the recording liquid from being ejected due to a cap function that is covered with a highly-sealing cap member and bubbles generated in the nozzle. And a recovery recovery function that sucks and discharges the recording liquid from the nozzle of the head through the cap function, and wipes the residual recording liquid that adheres to the nozzle surface and causes the droplet flight state to change. For example, a wiping function for wiping off, and an empty discharge (preliminary discharge) function for discharging liquid droplets that do not contribute to image formation.
JP 2005-144939 A

In such a maintenance and recovery operation, as described in Patent Document 2, the outer opening of the nozzle hole of the inkjet head is covered with a cap member, and a suction means for sucking ink or an ink lump in the vicinity of the nozzle hole is operated. It is known that the actuator is deformed when the ink is pushed to push out the ink, and the suction force and the pushing force are applied to the ink in the vicinity of the nozzle hole.
JP 2001-260393 A

  By the way, when image formation is repeated in the image forming apparatus, paper dust or the like may adhere to the nozzles of the recording head and cause 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 Document 2, it is conceivable to apply a recovery operation in which the suction unit is driven and the actuator is also driven to cause the suction force and the pushing force to act on the ink or the like in the vicinity of the nozzle hole. Just by deforming the actuator so as to shrink the volume of the liquid chamber as in Patent Document 2, it is not possible to exert sufficient removal pressure on foreign matters such as paper dust other than ink clogged in the nozzle, There is a problem that it is difficult to remove foreign matters such as paper dust.

  The present invention has been made in view of the above problems, and an image forming apparatus capable of performing image formation by stable droplet discharge by reliably removing foreign matters such as paper dust in the nozzle and paper in the nozzle An object of the present invention is to provide a recording head recovery method for reliably removing foreign matters such as powder.

  In order to solve the above-described problems, the image forming apparatus according to the present invention drives the pressure generating means of the recording head to cap the pressure change in the liquid chamber while capping the cap member and sucking the recording liquid from the nozzle. It was set as the structure provided with the means to perform the maintenance operation | movement to produce.

  Here, in the maintenance operation, it is preferable to apply a drive waveform having substantially the same period as the natural vibration period in the liquid chamber of the recording head to the pressure generating means. Moreover, it is preferable that the time for applying the drive waveform is during the time when the pressure in the cap member is 50% or more of the maximum pressure. Moreover, it is preferable that the peak value of a drive waveform changes according to environmental conditions. The drive waveform used in the maintenance operation is preferably different from the drive waveform used in image formation. The drive waveform is preferably a sine wave. Moreover, it is preferable that the drive frequency of a drive waveform is 10 kHz or more. Further, a maintenance operation can be performed according to the number of printed sheets.

  The recording head recovery method according to the present invention is configured to drive the recording head to cause a pressure change in the liquid chamber while the recording liquid is sucked from the nozzle by capping with the cap member.

  According to the image forming apparatus and the recording head recovery method of the present invention, while the cap is capped and the recording liquid is sucked from the nozzle, the pressure generating means of the recording head is driven to change the pressure in the liquid chamber. This can provide sufficient pressure to remove foreign matter such as paper dust adhering to the nozzle of the recording head, and reliably remove foreign matter such as paper dust in the nozzle for stable droplet ejection. Image formation can be performed.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an explanatory perspective view of the image forming apparatus as an example of the image forming apparatus according to the present invention as viewed from the front side.
The image forming apparatus includes an apparatus main body 1, a paper feed tray 2 for loading paper loaded in the apparatus main body 1, and a sheet on which an image is recorded (formed) by being detachably mounted on the apparatus main body 1. A paper discharge tray 3 for stocking is provided. Furthermore, a cartridge loading for loading an ink cartridge that protrudes from the front surface to the front side of the apparatus main body 1 and is lower than the upper surface is provided at one end side of the front surface of the apparatus main body 1 (side of the paper supply / discharge tray section). The cartridge loading unit 4 has an operation / display unit 5 provided with operation buttons and a display.

  The cartridge loading unit 4 includes a plurality of recording liquid cartridges that contain recording liquids (inks) of different colors, for example, black (K) ink, cyan (C) ink, magenta (M) ink, and yellow (Y) ink. Ink cartridges 10k, 10c, 10m, and 10y (referred to as “ink cartridge 10” when colors are not distinguished) are inserted from the front side to the rear side of the apparatus main body 1 and can be loaded. A front cover (cartridge cover) 6 that is opened when the ink cartridge 10 is attached or detached is provided on the front side of the unit 4 so as to be openable and closable.

  Further, the operation / display unit 5 has the remaining amounts of the ink cartridges 10k, 10c, 10m, and 10y of each color at the arrangement positions corresponding to the mounting positions (arrangement positions) of the ink cartridges 10k, 10c, 10m, and 10y of the respective colors. The remaining amount display portions 11k, 11c, 11m, and 11y for each color for displaying the near end and the end are arranged. Further, the operation / display unit 5 is also provided with a power button 12, a paper feed / print resume button 13, and a cancel button 14.

Next, the mechanism of this image forming apparatus will be described with reference to FIGS. FIG. 2 is a schematic configuration diagram for explaining the overall configuration of the mechanism unit, and FIG.
A guide rod 21, which is a guide member placed horizontally between left and right side plates (not shown), and a stay 22 hold the carriage 23 slidably in the main scanning direction, and is driven between the driving pulley 25 and the driven pulley 26 by the main scanning motor 24. 3 moves and scans in the direction indicated by the arrow (carriage scanning direction: main scanning direction) in FIG.

  The carriage 23 has recording heads 31k, 31c, 31m, and 31y (distinguishable) composed of droplet ejection heads that eject ink droplets of yellow (Y), cyan (C), magenta (M), and black (Bk). If not, it is referred to as “recording head 31”). A plurality of ink ejection openings are arranged in a direction crossing the main scanning direction, and the ink droplet ejection direction is directed downward.

  As an ink jet head constituting the recording head 31, a piezoelectric actuator such as a piezoelectric element, a thermal actuator that uses a phase change caused by film boiling of a liquid using an electrothermal transducer such as a heating resistor, and a metal phase change caused by a temperature change. It is possible to use a shape memory alloy actuator to be used, an electrostatic actuator using an electrostatic force, or the like provided as pressure generating means for generating a pressure for discharging a droplet. In addition, the inkjet head has a configuration in which a plurality of nozzle rows are arranged and a plurality of nozzle rows are arranged, and droplets of the same color are ejected from each nozzle row. Also good.

  The carriage 23 is equipped with a sub tank 32 for each color for supplying each color ink to the recording head 31. Each color sub-tank 32 is supplementarily supplied with ink of each color from the ink cartridge 10 of each color mounted in the cartridge loading unit 4 via the ink supply tube of each color.

  On the other hand, as a sheet feeding unit that is a feeding unit for feeding the sheets 42 stacked on the sheet stacking unit (pressure plate) 41 of the sheet feeding tray 2, the sheets 42 are separated and fed one by one from the sheet stacking unit 41. A half paddle (feed roller) 43 and a separation pad 44 made of a material having a large friction coefficient are provided opposite to the half-moon roller (sheet feed roller) 43, and the separation pad 44 is urged toward the sheet feed roller 43 side.

  In order to feed the sheet 42 fed from the sheet feeding unit to the lower side of the recording head 31, a guide member 45 for guiding the sheet 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 31.

  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). This transport belt 51 is, for example, a surface layer that is a sheet adsorbing surface formed of a pure resin material having a thickness of about 40 μm that is not subjected to resistance control, such as ETFE pure material, and resistance control by carbon with the same material as this surface layer. And a back layer (medium resistance layer, ground layer).

  A charging roller 56 is provided as charging means for charging the surface of the conveyor belt 51. The charging roller 56 is disposed so as to come into contact with the surface layer of the conveyor belt 51 and to be rotated by the rotation of the conveyor belt 51, and applies a predetermined pressing force to both ends of the shaft as a pressing force. In addition, a guide member 57 is disposed on the back side of the conveyance belt 51 so as to correspond to a printing area by the recording head 31.

  The conveyance belt 51 rotates in the belt conveyance direction (sub-scanning direction) in FIG. 3 when the conveyance roller 52 is rotationally driven by the sub-scanning motor 58 via the drive belt 59 and the pulley 60.

  Further, as a paper discharge unit for discharging the paper 42 recorded by the recording head 31, a separation claw 61 for separating the paper 42 from the conveyance belt 51, a paper discharge roller 62, and a paper discharge roller 63 are provided. The paper discharge tray 3 is provided 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, as shown in FIG. 3, a maintenance / recovery mechanism 81 including a recovery means for maintaining and recovering the nozzle state of the recording head 31 is arranged in the non-printing area on one side of the carriage 23 in the scanning direction. Yes.

  The maintenance / recovery mechanism 81 includes cap members (hereinafter referred to as “caps”) 82a to 82d (hereinafter referred to as “caps 82” when not distinguished from each other) for capping the nozzle surfaces of the recording head 31, and nozzle surfaces. A wiper blade 83 that is a blade member for wiping the ink, and an empty discharge receiver 84 that receives liquid droplets when performing empty discharge for discharging liquid droplets that do not contribute to recording in order to discharge the thickened recording liquid. ing. Here, the cap 82a is a sucking and moisturizing cap (hereinafter referred to as "suction cap"), and the other caps 82b to 82d are moisturizing caps.

  Further, in the non-printing area on the other side of the carriage 23 in the scanning direction, there is an empty space for receiving a liquid droplet when performing an empty discharge for discharging a liquid droplet that does not contribute to recording in order to discharge the recording liquid thickened during recording or the like. A discharge receiver 88 is arranged, and the idle discharge receiver 88 is provided with openings 89 a to 89 d along the nozzle row direction of the recording head 31.

  In the ink jet recording apparatus configured as described above, the sheets 42 are separated and fed one by one from the sheet feeding tray 2, and the sheet 42 fed substantially vertically upward is guided by the guide 45, and the transport belt 51 and the counter roller 46, and the leading end is guided by the conveying guide 37 and pressed against the conveying belt 51 by the tip pressing roller 49, and the conveying direction is changed by approximately 90 °.

  At this time, a charging voltage pattern in which a positive voltage and a negative output are alternately repeated from the AC bias supply unit to the charging roller 56 by a control unit (not shown), that is, an alternating voltage is applied, and the conveying belt 51 alternates. That is, plus and minus are alternately charged in a band shape with a predetermined width in the sub-scanning direction which is the circumferential direction. 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 31 according to the image signal while moving the carriage 23, 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.

  During printing (recording) standby, the carriage 23 is moved to the maintenance / recovery mechanism 81 side, the recording head 31 is capped by the cap 82, and the nozzles are kept in a wet state to prevent ejection failure due to ink drying. . Further, the recording liquid is sucked from the nozzle by a suction pump (not shown) with the recording head 31 capped by the cap 82 (referred to as “nozzle suction” or “head suction”), and the thickened recording liquid and bubbles are discharged. Perform recovery action. In addition, an idle ejection operation for ejecting ink not related to recording is performed before the start of recording or during recording. Thereby, the stable ejection performance of the recording head 31 is maintained.

  Next, an example of a droplet discharge head constituting the recording head in this image forming apparatus will be described with reference to FIGS. 4 is a cross-sectional explanatory view along the longitudinal direction of the liquid chamber of the head, and FIG. 5 is a cross-sectional explanatory view of the head along the lateral direction of the liquid chamber (nozzle arrangement direction).

  The droplet discharge head includes a flow channel plate 101 formed by anisotropic etching of a single crystal silicon substrate, a vibration plate 102 formed by nickel electroforming, for example, bonded to the lower surface of the flow channel plate 101, and a flow plate. A nozzle plate 103 bonded to the upper surface of the path plate 101 is bonded and stacked, and a nozzle communication path 105, a liquid chamber 106, and a liquid chamber, which are channels through which the nozzles 104 that discharge liquid droplets (ink droplets) communicate with each other. An ink supply port 109 communicating with a common liquid chamber 108 for supplying ink to 106 is formed.

  In addition, two rows (only one row is shown in FIG. 6) of stacked piezoelectric elements as electromechanical conversion elements that are pressure generating means (actuator means) for pressurizing 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 for connecting to 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 composed of 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 surface of the nozzle plate 103 is the nozzle surface 31a described above.

  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 droplet discharge head configured as described above, for example, by lowering the voltage applied to the piezoelectric element 121 from the reference potential, the piezoelectric element 121 contracts, and the vibration plate 102 descends to expand the volume of the liquid chamber 106. As a result, 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 to change the volume of the liquid chamber 106. / By contracting the volume, the recording liquid in the liquid chamber 106 is pressurized, and droplets of the recording liquid are ejected (jetted) 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. The recording liquid is filled in 106. 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 maintenance / recovery mechanism 81 will be described with reference to FIG. This figure is a schematic explanatory view showing the maintenance and recovery mechanism partially expanded.
As described above, the maintenance / recovery mechanism 81 includes a cap holder 201A including a holding mechanism for holding the suction and moisturizing cap 82a and the moisturizing cap 82b, and a holding mechanism for holding the moisturizing cap 82c and the moisturizing cap 82d. , A blade holder 203 that holds a wiper blade 83 that is a blade made of an elastic body for cleaning (wiping) the nozzle surface 31a of the recording head 31, and a liquid that does not contribute to printing from the recording head 31. An empty discharge receiver 84 for performing an empty discharge operation (preliminary discharge operation) for discharging droplets is disposed.

  Here, a tubing pump (suction pump) 211 serving as a suction means is connected to the suction and moisture retention cap 82a closest to the print area via a flexible tube 210. Therefore, when performing the maintenance recovery operation of the recording head 31, the recording head 31 performing the recovery operation is selectively moved to a position where it can be capped by the cap 82a.

  A cam shaft 213 rotatably supported by the frame 212 is disposed below the cap holders 201A and 201B, and cap cams 214A and 214B for raising and lowering the cap holders 201A and 201B are disposed on the cam shaft 213. And a wiper cam 215 for moving the blade holder 203 up and down.

  In order to rotationally drive the tubing pump 211 and the cam shaft 213, the motor gear 222 provided on the motor shaft 221a is rotated with the pump gear 223 provided on the pump shaft 211a of the tubing pump 211, and the pump gear is further rotated. An intermediate gear 226 with a one-way clutch 227 is meshed with an intermediate gear 224 integral with the intermediate gear 225, and the intermediate gear 228 coaxial with the intermediate gear 226 is fixed to the camshaft 213 via the intermediate gear 229. The cam gear 230 is engaged.

  In the maintenance / recovery mechanism 81, when the motor 221 rotates in the forward direction, the motor gear 222, the intermediate gear 224, the pump gear 223, the intermediate gears 225 and 226 rotate, and the shaft 211a of the tubing pump 211 rotates to rotate the tubing pump 211. Is activated to suck the inside of the suction cap 82a (this operation is referred to as “in-cap suction” or “head suction”). Since the other gears 228 and thereafter are blocked by the one-way clutch 227, they do not rotate (activate).

  Further, since the one-way clutch 227 is connected by the reverse rotation of the motor 221, the rotation of the motor 221 is transferred to the cam gear 230 via the motor gear 222, the intermediate gear 224, the pump gear 223, the intermediate gears 225, 226, 228, and 229. As a result, the cam shaft 213 rotates. At this time, the tubing pump 211 has a structure that does not operate by reversing the pump shaft 211a. With the rotation of the cam shaft 213, the cap cams 214A and 214B and the wiper cam 215 are raised and lowered at predetermined timings, respectively.

  When cleaning the nozzle surface 31 a of the recording head 31, the wiper blade 83 is raised and the recording head 31 is moved relative to the wiper blade 83 to wipe the nozzle surface 31 a.

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 controls the entire image forming apparatus. The main control unit 301 includes a microcomputer that also serves as a control unit related to a recovery operation (maintenance operation) according to the present invention, and a microcomputer that controls printing. And a print control unit 302 configured as described above.

  Then, the main control unit 301 uses the main scanning motor 24 and the sub-scanning motor 58 as described above in order to form an image on the paper 42 based on the print processing information input from the communication circuit 300. Drive control is performed via the drive circuit 303 and the sub-scanning motor 304, and control such as sending print data to the print control unit 302 is performed.

  The main control unit 301 receives a detection signal from a carriage position detection circuit 305 that detects the position of the carriage 23, and the main control unit 301 controls the movement position and movement speed of the carriage 23 based on the detection signal. To do. The carriage position detection circuit 305 detects the position of the carriage 23 by, for example, reading and counting the number of slits of an encoder sheet arranged in the scanning direction of the carriage 23 with a photosensor mounted on the carriage 23. The main scanning motor drive circuit 303 rotates the main scanning motor 24 according to the carriage movement amount input from the main control unit 301 to move the carriage 23 to a predetermined position at a predetermined speed.

  Further, the main control unit 301 receives a detection signal from a conveyance amount detection circuit 306 that detects the movement amount of the conveyance belt 51, and the main control unit 301 moves the movement amount and movement speed of the conveyance belt 51 based on the detection signal. To control. The conveyance amount detection circuit 306 detects the conveyance amount by, for example, reading and counting the number of slits of the rotary encoder sheet attached to the rotation shaft of the conveyance roller 52 with a photo sensor. The sub-scanning motor driving circuit 304 rotates the sub-scanning motor 58 in accordance with the conveyance amount input from the main control unit 301 to rotate the conveyance roller 52 to move the conveyance belt 51 to a predetermined position at a predetermined speed. Move with.

  The main control unit 301 rotates the sheet feeding roller 43 once by giving a sheet feeding roller driving command to the sheet feeding roller driving circuit 307. The main control unit 301 rotationally drives the motor 221 of the maintenance / recovery mechanism 81 via the maintenance / recovery mechanism drive motor drive circuit 308, thereby raising and lowering the cap 82, raising and lowering the wiper blade 83, and the suction pump 211 as described above. Drive.

  The main control unit 301 drives and controls an ink supply motor for driving the pump of the supply unit via the ink supply motor drive circuit 311, and ink is supplied from the ink cartridge 10 loaded in the cartridge loading unit 4 to the sub tank 32. Replenish supply. At this time, the main control unit 301 controls replenishment supply based on a detection signal from the sub tank full tank sensor 312 that detects that the sub tank 32 is full.

  Further, the main control unit 301 takes in information stored in the non-volatile memory 316 provided in each ink cartridge 10 attached to the cartridge loading unit 4 through the cartridge communication circuit 314, performs necessary processing, and It is stored and held in a non-volatile memory (for example, EEPROM) 315 which is a main body storage means.

  Further, the main control unit 301 receives a detection signal from an environmental sensor 313 that detects environmental temperature and environmental humidity.

  The print control unit 302 generates pressure for discharging droplets of the recording head 31 based on the signal from the main control unit 301 and the carriage position and conveyance amount from the carriage position detection circuit 305 and the conveyance amount detection circuit 306. Data for driving the means is generated, and the above-mentioned image data is transferred to the head drive circuit 310 as serial data, and the transfer clock and latch signal necessary for transferring the image data and confirming the transfer, drop control, etc. In addition to outputting a signal (mask signal) etc. to the head drive circuit 310, it comprises a D / A converter, a voltage amplifier, a current amplifier, etc. for D / A converting the pattern data of the drive signal stored in the ROM. Drive waveform generation means and drive waveform selection means to be given to the head driver, one drive pulse (drive signal) or a plurality of drive parameters. Scan to generate a composed drive waveform (drive signal) to the head drive circuit 310.

  The head drive circuit 310 selectively selects a drive signal constituting a drive waveform supplied from the print control unit 302 based on image data corresponding to one row of the print head 31 that is input serially. The recording head 31 is driven by applying it to a driving element (for example, a piezoelectric element as described above) that generates energy for discharging the ink. At this time, by selecting a driving pulse constituting the driving waveform, for example, dots having different sizes such as large droplets (large dots), medium droplets (medium dots), and small droplets (small dots) can be distinguished. it can.

Next, an example of the print control unit 302 and the head drive circuit (head driver) 310 will be described with reference to FIG.
As described above, the print control unit 302 generates a drive waveform (common drive waveform) composed of a plurality of drive pulses (drive signals) within one printing cycle and outputs the drive waveform, and a print image. And a data transfer unit 402 for outputting a clock signal, a latch signal (LAT), and droplet control signals M0 to M3.

  The droplet control signals M0 to M3 are 2-bit signals for instructing opening / closing of an analog switch 415, which will be described later in the head driving circuit 310, for each droplet, and are selected according to the printing cycle of the common driving waveform. The state transitions to the H level (ON) in the power waveform, and the state transitions to the L level (OFF) when not selected.

  The head drive circuit 310 receives a transfer clock (shift clock) and serial image data (gradation data: 2 bits / CH) from the data transfer unit 402, and latches each register value of the shift register 411. The latch circuit 412 for latching, the decoder 413 for decoding the gradation data and the control signals M0 to M3 and outputting the result, and the logic level voltage signal of the decoder 413 to a level at which the analog switch 415 can operate. A level shifter 414 for conversion and an analog switch 415 that is turned on / off (opened / closed) by the output of the decoder 413 provided via the level shifter 414 are provided.

  The analog switch 415 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 401 is input thereto. Accordingly, when the analog switch 415 is turned on in accordance with the result of decoding the serially transferred image data (gradation data) and the control signals M0 to M3 by the decoder 413, a required drive signal constituting the common drive waveform can be obtained. Passing (selected) is applied to the piezoelectric element 121.

  When performing a maintenance operation for maintaining and recovering the performance of the recording head 31, the main control unit 301 controls the maintenance / recovery mechanism 81 and performs maintenance for the drive waveform generation unit 401 from the main control unit 301. Control is performed to generate a drive waveform (here, a sine wave drive waveform as will be described later), and image data for driving each pressure generating means of the recording head 31 is given to the data transfer unit 402 for maintenance. The piezoelectric element 121 of the recording head 31 is driven with the drive waveform for control to cause a pressure change in the liquid chamber 106.

Therefore, the recording head maintenance / recovery operation in this image forming apparatus will be described with reference to FIG.
First, the cleaning operation in the maintenance and recovery operation will be described with reference to FIG.
In the cleaning operation, as described above, by operating the suction pump 211 in a state where the nozzle surface 31a of the recording head 31 is capped by the suction cap 82a, the ink is sucked from the nozzle 104 of the recording head 31 and the nozzle surface 31a. The ink adhering to the recording head 31 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 31 is maintained and recovered.

  Here, as shown in FIG. 9A, while the nozzle surface 31a of the recording head 31 is capped by the suction cap 82a, the suction pump 211 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.

  As a result, as shown in FIG. 10, the pressure change in the liquid chamber 106 also occurs when foreign matter from the outside such as paper dust 500 is clogged in the hole of the nozzle 31n of the recording head 31 and discharge failure or discharge failure occurs. The paper dust 500 can be discharged to the cap 82a and removed.

  In this case, conditions for applying a drive waveform to the piezoelectric element 121 of the recording head 31, for example, an elapsed time (waiting time) n1 (ms) from the start of head suction, as shown in FIG. The number of droplets n2 (droplets)), the elapsed time n3 (ms) from the previous drive, and the total number of times of driving N (times) can be determined in advance or detected based on a detection signal from the environmental sensor 313. It can also be determined according to the environmental conditions or the number of printed sheets.

  In this way, by changing the pressure in the liquid chamber of the recording head in parallel with the head suction, the pressure that changes is more than that in the case of merely giving the pressure that does not change the volume in the liquid chamber (the pressure that does not change). Stable ejection performance can be given to 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 high image quality can be maintained.

Here, the maintenance drive waveform applied to the recording head 31 in parallel with the head suction will be described.
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 31. As a result, the pressure change in the liquid chamber 106 of the recording head 31 can be substantially maximized, and the pressure applied to the nozzle 104 is increased. As shown in FIG. It can be recovered at a higher recovery rate than when Tc is halved (Tc / 2) or twice the natural vibration period Tc (2Tc).

  In addition, unlike the drive waveform for printing normally used for printing, a drive waveform that is more likely to resonate with the natural vibration of the liquid chamber than the print drive waveform is used as the maintenance drive waveform. As a result, the pressure in the liquid chamber can be maximized, and recovery (removal of paper dust) can be performed at a high recovery rate, as shown in FIG.

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

  Further, by setting the driving frequency for maintenance to a driving frequency of 10 [kHz] or more, it becomes easy to resonate with the natural vibration period of the liquid chamber.

  Furthermore, as shown in FIG. 14, the timing for applying 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. ing.

  FIG. 14 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. A maintenance drive waveform is applied during the time (within the shaded area in the figure). In FIG. 14, the probability of occurrence of “◯, Δ, ×” indicates that “○” indicates no problem, “△” indicates that several nozzles are non-injected or bent, and “×” indicates that multiple nozzles are abnormal. Is shown.

  Thus, when the negative pressure in the cap is 50% or more of the maximum value, a maintenance operation can be performed without causing side effects by applying the maintenance drive waveform. That is, if the drive is performed in a state where the pressure (negative pressure) in the cap is low, bubbles are likely to be involved, 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. 15, in accordance with environmental conditions, 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. 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.

  Thus, even when the ink viscosity changes depending on the environment, the optimum recovery operation corresponding to the viscosity can be performed 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.

  In addition, it is preferable that the cleaning operation for applying the meniscus driving waveform is periodically performed according to, for example, the printing situation. When the number of printed sheets is large, foreign matters such as paper dust are likely to adhere. Therefore, the number of printed sheets is cumulatively counted, and when the number exceeds the number, the recovery operation is automatically performed. For example, as shown in FIG. 16, when the maintenance and recovery process is started, the cumulative number of printed sheets is read. If the cumulative number of printed sheets is less than a predetermined number, a normal cleaning operation without applying a maintenance drive waveform is performed. If the number is greater than or equal to the predetermined number of sheets, a cleaning operation for applying a maintenance drive waveform (with idle ejection) may be performed to reset the cumulative print number counter used in this process.

  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 perspective view illustrating an example of an image forming apparatus according to the present invention as viewed from the front side. 2 is a configuration diagram illustrating an outline of a mechanism unit of the image forming apparatus. FIG. It is principal part plane explanatory drawing of the mechanism part. FIG. 4 is a cross-sectional explanatory view along the longitudinal direction of the liquid chamber showing an example of a droplet discharge head constituting the recording head of the image forming apparatus. It is sectional explanatory drawing along the liquid chamber transversal direction of the head. FIG. 3 is a development schematic explanatory view of a maintenance / recovery mechanism of the image forming apparatus. FIG. 2 is a block explanatory diagram illustrating an overview of a control unit of the image forming apparatus. It is a block diagram which shows an example of the printing control part of the control part. It is explanatory drawing with which description of the maintenance recovery operation | movement which concerns on this invention is provided. It is explanatory drawing with which it uses for description of an abnormal nozzle. It is explanatory drawing which shows an example of the drive waveform for a maintenance. It is explanatory drawing explaining an example of the relationship between the period of the drive waveform for a maintenance with respect to the natural vibration period Tc of a liquid chamber, and a recovery rate. It is explanatory drawing explaining the difference in the recovery rate when a maintenance drive waveform and a printing drive waveform are the same and different. 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 a flowchart with which it uses for description of an example of the maintenance recovery process which performs operation | movement which uses the drive waveform for maintenance according to the number of printed sheets, and operation | use which is not used.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Ink cartridge 23 ... Carriage 31 ... Recording head 32 ... Sub tank 51 ... Conveyance belt 81 ... Maintenance recovery mechanism 82a ... Suction cap 82b-82d ... Moisturizing cap 301 ... Main control part 313 ... Environmental sensor 401 ... Drive waveform generation part 402: Data transfer unit

Claims (9)

  A recording head having a nozzle for discharging droplets of the recording liquid, a liquid chamber in which the nozzle communicates, a pressure generating means for generating pressure to pressurize the recording liquid in the liquid chamber, and a nozzle surface of the recording head are capped with a cap member. In the image forming apparatus that includes a maintenance / recovery mechanism for sucking the recording liquid from the nozzle and forms an image on a recording medium by ejecting liquid droplets from the nozzle of the recording head, the cap member is capped. An image forming apparatus comprising: means for performing a maintenance operation for driving a pressure generating means of the recording head to cause a pressure change in the liquid chamber while the recording liquid is sucked from the nozzle.   The image forming apparatus according to claim 1, wherein in the maintenance operation, a driving waveform having a period substantially the same as a natural vibration period in the liquid chamber of the recording head is applied to the pressure generating unit.   3. The image forming apparatus according to claim 1, wherein the time during which the drive waveform is applied is a time during which the pressure in the cap member is 50% or more of the maximum pressure. 4.   4. The image forming apparatus according to claim 1, wherein a peak value of the drive waveform varies depending on environmental conditions.   5. The image forming apparatus according to claim 1, wherein a drive waveform used in the maintenance operation is different from a drive waveform used in image formation.   6. The image forming apparatus according to claim 1, wherein the drive waveform is a sine wave. 7. The image forming apparatus according to claim 1, wherein a driving frequency of the driving waveform is 10 kHz or more.   8. The image forming apparatus according to claim 1, wherein the maintenance operation is performed according to the number of printed sheets. In the recovery method of a recording head, the nozzle surface of the recording head that discharges a recording liquid droplet is capped with a cap member, and the recording liquid is sucked from the nozzle to recover the performance of the nozzle of the head. A method for recovering a recording head, wherein the recording head is driven to cause a pressure change in the liquid chamber while the recording liquid is sucked from the nozzle by capping.

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