JP5320700B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus provided with a recording head for discharging droplets.

  As an image forming apparatus such as a printer, a facsimile machine, a copying machine, and a multifunction machine of these, for example, a recording head composed of a liquid discharge head that discharges liquid droplets of a recording liquid (liquid) is used. However, the material is not limited, and a recording medium, a recording medium, a transfer material, a recording paper, and the like are also used synonymously.) While conveying a recording liquid (hereinafter also referred to as ink). Is attached to a sheet to form an image (recording, printing, printing, and printing are also used synonymously).

  In the present application, the “image forming apparatus” means an apparatus that forms an image by ejecting ink droplets onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, Further, “image formation” not only means that an image having a meaning such as a character or a figure is imparted to the medium, but also that an image having no meaning such as a pattern is imparted to the medium. Further, “ink” is not limited to ink in a narrow sense, and is not particularly limited as long as it is a liquid capable of performing image formation in the above sense.

In such an image forming apparatus, in order to prevent the ink in the nozzles of the recording head from thickening and causing clogging, for example, as described in Patent Document 1, printing is performed within one printing cycle. In addition to the drive pulse, a non-ejection drive pulse that slightly vibrates the meniscus to the extent that droplets are not ejected is applied.
JP 2005-041039 A

Also, as described in Patent Document 2, there is a technique in which a non-ejection drive pulse (fine drive pulse) is applied based on the temperature and humidity near the nozzle.
JP 2006-248130 A

In addition, there are the following documents regarding non-ejection driving of the nozzle meniscus.
Japanese Patent Laying-Open No. 2005-212411 Japanese Patent No. 3741186

  By the way, a water-repellent layer is formed on the nozzle surface of the recording head. However, when ink adheres to the nozzle surface and dries, the meniscus holding power on the dried ink is weaker than that on the water-repellent layer, resulting in poor ejection. It has been found that there is a problem that (bending in the discharge direction) occurs.

  Although the above-described conventional fine driving (non-ejection driving) has a degree of difference (difference in vibration magnitude), the meniscus is vibrated (finely driven so as not to overflow the nozzle meniscus from the periphery of the nozzle). ). This is because fine driving is intended to suppress the viscosity increase of the ink in the nozzle, and it is sufficient to vibrate the meniscus.

  The present invention has been made in view of the above problems, and an object of the present invention is to prevent dry ink from being generated on the nozzle surface of a recording head and to prevent ejection failure due to dry ink.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A recording head having nozzles for discharging droplets;
Drive waveform generating means for generating a drive waveform including a drive signal for driving the recording head;
Means for applying the driving signal generated by the driving waveform generating means to the pressure generating means of the recording head,
The drive waveform generating means includes
A first driving waveform including a driving signal for performing printing by discharging the droplet;
A drive signal for performing printing by discharging the droplets constituting the first drive waveform, and a drive signal for causing the liquid in the nozzle to overflow to the periphery of the nozzle opening in a state where the droplet does not become a droplet, and Generating a second drive waveform having one drive cycle longer than the first drive waveform;
The second drive waveform is, only when a predetermined condition a predetermined and configured to be Repetition rate selected.

By the present invention lever, to reduce the drying liquid is caused that the nozzle surface of the record head may be so poor no ejection by generation of drying the liquid.

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 image forming apparatus, and a carriage 33 is slidable in the main scanning direction by main and slave guide rods 31 and 32 which are guide members horizontally mounted on the left and right side plates 21A and 21B of the apparatus main body 1. It is held and moved and scanned in the direction indicated by the arrow (carriage main scanning direction) in FIG.

  The carriage 33 is provided with recording heads 34a and 34b (which are liquid ejection heads according to the present invention for ejecting ink droplets of yellow (Y), cyan (C), magenta (M), and black (K). When not distinguished, it is referred to as “recording head 34”). A nozzle row composed of a plurality of nozzles is arranged in the sub-scanning direction orthogonal to the main scanning direction, and is mounted with the ink droplet ejection direction facing 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.

  The carriage 33 is equipped with sub tanks 35a and 35b (referred to as “sub tanks 35” when not distinguished) for supplying ink of each color corresponding to the nozzle rows of the recording head 34. The sub tank 35 receives the recording liquid of each color from the recording liquid cartridges 10 y, 10 m, 10 c, and 10 k detachably attached to the cartridge loading unit 4 via the supply tube 36 of each color by the supply pump unit 5. Replenished.

  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, as shown in FIG. 2, a maintenance / recovery mechanism 81 for maintaining and recovering the state of the nozzles 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 liquid, 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, A wiper cleaner portion 85 that is integrally formed with the idle discharge receiver 84 and is a cleaning member for removing ink adhering to the wiper blade 83, and a wiper cleaner 86 that presses the wiper blade 83 toward the wiper cleaner 85 when the wiper blade 83 is cleaned. And a carriage lock 87 for locking the carriage 22.

  In addition, as shown in FIG. 2, in the non-printing area on the other side in the scanning direction of the carriage 33, idle discharge is performed to discharge liquid droplets that do not contribute to recording in order to discharge the recording liquid thickened during recording or the like. An empty discharge receiver 88 for receiving the liquid droplets at the time is disposed, and the empty discharge receiver 88 is provided with 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 idle ejection for ejecting droplets that do not contribute to image formation, image formation by stable droplet ejection can be performed.

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

  The liquid discharge head includes, for example, a flow path plate 101 formed by etching a SUS substrate or 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, and a flow path. The nozzle plate 103 bonded to the upper surface of the plate 101 is bonded and stacked, and the nozzle communication path 105, the liquid chamber 106, and the liquid chamber 106, which are channels through which the nozzle 104 that discharges droplets (ink droplets) communicates. An ink supply port 109 communicating with a common liquid chamber 108 for supplying ink to the liquid 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 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 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 becomes the nozzle surface 31a.

  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 configured as described above, for example, by lowering the voltage applied to the piezoelectric element 121 from the reference potential Ve, the piezoelectric element 121 contracts, and the diaphragm 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 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 includes a main control unit 301 configured by a microcomputer that controls the entire image forming apparatus and a print control unit 302 configured by a microcomputer that controls printing.

  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 as described above. Drive it.

  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 nonvolatile memory 316 which is a storage unit provided in each ink cartridge 10 mounted on the cartridge loading unit 4 through the cartridge communication circuit 314, and performs a necessary process. And stored in a non-volatile memory (for example, EEPROM) 315 which is a main body storage means.

  The main control unit 301 receives a detection signal from an environmental sensor 313 that detects environmental temperature and environmental humidity (environmental conditions).

  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 supplied to the head driver. One drive pulse (drive signal) or a plurality of drive parameters Scan to generate a plurality including driving waveform drive signal group consisting of (a drive signal) output 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 (driving signal) of a driving signal group constituting a driving waveform, it is possible to eject droplets having different sizes and to sort dots having different sizes.

Next, an example of the print control unit 302 and the head drive circuit (head driver) 310 will be described with reference to FIG.
The print control unit 302 generates a drive waveform (common drive waveform) and outputs a drive waveform generation unit 401 that is a drive signal generation unit, and 2-bit image data (tone signals 0 and 1) corresponding to the print image. And a data transfer unit 402 that also serves as a selection unit that outputs a clock signal, a latch signal (LAT), and droplet control signals MN0a to MN3a and MN0b to MN3b.

  Here, the drive waveform generation unit 401 generates and outputs a drive waveform (common drive waveform) composed of one or a plurality of drive signals (drive pulses) within one drive cycle (one print cycle). Further, the data transfer unit 402 outputs droplet control signals MN0 to MN for selecting a drive signal included in the drive waveform output from the drive waveform generation unit 401 for each drive cycle. The droplet control signals MN0 to MN3 are 2-bit signals that instruct the opening and closing of the analog switch 415 that is the switch means of the head driving circuit 310 for each droplet, and the state transitions to the L level with the driving signal to be selected. When not selected, the state transitions to the H level.

  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 by the decoder, the decoder 413 for decoding the image data and the droplet control signals MN0 to MN3 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 droplet control signals MN0 to MN3 by the decoder 413, the required drive signal included in the common drive waveform Is passed (selected) and applied to the piezoelectric element 121.

Therefore, a first embodiment of the present invention will be described with reference to FIG. FIG. 7 is an explanatory diagram showing an example of a drive waveform output from the drive waveform generator 401.
As shown in FIG. 7A, the drive waveform PV generated and output (generated) from the drive waveform generation unit 401 includes six drive signals (drive pulses) P1 output in time series within one drive cycle. ~ P6.

  The drive signal P1 is a fine drive signal that vibrates the ink in the nozzle 104 in a state where it does not become a droplet, a waveform element that falls from the reference potential Ve, a waveform element that is held at the potential after the fall, and a reference potential Ve after the hold. Consists of waveform elements that rise up as they are. The drive signals P2 and P3 are ejection drive signals for ejecting droplets. The waveform element falls from the reference potential Ve, the waveform element held at the potential after the fall, and the waveform element that rises stepwise to the reference potential Ve after the hold. Consists of. The drive signal P4 is an ejection drive signal for ejecting droplets, and includes a waveform element that falls from the reference potential Ve, a waveform element that is held at the potential after the fall, and a waveform element that rises as it is to the reference potential Ve after being held. . The drive signal P5 is an ejection drive signal for ejecting droplets, and includes a waveform element that falls from the reference potential Ve, a waveform element that is held at the potential after the fall, and a waveform that rises to a required potential after the held reference potential Ve. Element, a waveform element that rises after holding, and a waveform element that falls to the reference potential after holding.

  The drive signal P6 is a drive signal (hereinafter referred to as “overflow drive”) that causes the ink in the nozzle 104 to overflow to the periphery of the nozzle opening (nozzle opening means an opening portion with respect to the nozzle surface 31a) in a state where it does not become a droplet. 7 (c) and FIG. 8 (a), the waveform element that falls from the reference potential Ve to the potential V6 with the falling time constant tr6 and held at the potential after the fall, as shown in FIGS. And a waveform element that rises as it is with a rise time constant tf6 to the reference potential Ve after holding.

  The drive signals P1 to P6 of the drive waveform PV are selected by the droplet control signal MN as described above. For example, when the fine drive signal P1 is selected, the drive waveform shown in FIG. 7B is applied to the pressure generating means of the recording head, and when the overflow drive signal P6 is selected, the drive waveform shown in FIG. The pressure is applied to the pressure generating means (in this example, the piezoelectric element 121) of the recording head 34.

Here, the difference between the overflow drive signal P6 and the normal fine drive signal P1 conventionally used will be described with reference to FIG.
As shown by a broken line in FIG. 8A, the fine drive signal P1 falls from the reference potential Ve to the potential V1 with the time constant tr1, and rises to the reference potential Ve with the time constant tf1 after the hold (FIG. 7B). (See) Waveform. When this fine drive signal P1 is applied, as shown by a broken line in FIG. 8B, the meniscus position is drawn into the nozzle 104 by the falling waveform element of the fine drive signal P1, and the liquid chamber 106 is drawn by the rising waveform element. Since the pressure is applied, it advances beyond the initial position, but since the drive voltage is small (the fall amount is small), the meniscus 100a of the ink 100 in the nozzle 104 is, for example, as shown in FIG. The nozzle 104 only protrudes from the nozzle opening (nozzle surface 31a) without overflowing the periphery 104a of the nozzle opening. The meniscus fluctuation speed changes as shown by the broken line in FIG.

  Therefore, when only the fine driving signal P1 is applied, for example, when an adhering material 500 such as ink is present in the portion 104a around the nozzle opening as shown in FIG. Thus, even if the meniscus 100a returns to the inside of the nozzle 104, the deposit 500 is left as it is in the periphery 104a of the nozzle opening, and the deposit 500 is dried.

  In contrast, the overflow drive signal P6 has a drive voltage falling from the reference potential Ve to the potential V6 with a time constant tr6 as shown by a solid line in FIG. 8A and rises with a time constant tf6 after the hold (FIG. 7 ( c) Reference) Waveform. When this overflow drive signal P6 is applied, the meniscus position is drawn into the nozzle 104 by the falling waveform element of the overflow drive signal P6 as shown by the solid line in FIG. Since it is pressurized, it advances beyond the initial position. At this time, since the drive voltage is larger than the fine drive signal P1 (the falling amount is large), for example, as shown in FIG. 10A, the meniscus 100a of the ink 100 in the nozzle 104 overflows around the periphery 104a of the nozzle opening. It becomes a state.

  Then, the next print drive signal (for example, when the nozzle is ejected in the next drive cycle) or the next overflow drive signal P6 (for example, the nozzle is not ejected in the next drive cycle) is set. At the time of lowering, the meniscus 100a returns to the state shown in FIG. 10B, and at this time, ink (attachment) adhering to the periphery 104a of the nozzle opening is drawn into the nozzle 104. The overflow drive signal P6 has a large drive voltage, but since the voltage is gradually changed by increasing the time constants tr6 and tf6, no droplet is ejected. Further, the meniscus fluctuation speed changes as shown by a solid line in FIG. 8C and is almost the same as the fine drive signal P1.

  Therefore, when the overflow driving signal P6 is applied, if the deposit 500 such as ink is present around the nozzle opening 104a as shown in FIG. 10A, the overflow ink 100 is combined with the deposit 500. Then, as described above, when returning to the nozzle 104 by the next print drive signal or overflow drive signal, the deposit 500 is also taken into (drawn in) the ink 100 and returned to the nozzle 104 as shown in FIG. As a result, the deposit 500 is not dried.

  As a result, it is possible to prevent dry ink from being generated on the nozzle surface of the recording head, and to prevent ejection failure due to dry ink.

  Specifically, as shown in FIG. 11A, if there is no ink adhering around the nozzle opening 104a (especially the nozzle edge), the above-mentioned fine drive signal P1 is given to the inside of the nozzle 104. By causing the ink 100 to vibrate, the viscosity increase of the ink in the nozzle 104 can be suppressed. However, when the water repellency of the nozzle surface 31a is lowered, as described above, the deposit 500 such as ink is generated around the nozzle opening 104a, and the nozzle 104 is not used for printing for a long time. In the meniscus vibration by the fine drive signal P1 described above, the ink 100 protruding from the nozzle 104 does not merge with the deposit 500, and the deposit 500 is thickened and dried as shown in FIG. A solid or film (dry film) 501 is obtained.

  When the dry film 501 in which such ink is dried does not exist around the nozzle opening 104a, the meniscus 400 is normally formed at the nozzle opening as shown in FIG. It is discharged as a droplet. On the other hand, when the solid ink or the dried film 501 is present around the nozzle opening 104a, particularly at the nozzle edge, the meniscus comes into contact with the dried film 501 as shown in FIG. When it is performed, the droplets cannot be normally cut between the dry film 501 and problems such as jet bending and nozzle down such as the droplets being ejected in the direction of arrow B occur.

  Therefore, as described above, the overflow drive signal P6 is given to overflow the ink 100 to the periphery 104a of the nozzle opening, and the deposit 500 is combined with the ink 500 and drawn into the nozzle 104, so that the deposit 500 is solidified or Film formation is prevented, a normal meniscus can be maintained, and no injection bending or nozzle down occurs.

Next, another example of the drive waveform output from the drive waveform generator 401 will be described with reference to FIG.
As shown in FIG. 13A, the drive waveform PV is composed of six drive signals (drive pulses) P11 to P16 output in time series within one drive cycle, and the drive signals P11, P12, P14 and P15 are drive signals for ejecting droplets, drive signal P13 is a fine drive signal, and drive signal P16 is an overflow drive signal. As described above, when the fine drive signal P13 is selected by the droplet control signal, the signal shown in FIG. 5B is output, and when the overflow drive signal P16 is selected, the signal shown in FIG. Thus, the fine drive signal P13 can be inserted in the middle of the drive waveform.

Next, a second embodiment of the present invention will be described with reference to FIGS. 14 is a functional block explanatory diagram of the main embodiment, FIG. 15 is an explanatory diagram showing an example of the drive waveform of the same embodiment, and FIG. 16 is a flowchart for explaining the operation of the selection unit.
In this embodiment, the data storage unit 601 that stores the data of the first drive waveform PV1, the data storage unit 602 that stores the data of the second drive waveform PV2, and the drive of any of these data storage units 601 and 602. A selection unit 603 that reads data of the waveforms PV1 and PV2 and supplies the data to the D / A conversion unit 604, and an amplification unit 605 that amplifies and outputs the drive waveform converted by the D / A conversion unit 604 are provided.

  Here, as shown in FIG. 15A, the first drive waveform PV1 is a drive waveform without the overflow drive signal P6 of the drive waveform PV of the first embodiment described above (the fine drive signal P1 is included). .) Further, as shown in FIG. 15B, the second drive waveform PV2 is the same drive waveform as the drive waveform PV of the first embodiment described above, and includes the overflow drive signal P6 together with the fine drive signal P1. It is a waveform.

  The selection unit 603 also refers to the flowchart shown in FIG. 16, and based on the detection result of the environment sensor 313, when the in-machine environment (in-device environment) condition is a temperature of 25 ° C. or more and a humidity of 30% or less, The second drive waveform PV2 is selected, and the first drive waveform PV1 is selected under other environmental conditions (specifically, the drive waveform data is given to the D / A converter 604).

  In other words, as described above, even if the deposit 500 adheres to the periphery 104a of the nozzle opening, there is a possibility that jet bending or nozzle down may occur under environmental conditions where the deposit 500 does not dry and become a solid or film. To reduce. Therefore, it is sufficient to apply the overflow drive signal P6 only under a predetermined environmental condition, that is, an environmental condition in which ink adheres around the nozzle opening of the recording head and dries.

  In this case, it is possible to always generate only the drive waveform including the overflow drive signal P6 and select the overflow drive signal P6 by the droplet control signal as described above under predetermined environmental conditions.

  However, the drive waveform in which the overflow drive signal P6 is inserted as in the second drive waveform PV2 is one drive cycle (all necessary drive signals are output) compared to the first drive waveform PV not including the overflow drive signal P6. If the printing is always performed using the second drive waveform PV2, the printing speed is reduced as a result.

  Therefore, as in this embodiment, the overflow drive signal P6 is included only when the environmental conditions are predetermined, that is, under the environmental conditions in which ink adheres to the periphery 104a of the nozzle openings of the recording head 34 and dries. Two driving waveforms are generated (selected) (the printing speed and the carriage speed are reduced by the amount of the waveform extension), and the overflow driving signal P6 is selected by the droplet control signal. As a result, it is possible to reduce the possibility of jet bending and nozzle down without causing unnecessary reduction in printing speed.

  In the above embodiments, 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. As described above, the “ink” in the present application includes a fixing processing liquid for modifying the surface properties on the medium.

1 is a configuration diagram illustrating an example of an image forming apparatus according to the present invention. It is principal part plane explanatory drawing of the mechanism part. FIG. 3 is an explanatory cross-sectional view along the longitudinal direction of the liquid chamber showing an example of a liquid discharge head that constitutes the recording head of the image forming apparatus. It is sectional explanatory drawing along the liquid chamber transversal direction of the head. 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 which shows an example of the drive waveform with which it uses for description of 1st Embodiment of this invention. It is explanatory drawing with which it uses for description of the difference of the fine drive signal P1 and the overflow drive signal P6 of the same drive waveform. It is explanatory drawing with which it uses for description of the state of a meniscus when a fine drive signal is applied similarly. It is explanatory drawing with which it uses for description of the state of a meniscus when an overflow drive signal is applied similarly. It is explanatory drawing with which it uses for description of generation | occurrence | production of the dry film | membrane around nozzle opening similarly. It is explanatory drawing similarly used for description of the presence or absence of a dry film, and a droplet discharge state. It is explanatory drawing which shows the other example of the drive waveform with which it uses for description of the embodiment. It is a functional block explanatory drawing of the part which concerns on the drive waveform generation and selection with which it uses for description of 2nd Embodiment of this invention. It is explanatory drawing explaining two types of drive waveforms similarly. It is a flowchart with which it uses for description of the process of a selection part similarly.

Explanation of symbols

33 ... Carriage 34 ... Recording head (liquid ejection head)
DESCRIPTION OF SYMBOLS 100 ... Ink 100a ... Meniscus 104 ... Nozzle 104a ... Around nozzle opening 301 ... Main control part 302 ... Print control part 310 ... Head drive circuit 401 ... Drive waveform generation part 402 ... Data transfer part

Claims (3)

A recording head having nozzles for discharging droplets;
Drive waveform generating means for generating a drive waveform including a drive signal for driving the recording head;
Means for applying the driving signal generated by the driving waveform generating means to the pressure generating means of the recording head,
The drive waveform generating means includes
A first driving waveform including a driving signal for performing printing by discharging the droplet;
A drive signal for performing printing by discharging the droplets constituting the first drive waveform, and a drive signal for causing the liquid in the nozzle to overflow to the periphery of the nozzle opening in a state where the droplet does not become a droplet, and Generating a second drive waveform having one drive cycle longer than the first drive waveform;
Wherein the second drive waveform, the image forming apparatus characterized by only being Repetition rate selected to when a predetermined condition set in advance.   The image forming apparatus according to claim 1, wherein the first drive waveform includes a fine drive signal that vibrates the liquid in the nozzle in a state where the liquid droplet does not become the droplet.   3. The image forming apparatus according to claim 1, wherein the second drive waveform includes a fine drive signal that vibrates the liquid in the nozzle in a state where the liquid droplet does not become the droplet.

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