JP4355528B2 - Image forming apparatus - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus using a droplet discharge head.
[0002]
[Prior art]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-81012
In an ink jet recording apparatus used as an image forming apparatus such as a printer, a facsimile, a copying apparatus, or a plotter, an ink jet head that ejects ink droplets is mounted as a liquid droplet ejecting head. In this ink jet head, a piezoelectric element is used as a pressure generating means for pressurizing ink in the ink flow path (pressure generating chamber), and the diaphragm that forms the wall surface of the ink flow path is deformed to change the volume of the ink flow path. A so-called piezo-type that discharges ink droplets, or a so-called thermal-type that discharges ink droplets with pressure generated by heating the ink in the ink flow path using a heating resistor to generate bubbles, The diaphragm and the electrode forming the wall surface of the ink flow path are arranged opposite to each other, and the diaphragm is deformed by an electrostatic force generated between the vibration plate and the electrode, thereby changing the volume of the ink flow path to change the ink droplet. An electrostatic type that discharges water is known.
[0004]
As a driving method of such an ink jet head, there are a driving method in which a vibration plate is pushed into the pressure generating chamber side and the volume in the pressure generating chamber is reduced to eject ink droplets, and a vibration plate is driven in the ink chamber. There are some which are driven by a striking method in which ink droplets are ejected by returning the displacement of the vibration plate to the original volume from the state in which the inner volume in the ink chamber is expanded by being deformed by the force of the outer side of the ink chamber. .
[0005]
In addition, in order to perform gradation printing, the first drive pulse for ejecting the first ink droplet within one printing cycle and the first ink droplet are large as disclosed in Japanese Patent Application Laid-Open No. 2004-228561. And a second drive pulse for discharging different ink droplets, and a combination of the first and second drive pulses enables selection of four or more gradations.
[0006]
[Problems to be solved by the invention]
However, as disclosed in [Patent Document 1], when droplets are ejected by applying a plurality of drive pulses within one printing cycle, the nozzle surface is soiled by droplet ejection, and the droplets are ejected in the soiled state. Since the ejection is attempted, there is a problem that an image quality abnormality such as a jet bending or a nozzle down is likely to be caused.
[0007]
The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus in which high quality image quality is obtained by preventing nozzle bending even when continuous discharge is performed, preventing jet bending, nozzle down, and the like. To do.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problems, an image forming apparatus according to the present invention includes a plurality of ejection driving pulses that are output in a time series in order to eject droplets and a meniscus that does not eject droplets within one printing cycle. to both the waveform element of the non-ejection drive pulses to provide a slight vibration, a first signal for expanding the pressure generating chamber, after the first signal, a second signal for holding the expanded state of the pressure generating chamber A part of the timing of ejecting the droplets of the ejection drive pulse generated as a drive pulse including the third signal for contracting the pressure generating chamber after the second signal and applied to the nozzle for ejecting the droplets When it was configured to the application timing of the non-ejection driving pulse applied to the non-discharge nozzle which does not eject droplets is duplicated.
[0009]
Here, a first gradation value that does not eject a droplet by selecting a non-ejection driving pulse, and a second gradation value that causes one of a plurality of ejection driving pulses to be ejected and a droplet are ejected. In this case, a droplet is ejected by selecting an ejection drive pulse other than the ejection drive pulse selected at the second gradation value or two or more ejection drive pulses including the ejection drive pulse selected at the second gradation value. And a fourth gradation value for ejecting droplets by selecting three or more ejection drive pulses including the ejection drive pulse selected by the third gradation value can be selected. preferable.
[0010]
Further, it is preferable that the time interval between time series output by the plurality of ejection driving the droplet ejection timing by Dopa pulse is an integer multiple of the natural vibration period Tc of the pressure generating chamber.
[0011]
Further, it is preferable that the droplets ejected by the plurality of ejection drive pulses output in time series have a faster droplet velocity as the droplet ejected by the temporally slower ejection drive pulse.
[0012]
In addition, at least one of the plurality of ejection drive pulses contracts the pressure generation chamber to eject the droplet, and the pressure after a lapse of Tc / 4 to 3Tc / 4 hours when Tc is the natural vibration period of the pressure generation chamber. It is preferable to include a signal that contracts the generation chamber and suppresses residual vibration of the meniscus after droplet discharge.
[0013]
Alternatively, at least one of the plurality of ejection driving pulses contracts the pressure generation chamber to eject a droplet, and after the elapse of Tc / 4 to 3Tc / 4 hours, where Tc is the natural vibration period of the pressure generation chamber. It is preferable that the pressure generation chamber be contracted and include a signal for expanding the pressure generation chamber after a lapse of Tc / 2 hours to suppress the residual vibration of the meniscus after the droplet is discharged.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic perspective view of a mechanism portion of an ink jet recording apparatus as an image forming apparatus according to the present invention, and FIG. 2 is a side view of the mechanism portion.
[0015]
The ink jet recording apparatus includes a carriage that can move in the main scanning direction inside the recording apparatus main body 1, a recording head that includes an ink jet head mounted on the carriage, an ink cartridge that supplies ink to the recording head, and the like. The mechanism unit 2 and the like are accommodated, the paper 3 fed from the paper feed cassette 4 or the manual feed tray 5 is taken in, a required image is recorded by the printing mechanism unit 2, and then the paper discharge tray 6 mounted on the rear side is loaded. Eject paper.
[0016]
The printing mechanism unit 2 holds the carriage 13 slidably in the main scanning direction (vertical direction in FIG. 2) with a main guide rod 11 and a sub guide rod 12 which are guide members horizontally mounted on left and right side plates (not shown). The carriage 13 has a head 14 composed of an inkjet head for discharging ink droplets of yellow (Y), cyan (C), magenta (M), and black (Bk) with the ink droplet discharge direction directed downward. Each ink tank (ink cartridge) 15 for supplying ink of each color to the head 14 is replaceably mounted on the carriage 13.
[0017]
The ink cartridge 15 has an air port that communicates with the atmosphere upward, a supply port that supplies ink to the inkjet head 14 below, and a porous body filled with ink inside. The ink supplied to the inkjet head 14 by the force is maintained at a slight negative pressure. Ink is supplied from the ink cartridge 15 into the head 14.
[0018]
Here, the carriage 13 is slidably fitted to the main guide rod 11 on the rear side (downstream side in the paper conveyance direction), and is slidably mounted on the secondary guide rod 12 on the front side (upstream side in the paper conveyance direction). is doing. In order to move and scan the carriage 13 in the main scanning direction, a timing belt 20 is stretched between a driving pulley 18 and a driven pulley 19 that are rotationally driven by a main scanning motor 17. The carriage 13 is reciprocally driven by forward and reverse rotation of the main scanning motor 17.
[0019]
Further, although the heads 14 of the respective colors are used here as the recording heads, a single head having nozzles that eject ink droplets of the respective colors may be used. Further, as will be described later, a vibration plate that forms at least a part of the wall surface of the ink flow path and a piezo-type inkjet head that deforms the vibration plate with a piezoelectric element are used as the head 14.
[0020]
On the other hand, in order to convey the paper 3 set in the paper feed cassette 4 to the lower side of the head 14, the paper feed roller 21 and the friction pad 22 for separating and feeding the paper 3 from the paper feed cassette 4 and the paper 3 are guided. A guide member 23, a transport roller 24 that reverses and transports the fed paper 3, a transport roller 25 that is pressed against the peripheral surface of the transport roller 24, and a tip that defines the feed angle of the paper 3 from the transport roller 24 A roller 26 is provided. The transport roller 24 is rotationally driven by a sub-scanning motor 27 through a gear train.
[0021]
A printing receiving member 29 is provided as a paper guide member for guiding the paper 3 fed from the transport roller 24 below the recording head 14 in accordance with the range of movement of the carriage 13 in the main scanning direction. A conveyance roller 31 and a spur 32 that are rotationally driven to send the paper 3 in the paper discharge direction are provided on the downstream side of the printing receiving member 29 in the paper conveyance direction, and the paper 3 is further delivered to the paper discharge tray 6. A roller 33 and a spur 34, and guide members 35 and 36 that form a paper discharge path are disposed.
[0022]
At the time of recording, the recording head 14 is driven according to the image signal while moving the carriage 13 to eject ink onto the stopped paper 3 to record one line, and after the paper 3 is conveyed by a predetermined amount, Record the line. Upon receiving a recording end signal or a signal that the trailing edge of the sheet 3 has reached the recording area, the recording operation is terminated and the sheet 3 is discharged.
[0023]
A recovery device 37 for recovering defective ejection of the head 14 is disposed at a position outside the recording area on the right end side in the movement direction of the carriage 13. The recovery device 37 includes a cap unit, a suction unit, and a cleaning unit. While waiting for printing, the carriage 13 is moved to the recovery device 37 side, and the head 14 is capped by the capping means, and the ejection port portion (nozzle hole) is kept in a wet state to prevent ejection failure due to ink drying. Further, by ejecting (purging) ink not related to recording during recording or the like, the ink viscosity of all the ejection ports is made constant and stable ejection performance is maintained.
[0024]
When a discharge failure occurs, the discharge port (nozzle) of the head 14 is sealed with a capping unit, and bubbles and the like are sucked out from the discharge port with a suction unit through the tube. Is removed by the cleaning means to recover the ejection failure. Further, the sucked ink is discharged to a waste ink reservoir (not shown) installed at the lower part of the main body and absorbed and held by an ink absorber inside the waste ink reservoir.
[0025]
Next, an ink jet head constituting the recording head 14 of the ink jet recording apparatus will be described with reference to FIGS. 3 is an explanatory sectional view along the longitudinal direction of the liquid chamber of the head, FIG. 4 is an explanatory sectional view along the lateral direction of the liquid chamber of the head, and FIG. 5 is an explanatory plan view of the main part of the head.
[0026]
The inkjet head includes a flow path plate 41 formed of a single crystal silicon substrate, a vibration plate 42 bonded to the lower surface of the flow path plate 41, and a nozzle plate 43 bonded to the upper surface of the flow path plate 41. As a result, the nozzle 45 that discharges ink droplets as droplets is an ink in a pressure chamber 46 that is an ink flow path that communicates via a nozzle communication path 45a, and a common liquid chamber 48 that supplies ink to the pressure chamber 46. An ink supply path 47 serving as a fluid resistance portion communicating with the supply port 49 is formed.
[0027]
An electromechanical conversion which is a pressure generating means (actuator means) for pressurizing the ink in the pressurizing chamber 46 corresponding to each pressurizing chamber 46 on the outer surface side (the surface opposite to the liquid chamber) of the vibration plate 42. A laminated piezoelectric element 52 as an element is bonded, and the piezoelectric element 52 is bonded to a base substrate 53. Further, between the piezoelectric elements 52, support columns 54 are provided corresponding to the partition walls 41 a between the pressurizing chambers 46 and 46. Here, the piezoelectric element member is divided into comb teeth by performing slit processing by half-cut dicing, and each piezoelectric element 52 is formed as a piezoelectric element 52 and a column portion 54. The column portion 54 has the same configuration as that of the piezoelectric element 51, but is a simple column because no driving voltage is applied.
[0028]
Further, the outer peripheral portion of the diaphragm 42 is joined to the frame member 44 by an adhesive 50 including a gap material. The frame member 44 is formed with a recess serving as a common liquid chamber 48 and an ink supply hole (not shown) for supplying ink to the common liquid chamber 48 from the outside. The frame member 44 is formed of, for example, an epoxy resin or polyphenylene sulfite by injection molding.
[0029]
Here, the channel plate 41 is formed by, for example, anisotropically etching a single crystal silicon substrate having a crystal plane orientation (110) using an alkaline etching solution such as an aqueous potassium hydroxide solution (KOH), so that the nozzle communication path 45a, The pressurization chamber 46 and the ink supply passage 47 are formed with recesses and holes. However, the pressurization chamber 46 and the ink supply path 47 are not limited to single crystal silicon substrates, and other stainless steel substrates, photosensitive resins, and the like can also be used.
[0030]
The vibration plate 42 is formed of a nickel metal plate, and is manufactured by, for example, an electroforming method (electroforming method). Other metal plates, resin plates, or a joining member between a metal and a resin plate, or the like may be used. It can also be used. This diaphragm 42 forms a thin part (diaphragm part) 55 for facilitating deformation and a thick part (island-like convex part) 56 for joining with the piezoelectric element 52 in a part corresponding to the pressurizing chamber 46. At the same time, a thick portion 57 is formed at a portion corresponding to the column portion 54 and a joint portion with the frame member 44, the flat surface side is adhesively joined to the flow path plate 41, and the island-like convex portion 56 is joined to the piezoelectric element 52. Further, the thick portion 57 is joined to the support portion 54 and the frame member 44 with the adhesive 50. Here, the diaphragm 42 is formed by nickel electroforming with a two-layer structure. In this case, the diaphragm portion 55 has a thickness of 3 μm and a width of 35 μm (one side).
[0031]
The nozzle plate 43 forms a nozzle 45 having a diameter of 10 to 35 μm corresponding to each pressurizing chamber 46 and is bonded to the flow path plate 41 with an adhesive. The nozzle plate 43 may be made of a metal such as stainless steel or nickel, a combination of a metal and a resin such as a polyimide resin film, silicon, or a combination thereof. Here, it forms with the Ni plating film | membrane etc. by the electroforming method. Further, the inner shape (inner shape) of the nozzle 43 is formed in a horn shape (may be a substantially columnar shape or a substantially frustum shape), and the hole diameter of the nozzle 45 is approximately 20 to 20 on the ink droplet outlet side. 35 μm. Furthermore, the nozzle pitch of each row was 150 dpi.
[0032]
Further, a water repellent treatment layer (not shown) subjected to a water repellent surface treatment is provided on the nozzle surface (surface in the ejection direction: ejection surface) of the nozzle plate 43. Examples of the water-repellent treatment layer include PTFE-Ni eutectoid plating, fluororesin electrodeposition coating, vapor-deposited fluororesin (e.g., fluorinated pitch), silicon resin / fluorine resin A water-repellent treatment film selected according to the ink physical properties such as baking after solvent application is provided to stabilize the ink droplet shape and flying characteristics so that high-quality image quality can be obtained.
[0033]
The piezoelectric element 52 includes a lead zirconate titanate (PZT) piezoelectric layer 61 having a thickness of 10 to 50 μm / layer, and an internal electrode layer 62 made of silver and palladium (AgPd) having a thickness of several μm / layer. The internal electrodes 62 are alternately stacked, and are electrically connected to the individual electrodes 63 and the common electrode 64 which are the end face electrodes (external electrodes) of the end face alternately. The pressurizing chamber 46 is contracted and expanded by expansion and contraction of the piezoelectric element 52 whose piezoelectric constant is d33. The piezoelectric element 52 expands when a drive signal is applied and is charged, and contracts in the opposite direction when the charge charged in the piezoelectric element 52 is discharged.
[0034]
Note that the end face electrode on one end face of the piezoelectric element member is divided by a dicing process by half-cut to be an individual electrode 63, and the end face electrode on the other end face is not divided by a process such as a notch and is divided by all the piezoelectric elements 52. The common electrode 64 becomes conductive.
[0035]
An FPC cable 65 is connected to the individual electrode 63 of the piezoelectric element 52 by solder bonding, ACF (anisotropic conductive film) bonding, or wire bonding in order to give a drive signal, and each piezoelectric element 52 is connected to the FPC cable 65. A drive circuit (driver IC) for selectively applying a drive waveform is connected. The common electrode 64 is connected to the ground (GND) electrode of the FPC cable 65 by providing an electrode layer at the end of the piezoelectric element and turning it around.
[0036]
In the ink jet head configured as described above, for example, by applying a drive waveform (pulse voltage of 10 to 50 V) to the piezoelectric element 52 in accordance with a recording signal, displacement in the stacking direction occurs in the piezoelectric element 52 and vibration occurs. Ink in the pressurizing chamber 46 is pressurized through the plate 42 to increase the pressure, and ink droplets are ejected from the nozzle 45.
[0037]
Thereafter, the ink pressure in the pressurizing chamber 46 decreases with the end of ink droplet ejection, and a negative pressure is generated in the pressurizing chamber 46 due to the inertia of the ink flow and the discharge process of the drive pulse, and the ink filling process is started. Transition. At this time, ink supplied from an ink tank (not shown) flows into the common liquid chamber 48 and is filled from the common liquid chamber 47 through the ink supply port 49 through the fluid resistance portion 47 into the pressurizing chamber 46.
[0038]
The fluid resistance portion 47 is effective in damping residual pressure vibration after ejection, but is resistant to refilling due to surface tension. By appropriately selecting the fluid resistance value of the fluid resistance unit 47, it is possible to balance the attenuation of the residual pressure and the refill time, and to shorten the time (drive cycle) until the transition to the next ink droplet ejection operation.
[0039]
Next, an outline of the control unit of the ink jet recording apparatus will be described with reference to FIGS. FIG. 6 is an overall block diagram of the control unit, and FIG. 7 is a block diagram of a portion related to head drive control of the control unit according to the first embodiment of the present invention.
[0040]
This control unit includes a printer controller 70, a motor driver 81 for driving the main scanning motor 17 and the sub-scanning motor 18, and a head driver (head driving circuit, driver IC for driving the recording head 14 (inkjet head)). 82) and the like.
[0041]
The printer controller 70 includes an interface (hereinafter referred to as “I / F”) 72 that receives print data or the like from a host computer or the like via a cable or a network, a main control unit 73 including a CPU and the like, storage of various data, and the like. RAM 74 for performing the processing, ROM 75 storing routines for various data processing, an oscillation circuit 76, a drive signal generating circuit 77 as a drive waveform generating means for generating a drive waveform for the inkjet head 14, and dot pattern data And an I / F 78 for transmitting print data and drive waveforms developed in (bitmap data) to the head driver 82, an I / F 79 for transmitting motor drive data to the motor driver 81, and the like.
[0042]
The RAM 74 is used as various buffers and work memory. The ROM 75 stores various control routines executed by the main control unit 73, font data, graphic functions, various procedures, and the like.
[0043]
The main control unit 73 reads out the print data in the reception buffer included in the I / F 72, converts it into an intermediate code, stores this intermediate code data in an intermediate buffer constituted by a predetermined area of the RAM 74, and reads the read intermediate code The data is developed into dot pattern data using font data stored in the ROM 75 and stored again in different predetermined areas of the RAM 74. Note that when the print data is expanded into bitmap data and transferred to the recording apparatus by the printer driver on the host side, the received bitmap print data is simply stored in the RAM 74.
[0044]
When the dot pattern data corresponding to one row of the recording head 14 is obtained, the main control unit 73 converts the dot pattern data for one row into the clock signal from the oscillation circuit 76 as shown in FIG. In synchronization with CLK, serial data SD is sent to the head driver 82 via the I / F 78, and a latch signal LTA is sent to the head driver 82 at a predetermined timing.
[0045]
As shown in FIG. 7, the drive signal generation circuit 77 includes a ROM (which can also be configured by a ROM 75) storing pattern data of a drive waveform (drive signal) Pv, and drive waveform data read from the ROM. A waveform generation circuit 91 including a D / A converter that performs D / A conversion and an amplifier 92 are included.
[0046]
The head drive circuit 82 latches the shift register 95 that receives the clock signal CLK from the main control unit 73 and the serial data SD that is the print signal, and the register value of the shift register 95 by the latch signal LAT from the main control unit 73. The latch circuit 96 includes a level conversion circuit (level shifter) 97 that changes the output value of the latch circuit 96, and an analog switch array (switch means) 98 that is turned on / off by the level shifter 97.
[0047]
The switch circuit 98 is composed of an array of switches AS1 to ASn for inputting the drive waveform Pv from the drive signal generation circuit 77, and each of the switches AS1 to ASn is a piezoelectric element corresponding to each nozzle of the recording head (inkjet head) 14. 52, respectively.
[0048]
The print data SD serially transferred to the shift register 95 is once latched by the latch circuit 96. The latched print data is boosted to a voltage that can drive the switch of the switch circuit 98 by the level shifter 97, for example, a predetermined voltage value of about several tens of volts, and is supplied to the switch circuit 98 as the switch means.
[0049]
A drive waveform (drive signal) Pv from a drive signal generating circuit 77 is applied to the input side of the switch circuit 98, and a piezoelectric element 52 as pressure generating means is connected to the output side of the switch circuit 98. . Therefore, for example, during a period in which the print data applied to the switch circuit 98 is “1”, a drive pulse obtained from the drive waveform Pv is applied to the piezoelectric element 52, and the piezoelectric element 52 expands and contracts in accordance with the drive pulse. . On the other hand, while the print data applied to the switch circuit 98 is “0”, the supply of drive pulses to the piezoelectric element 52 is cut off.
[0050]
The shift register 95 and the latch circuit 96 are assembled with a logic circuit, and the level conversion circuit 97 and the switch circuit 98 are assembled with an analog circuit.
[0051]
Next, a drive waveform (drive signal) applied to the piezoelectric element 52 generated from the drive signal generation circuit 77 in the ink jet recording apparatus configured as described above will be described with reference to FIG.
[0052]
First, a first example of the drive signal will be described with reference to FIG. This driving signal causes a plurality of ejection driving pulses PD1, PD2, PD3, and PD4 that are output in time series to eject droplets within one printing cycle, and causes a slight vibration in the meniscus to the extent that droplets are not ejected. It includes waveform elements 110a and 110c of a non-ejection drive pulse PDA (see FIG. 9 described later) to be applied.
[0053]
Here, the ejection drive pulses PD1, PD2, PD3, and PD4 are the first signals (first waveform elements) 101a, 102a, 103a, and 104a for expanding the pressure generating chamber 46, and the post-pressures of the first signals. Second signals (second waveform elements) 101b, 102b, 103b, 104b for maintaining the expansion state of the generation chamber 46, and a third signal (third) for contracting the pressure generation chamber 46 after the second signal. the waveform element) 101c, which is a pulse signal including 102c, 103c, and 104c.
[0054]
Accordingly, droplet discharge by each of the discharge drive pulses PD1, PD2, PD3, and PD4 is performed by a pulling method in which the pressure generating chamber 46 is expanded, filled with liquid, contracted and discharged.
[0055]
Further, as shown in FIG. 9, the non-ejection drive pulse PDA is formed by selecting the waveform elements 110 a and 110 c, and the waveform element 110 a serving as a first signal for expanding the pressure generation chamber 46 and the first waveform element 110 a. a second signal 110b for holding the expanded state of the pressure generating chamber 46 after the signal, a pulse signal that includes a waveform element 110c as a third signal for contracting the pressure generating chamber 46 after the second signal is there. Also in this case, the operation is the same as that for striking (however, no droplet is ejected).
[0056]
Then, here, as shown in FIG. 10, a droplet is ejected by selecting the ejection drive pulse PD1, and as shown in FIG. 11, a middle droplet is ejected by selecting the ejection drive pulse PD2, as shown in FIG. As shown, large droplets are ejected by selecting ejection drive pulses PD1, PD2, PD3, and PD4. The medium droplet may be a drive signal including a small droplet ejection driving pulse PD1, and the large droplet may be composed of three ejection driving pulses PD1, PD2, and PD3.
[0057]
In this case, the droplet speed Vj1 of the droplet ejected by the ejection drive pulse PD1, the droplet speed Vj2 of the droplet ejected by the ejection drive pulse PD2, the droplet speed Vj3 of the droplet ejected by the ejection drive pulse PD3, and the ejection drive pulse PD4 The droplet velocity Vj4 of the ejected droplet is set so that the droplet velocity of the droplet ejected by the ejection drive pulse that is slow in time series becomes faster, that is, Vj1 <Vj2 <Vj3 <Vj4. The parameter is set.
[0058]
Thereby, all the droplets can be merged before landing on the recording medium (paper) to form a large droplet.
[0059]
In this way, by smearing all pulses (large, medium, small droplets, non-ejection drive pulses), it is possible to reduce contamination on the nozzle surface during continuous printing. It is possible to improve the problem of injection bending and nozzle down. In addition, when printing is performed with a certain nozzle, a non-ejection drive pulse is applied to other non-printing nozzles. At this time, the printing nozzles are subject to interference from the non-printing nozzles. By applying the non-ejection drive pulse, the nozzle surface is hardly soiled and normal ejection can be performed.
[0060]
Further, when performing gradation recording, as described above, the first gradation value that does not eject a droplet by selecting a non-ejection drive pulse and an ejection drive pulse that is one of a plurality of ejection drive pulses. The second gradation value for selecting the PD1 and ejecting the droplet, and the ejection driving pulse PD2 other than the ejection driving pulse PD1 selected by the second gradation value (or the ejection driving selected by the second gradation value) 2 or more ejection drive pulses including the pulse PD1 may be selected), and a third gradation value for ejecting the droplets and 3 or more including the ejection drive pulse PD2 selected by the third gradation value are selected. By selecting the ejection driving pulses PD1 to PD4, it is possible to select the fourth gradation value for ejecting the droplets.
[0061]
As described above, since all the droplets are used in the fourth gradation value, a large droplet volume Mj can be obtained without waste.
[0062]
Also, as shown in FIG. 12, the time interval Ta1 from the droplet ejection timing by the ejection driving pulse PD1 to the droplet ejection timing by the ejection driving pulse PD2, from the droplet ejection timing by the ejection driving pulse PD2 to the droplet ejection timing by the ejection driving pulse PD3. The time interval Ta2 and the time interval Ta3 from the droplet ejection timing by the ejection driving pulse PD3 to the droplet ejection timing by the ejection driving pulse PD4 are all integral multiples of the natural vibration period Tc of the pressure generating chamber 46. In this example, the time intervals Ta1 = 3Tc, Ta2 = 4Tc, and Ta3 = 3Tc.
[0063]
In this way, when the interval of the ejection timing is set to an integral multiple of the natural vibration period of the pressure generating chamber, a large droplet is formed by merging before landing a plurality of droplets on the paper as in this image forming apparatus. In this case, it is possible to discharge in accordance with the cycle, and stable discharge can be performed.
[0064]
Next, details of the ejection drive pulse PD1 will be described with reference to FIG.
The ejection drive pulse PD1 is generated by expanding the falling pressure generating chamber 46 from the reference potential Vref to the potential Vc and drawing the meniscus, and the expanded state of the pressure generating chamber 46 expanded by maintaining the potential Vc. And a third signal 101c for causing the pressure generation chamber 46 to contract from the potential Vc to the potential Vd and ejecting the liquid droplets, while maintaining the potential Vd. The fourth signal 101d that holds the contracted state of the pressure generating chamber 46 contracted by the application of the signal 101c, and the rising state to the reference potential Vref after the holding state by the fourth signal 101d causes the pressure generating chamber 46 to contract and drop. And a fifth signal 101e for suppressing residual vibration of the meniscus after ejection.
[0065]
Here, the application time Tb of the fourth signal 101d is set in the range of Tc / 4 to 3Tc / 4, where Tc is the natural vibration period of the pressure generating chamber 46. That is, after the droplet discharge, the fifth signal 101e for applying the contraction of the pressure generation chamber 46 after Tc / 4 to 3Tc / 4 and suppressing the residual vibration of the meniscus after the droplet discharge is applied.
[0066]
FIG. 14A is a diagram showing the residual vibration of the meniscus when the fifth signal 101e is applied, and FIG. 14B shows the fourth signal 101d and the fifth signal 101e. It is the figure which showed the residual vibration of the meniscus in the case of not damping | damping by not applying. From this, it can be clearly seen that the residual vibration of the meniscus is more suppressed in FIG.
[0067]
As described above, at least one of the plurality of ejection driving pulses contracts the pressure generation chamber to eject a droplet, and Tc / 4 to 3 Tc / 4 hours have elapsed when the natural vibration period of the pressure generation chamber is Tc. The residual vibration of the meniscus can be quickly suppressed by including a signal that subsequently contracts the pressure generation chamber and suppresses the residual vibration of the meniscus after droplet discharge.
[0068]
Next, details of the ejection drive pulse PD3 will be described with reference to FIG.
The ejection driving pulse PD3 is generated by expanding the falling pressure generating chamber 46 from the reference potential Vref to the potential Vf and expanding the pressure generating chamber 46 expanded by maintaining the potential Vf. And a third signal 103c that causes the pressure generation chamber 46 to contract from the potential Vf to the potential Vg and eject the droplet, and further maintains the potential Vg to maintain the third signal 103g. The fourth signal 103d for maintaining the contracted state of the pressure generating chamber 46 contracted by the application of the signal 103c, and the rising of the pressure generating chamber 46 to the potential Vh after the holding state by the fourth signal 103d is contracted to discharge the droplet. A fifth signal 103e for suppressing the residual vibration of the subsequent meniscus and a sixth signal for maintaining the contracted state of the pressure generation chamber 46 by the fifth signal 103e. And it includes a signal 103f, and a seventh signal 103g for expanding the pressure generating chamber 46 after the sixth signal 103f.
[0069]
Here, the application time Tb of the fourth signal 103d is set within the range of Tc / 4 to 3Tc / 4, where Tc is the natural vibration period of the pressure generating chamber 46. That is, after the droplet discharge, the fifth signal 103e for contracting the pressure generation chamber 46 after Tc / 4 to 3Tc / 4 and suppressing the residual vibration of the meniscus after the droplet discharge is applied.
[0070]
The application time Td of the fifth signal 103e and the sixth signal 103f is set to Tc / 2 when the natural vibration period of the pressure generation chamber 46 is Tc. That is, after the droplet discharge, the fifth signal 103e is applied to contract the pressure generation chamber 46 after Tc / 4 to 3Tc / 4 to suppress the residual vibration of the meniscus after the droplet discharge, and further after Tc / 2. A seventh signal 103g for expanding the pressure generating chamber 46 is applied.
[0071]
FIG. 16A is a diagram showing the residual vibration of the meniscus when the fifth signal 103e and the seventh signal 103g are applied, and FIG. 16B shows the fifth signal 103e. FIG. 10 is a diagram showing residual vibration of a meniscus when vibration is not suppressed without applying a seventh signal 103g. From this, it can be clearly seen that the residual vibration of the meniscus is more suppressed in FIG.
[0072]
As described above, at least one of the plurality of ejection driving pulses contracts the pressure generation chamber to eject a droplet, and Tc / 4 to 3 Tc / 4 hours have elapsed when the natural vibration period of the pressure generation chamber is Tc. The residual vibration of the meniscus can be quickly suppressed by including a signal for contracting the pressure generation chamber later and expanding the pressure generation chamber after Tc / 2 to suppress the residual vibration of the meniscus after droplet discharge.
[0073]
In the above embodiment, the piezoelectric element is assumed to be PZT displaced in the d33 direction, but may be a flexural vibration type PZT. However, the reliability of the element is higher when PZT with d33 direction displacement is used. An ink jet recording apparatus as an image forming apparatus according to the present invention is equipped with a liquid droplet ejection head for ejecting ink droplets. However, the present invention relates to liquid droplets other than ink, for example, a liquid resist for patterning. The present invention can also be applied to an image forming apparatus equipped with a droplet discharge head that discharges a droplet, a droplet discharge head that discharges a gene analysis sample, and the like.
[0074]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, a plurality of ejection drive pulses output in time series for ejecting droplets and a meniscus to such an extent that the droplets are not ejected within one printing cycle. to both the waveform element of the non-ejection drive pulses to provide a slight vibration, a first signal for expanding the pressure generating chamber, after the first signal, a second signal for holding the expanded state of the pressure generating chamber A part of the timing of ejecting the droplets of the ejection drive pulse generated as a drive pulse including the third signal for contracting the pressure generating chamber after the second signal and applied to the nozzle for ejecting the droplets If, because the application timing of the non-ejection driving pulse applied to the non-discharge nozzle which does not eject droplets is configured to overlap, it is rare contaminating the nozzle surface even after continuous printing, soiling of the nozzle face Injection bend caused by And the problem of nozzle down can be improved, and the image quality is improved.
[Brief description of the drawings]
FIG. 1 is a perspective explanatory view showing an example of a mechanism part of an ink jet recording apparatus as an image forming apparatus according to the present invention. FIG. 2 is a side sectional explanatory view of the mechanism part of the recording apparatus. FIG. 4 is a cross-sectional explanatory view along the liquid chamber long side direction of the head for explaining an example of the ink jet head constituting the head. FIG. 4 is a cross-sectional explanatory view along the liquid chamber short side direction of the head. FIG. 6 is a block diagram for explaining an outline of a control unit of the recording apparatus. FIG. 7 is a block diagram of a portion related to head drive control of the control unit. FIG. 8 is a description for explaining drive signals in the image forming apparatus. FIG. 9 is an explanatory diagram for explaining a non-ejection driving pulse. FIG. 10 is an explanatory diagram for explaining a driving signal for ejecting a small droplet. FIG. 11 is an explanatory diagram for explaining a driving signal for ejecting a medium droplet. FIG. 12 shows a drive for discharging a large droplet. FIG. 13 is a diagram for explaining the details of the ejection drive pulse PD1. FIG. 14 is a diagram for explaining the operation of the ejection drive pulse PD1. FIG. 15 is a diagram for explaining the details of the ejection drive pulse PD3. FIG. 16 is an explanatory diagram for explaining the operation of the ejection drive pulse PD3.
DESCRIPTION OF SYMBOLS 13 ... Carriage, 14 ... Recording head, 41 ... Flow path plate, 42 ... Vibration plate, 43 ... Nozzle plate, 45 ... Nozzle, 46 ... Pressure generating chamber, 47 ... Fluid resistance part, 48 ... Common liquid chamber, 52 ... Piezoelectric Element, 77... Drive signal generation circuit.

Claims (6)

A droplet discharge head having a pressure generating chamber with which a nozzle communicates, a pressure generating means for contracting and expanding the volume of the pressure generating chamber, and a drive signal generating means for generating a plurality of drive pulses within one printing cycle. In an image forming apparatus capable of continuously discharging a plurality of droplets from the droplet discharge head within one printing cycle,
Said drive signal generating means 1 in the printing cycle, the non-ejection drive pulses to be supplied to an extent not to eject the plurality of ejection pulse and the droplet to output time series of micro-vibration to the meniscus in order to eject the droplets Both a waveform element , a first signal for expanding the pressure generating chamber, a second signal for maintaining the expanded state of the pressure generating chamber after the first signal, and a second signal, Generating a driving pulse including a third signal for contracting the pressure generating chamber;
Overlap with a part of the timing for ejecting a droplet of the ejection driving pulse applied to the nozzle for discharging droplets, and application timing of the non-ejection driving pulse applied to the non-discharge nozzle which does not eject droplets An image forming apparatus.   2. The image forming apparatus according to claim 1, wherein the first gradation value that does not cause the liquid droplets to be ejected by selecting the non-ejection driving pulse and one of the plurality of ejection driving pulses is selected and the liquid droplets are selected. Two or more ejection drive pulses including a second gradation value for ejecting ink and an ejection drive pulse other than the ejection drive pulse selected by the second gradation value or an ejection drive pulse selected by the second gradation value. A fourth gradation in which droplets are ejected by selecting a third gradation value for selecting and ejecting droplets and three or more ejection driving pulses including the ejection driving pulse selected in accordance with the third gradation value. An image forming apparatus capable of selecting a tone value.   3. The image forming apparatus according to claim 1, wherein a time interval of each droplet discharge timing by the plurality of discharge drive pulses output in time series is an integral multiple of the natural vibration period Tc of the pressure generating chamber. An image forming apparatus.   4. The image forming apparatus according to claim 1, wherein droplets ejected by the plurality of ejection drive pulses output in time series are droplets ejected by a temporally late ejection drive pulse. An image forming apparatus having a high drop speed.   5. The image forming apparatus according to claim 1, wherein at least one of the plurality of ejection driving pulses contracts the pressure generating chamber to eject a droplet, and the natural vibration of the pressure generating chamber is generated. An image forming apparatus, comprising: a signal for suppressing residual vibration of a meniscus after droplet discharge by contracting the pressure generation chamber after elapse of Tc / 4 to 3Tc / 4 time when the period is Tc.   5. The image forming apparatus according to claim 1, wherein at least one of the plurality of ejection driving pulses contracts the pressure generating chamber to eject a droplet, and the natural vibration of the pressure generating chamber is generated. When the period is Tc, the pressure generating chamber is contracted after elapse of Tc / 4 to 3Tc / 4 hours, and the pressure generating chamber is expanded after elapse of Tc / 2 hours to suppress the residual vibration of the meniscus after the liquid droplet is discharged. An image forming apparatus comprising:

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