Liquid discharge device and liquid discharging method

A liquid discharge device and a method of discharging liquid. The liquid discharge device includes a head driver to drive an actuator element to generate force to discharge an ink droplet from a head onto an object to be conveyed, the object to be conveyed moving relative to the head, and a discharge controller. The discharge controller and the method includes computing a first drive cycle according to an amount of relative movement of the object moving relative to a head, adjusting the first drive cycle to a value within a second cycle range different from a first cycle range in which an ink droplet is abnormally discharged from the head, obtaining a second drive cycle as a result of adjustment performed on the first drive cycle, every time the second drive cycle passes one or more times, and adjusting the first drive cycle.

CROSS-REFERENCE TO RELATED APPLICATION

BACKGROUND

Technical Field

Embodiments of the present disclosure relates to a liquid discharge device and a liquid discharging method.

Background Art

Conventionally, liquid discharge devices such as image forming apparatuses using a head such as an inkjet head are known in the art. In the liquid discharge device as described above, when an actuator element such as a piezoelectric element is driven to eject an ink droplet such as ink, the entire inkjet head or a part of the structure may resonate to cause an unstable ejection state, or the ejection speed of the ink droplet may change to deteriorate image quality. This may be due to the fact that the structural resonance frequency of the inkjet head matches or is close to the drive frequency of the inkjet head, i.e., the frequency at which ink is discharged from the nozzles.

In order to handle such a situation, technologies are known in the art in which a frequency specifying unit that specifies a frequency that affects the resonance of the nozzle based on the vibration waveform detected by a vibration detecting unit that detects the vibration of the actuator element and a shape of the generated driving signal is changed based on the specified frequency to correct frequency characteristics, in order to prevent the occurrence of crosstalk due to the resonance of the nozzle in consideration of changes over time and individual differences of the ink droplet ejection apparatus that ejects ink droplets from the nozzle by a drive waveform composed of a plurality of driving pulses within one print cycle.

SUMMARY

Embodiments of the present disclosure described herein provide a liquid discharge device and a method of discharging liquid. The liquid discharge device includes a head driver configured to drive an actuator element to generate force to discharge an ink droplet from a head onto an object to be conveyed, the object to be conveyed moving relative to the head, and a discharge controller. The discharge controller and the method includes computing a first drive cycle according to an amount of relative movement of an object to be conveyed moving relative to a head, adjusting the first drive cycle to a value within a second cycle range different from a first cycle range in which an ink droplet is abnormally discharged from the head, obtaining a second drive cycle as a result of adjustment performed on the first drive cycle, every time the second drive cycle passes one or more times, adjusting the first drive cycle such that a difference between an accumulated value of the first drive cycle of a prescribed number of consecutive times and an accumulated value of the second drive cycle of a prescribed number of consecutive times does not exceed a permissible value, and driving an actuator element that generates force to discharge an ink droplet from the head onto the object to be conveyed in the second driving cycle.

DETAILED DESCRIPTION

In describing example embodiments shown in the drawings, specific terminology is employed for the sake of clarity. However, the present disclosure is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have the same structure, operate in a similar manner, and achieve a similar result.

An image forming apparatus provided with a liquid discharge device and a liquid discharging method according to an embodiment of the present disclosure is described below with reference to the accompanying drawings. However, no limitation is indicated thereby, and various applications and modifications may be made without departing from the scope of the invention. In the drawings, like reference signs denote like elements, and overlapping description may be simplified or omitted as appropriate.

FIG.1is a diagram illustrating an image forming apparatus that serves as a liquid discharge device, according to the present embodiment.

The image forming apparatus according to the present embodiment includes a main structural frame1, a feed tray2attached to the main structural frame1to store sheets of paper, and an output tray3that is provided for the main structural frame1in a detachable manner stores a sheet of paper on which an image has been formed. The sheet of paper is an example of an object to be conveyed. An ink is an example of liquid, and the drop of ink that is discharged onto the sheet of paper is an example of an ink droplet discharged onto the sheet of paper that serves as an object to be conveyed. Further, the image forming apparatus according to the present embodiment is provided with a cartridge case4that accommodates ink cartridges10k,10c,10m, and10y. The cartridge case4is located on one end side of the front of the main structural frame1. In other words, the cartridge case4is adjacent to the feed tray and the output tray. The cartridge case4protrudes from the front of the main structural frame1and its top face is lower than the top face of the main structural frame1. The cartridge case4is provided with an operation and display unit5on the top face, and the operation and display unit5has, for example, operation keys and indicators.

For example, the ink cartridges10k,10c,10m, and10ythat contain black (K) ink, cyan (C) ink, magenta (M) ink, and yellow (Y) ink, respectively, can be inserted into the cartridge case4from the front side of the main structural frame1toward the rear side. Moreover, the cartridge case4is provided with an openable and closable cartridge cover6on the front side. The cartridge cover6is a front cover that is opened when some of the ink cartridges10k,10c,10m, and10yis attached or detached.

On the operation and display unit5, remaining-amount indicators11k,11c,11m, and11yof the respective colors are arranged. The positions of the remaining amount indicators11k,11c,11m, and11ycorrespond to the positions of the ink cartridges10k,10c,10m, and10yof the respective colors to indicate that the remaining amount of at least one of the ink cartridges is zero or almost zero. Further, the operation and display unit5includes a power switch12, a feed resume or print resume key13, and a cancellation key14that are arranged on the top face of the operation and display unit5.

FIG.2is a schematic diagram illustrating a mechanical section of the image forming apparatus according to the present embodiment.

FIG.3is a schematic plan view of a mechanical section of the image forming apparatus according to the present embodiment.

In the present embodiment, a carriage23is slidably held in the main scanning direction by a guide rod21and a stay22that are guide units laterally bridged between right and left side plates. The carriage23performs scanning while being moved by a main-scanning motor24in the directions indicated by an arrow, through a timing belt27laid across and stretched between a drive pulley25and a driven pulley26.

On the carriage23, recording heads31k,31c,31m, and31yas heads (inkjet heads) for ejecting ink droplets of the respective colors described above are mounted such that a plurality of ink ejection ports are arranged in a direction intersecting the main scanning direction and the ink droplet ejection direction is directed downward.

As the inkjet head, for example, a head including a piezoelectric actuator such as a piezoelectric element, a thermal actuator using a phase change due to film boiling of liquid using an electrothermal conversion element such as a heating resistor, as an actuator element that generates force to discharge ejecting ink droplets, can be used. In addition to the above, for example, a shape-memory alloy actuator using metal phase change due to temperature change, an electrostatic actuator using electrostatic force, can be used as an actuator element.

The inkjet head may have a configuration in which a plurality of nozzle rows are provided by arranging a plurality of nozzles, and droplets of the same color are discharged from each nozzle row, or may have a configuration in which droplets of different colors are discharged. Moreover, a plurality of head tanks32of the respective colors that supply the inks of the respective colors to the recording heads31k,31c,31m, and31yare mounted on the carriage23.

The head tank32is supplied with ink of each color from the ink cartridges10k,10c,10m, and10yof each color mounted on the cartridge case4through the ink supply tube of each color. On the other hand, the feed roller43and a separation pad44are provided as a sheet feeder that feeds the sheet of paper42stacked on the sheet stacking portion41of the feed tray2. The feed roller43separates and feeds the sheet of papers42on a one-piece-by-one-piece basis from the sheet stacking portion41. The separation pad44is made of a material having a large friction coefficient, faces the feed roller43, and is biased toward the feed roller43.

The image forming apparatus according to the present embodiment includes a guide unit45that guides the sheet of paper42, a counter roller46, a conveyance guide unit47, and a pressing member48provided with a leading-end pressure roller49. With this configuration, the sheet of paper42that is fed from the sheet feeder is fed to the lower side of the recording heads31k,31c,31m, and31y. The image forming apparatus according to the present embodiment further includes a conveyance belt51that electrostatically attracts the fed sheet of paper42and conveys it at a position facing the recording heads31k,31c,31m, and31y.

The conveyance belt51is an endless belt stretched between the conveyance roller52and the tension roller53and goes around in the conveyance direction of the belt. In other words, the conveyance belt51goes around in the sub-scanning direction. The conveyance belt51has a surface layer serving as a paper attracting surface and a back layer made of the same material as the surface layer and having resistance controlled by carbon. The surface layer is formed of, for example, a pure resin material having a thickness of about 40 micrometers (μm) without resistance control, for example, an ethylene tetrafluoroethylene (ETFE) pure material, and the back layer is formed of, for example, a medium-resistance layer or a ground layer.

The image forming apparatus according to the present embodiment includes a charging roller56that serves as a charger to charge a surface of the conveyance belt51. The charging roller56is arranged so as to contact the surface layer of the conveyance belt51and to rotate a driven by the rotation of the conveyance belt51and applies prescribed pressing force through both ends of the axis.

The conveyance roller52also serves as a ground roller, and is disposed in contact with the medium-resistance layer of the conveyance belt51and grounded. A guide unit57is disposed on the rear side of the conveyance belt51so as to correspond to the printing areas of the recording heads31k,31c,31m, and31y.

The guide unit57is projected to the recording head35side from a tangent line of two rollers including a conveyance roller52and a tension roller53whose top faces support the conveyance belt51. Due to such a configuration, the highly accurate flatness or smoothness of the conveyance belt51is maintained. The conveyance roller52is rotationally driven by the sub-scanning motor58via the drive belt59and the pulley60, so that the conveyance belt51moves in the belt conveyance direction inFIG.3, that is, in the sub-scanning direction.

Further, as a sheet ejection unit for discharging the paper42recorded by the recording heads31k,31c,31m, and31y, a separation claw61for separating the paper42from the conveyance belt51, a output roller pair62, and a output roller pair63are provided, and the output tray3is provided below the output roller pair62.

A double-sided unit71is attached to the rear side of the main structural frame1in a detachable manner. The double-sided unit71takes in the sheet of paper42returned by the reverse rotation of the conveyance belt51, and reverses it to feeds the sheet of paper42again to the nip between the counter roller46and the conveyance belt51. Moreover, the upper side of the double-sided unit71serves as a manual sheet feeding tray72.

Further, as illustrated inFIG.3, a maintenance-and-recovery unit81that maintains and recovers the state of the nozzles of the recording heads31k,31c,31m, and31yis disposed in a non-print area on one side of the pair of scanning directions of the carriage23. The maintenance-and-recovery unit81includes, for example, a plurality of caps82ato82d, a wiper blade83, and a dummy discharge receptacle84.

The caps82ato82dcap the faces of the multiple nozzle plates of the recording heads31k,31c,31m, and31y. The wiper blade83is a blade used to wipe the face of a nozzle plate. The dummy discharge receptacle84receives droplets when dummy discharge is performed to discharge droplets that have no influence on recording in order to discharge the thickened recording liquid. In the present embodiment, the cap82ais a suction and moisture-retentive cap, and the other caps82bto82dare moisture-retentive caps. The cap82amay be referred to as a suction cap in the following description.

In a non-print area on the other side in the scanning direction of the carriage23, a dummy discharge receptacle88is arranged for receiving ink droplets when dummy discharge is performed for ejecting ink droplets not contributing to recording in order to discharge the recording liquid that is thickened during, for example, the recording operation. The dummy discharge receptacle88is provided with openings89ato89din the column direction of the nozzles of the recording heads31k,31c,31m, and31y.

In the ink jet recording apparatus configured as described above, the sheet of paper42is separately fed from the feed tray2on a one-piece-by-one-piece basis, and the sheet of paper42that is fed substantially vertically upward is guided by a guide unit45. Then, the sheet of paper42is nipped between the conveyance belt51and the counter roller46and is conveyed. Further, the leading end of the sheet of paper42is guided by a conveyance guide, and the sheet of paper42is pressed against the conveyance belt51by the leading-end pressure roller49to change the conveyance direction by approximately 90 degrees.

In so doing, positive power and negative power, i.e., alternating voltage, are alternately and repeatedly output and applied from an alternating-current (AC) bias supply unit to the charging roller56by a control circuit, and the conveyance belt51attains an alternating charged-voltage pattern. In other words, the conveyance belt51is alternately charged with the positive and negative in a belt-like manner with a prescribed width in a sub-scanning direction, i.e., the rotating direction.

Once the sheet of paper42is fed onto the conveyance belt51that is alternately charged with positive and negative voltages, the sheet of paper42adheres to the conveyance belt51, and the sheets of paper42conveyed in the sub-scanning direction as the conveyance belt51moves and goes around. Then, the recording heads31k,31c,31m, and31yare driven according to the image signals while the carriage23is being moved. In so doing, ink droplets are discharged to the sheet of paper42at a standstill to record a single line of the image. Then, the sheet of paper42is conveyed in a prescribed amount, and the next line of the image is recorded.

Once a recording end signal or a signal indicating that a trailing end of the sheet of paper42has reached a recording area is received, the recording operation is terminated, and the sheet of paper42is ejected to the output tray3. While the system is on standby waiting for next printing operation, the carriage23is moved to the maintenance-and-recovery unit81side, and the recording heads31k,31c,31m, and31yare capped by the caps82a,82b,82c, and82d. Accordingly, the nozzles can be kept moist or wet, and the failure of discharge due to dried ink can be prevented.

Moreover, in a state where the recording heads31k,31c,31m, and31yare capped by the caps82a,82b,82c, and82d, respectively, a recovery operation is performed in which the recording liquid is sucked from the nozzles by a suction pump and the thickened recording liquid or air bubbles are discharged. For example, before the start of recording or during the recording, a dummy discharge operation is performed to discharge ink unrelated to recording toward the dummy discharge receptacles84and88. In other words, ink droplets that do not contribute to image formation are discharged. By so doing, stable discharging performance of the recording heads31k,31c,31m, and31ycan be maintained or recovered.

FIG.4is a sectional view of the liquid discharge head31that serves as a recording head of the image forming apparatus, parallel to the longer-side direction of a liquid chamber, according to the present embodiment.

FIG.5is a sectional view of the liquid discharge head31of the image forming apparatus, parallel to the shorter-side direction of a liquid chamber, according to the present embodiment.

In the liquid discharge head31, a channel substrate101, a vibration plate102, and a nozzle plate103are bonded and stacked, so as to form, for example, a nozzle communication channel105and a liquid chamber106which serves as a duct through which a nozzle104communicates to discharge ink droplets, an ink supply port109that communicates with a common chamber108used to supply the liquid chamber106with ink.

The channel substrate101is formed by etching, for example, a steel special use stainless (SUS) substrate or a single-crystal silicon substrate. The vibration plate102is formed by, for example, nickel electroforming bonded to the bottom side of the channel substrate101. The nozzle plate103is bonded to the top surface of the channel substrate101.

Moreover, as an actuator element that serves as a pressure generator used to deform the vibration plate102to pressurize the ink in the liquid chamber106, two rows of multi-layered piezoelectric elements121and a base substrate122that bonds and fixes the piezoelectric elements121are provided. A support portion123is provided for the two rows of the piezoelectric elements121. The support portion123is formed at the same time as the piezoelectric elements121by dividing a component of the piezoelectric element. However, no driving voltage is applied to the support portion123, and thus the support portion123is simply a columnar object.

Moreover, a flexible printed circuit (FPC) cable126that is connected to a driver integrated circuit (IC) is coupled to the piezoelectric elements121. Further, a peripheral portion of the vibration plate102is bonded to the frame member130.

A penetrating portion131and an ink feed hole132are formed through the frame member130. The penetrating portion131accommodates an actuator unit composed of, for example, the piezoelectric elements121and the base substrate122. The common chamber108and a concave portion that turns to become the common chamber108are supplied with ink externally through the ink feed hole132. The frame member130is formed by injection molding using polyphenylene sulfite or thermosetting resin such as epoxide-based resin.

In the present embodiment, for example, the channel substrate101is formed by anisotropic etching in which a single-crystal silicon substrate having a crystal face orientation [110] is etched with an alkaline etching solution such as potassium hydroxide solution (KOH). Alternatively, the channel substrate101may be formed by etching a steel special use stainless (SUS) substrate. As a result, the nozzle communication channel105, a concave portion that turns to become the liquid chamber106, or a through-hole are formed.

The vibration plate102is made of a metal plate of nickel, and is formed by, for example, electroforming. However, no limitation is indicated thereby, and the vibration plate102may be formed using, for example, a metal plate, a combination of metal and resin plate. The piezoelectric elements121and the support portion123are bonded to the vibration plate102using an adhesive, and the frame member130is further bonded to the vibration plate102using an adhesive.

The nozzle plate103forms a nozzle104having a diameter of 10 to 30 μm corresponding to each liquid chamber106, and is bonded to the channel substrate101with an adhesive. The nozzle plate103is formed by forming a water-repellent layer on the outermost surface of a nozzle forming member made of a metal member, having a prescribed layer therebetween. The surface of the nozzle plate103serve as face31athe nozzle plate.

The piezoelectric elements121is a multi-layered piezoelectric element in which a piezoelectric material151and an internal electrode152are alternately stacked on top of each other. An individual electrode153and a common electrode154are connected to each internal electrode152pulled out to alternately different end faces of the piezoelectric elements121.

In the present embodiment, the ink that is kept inside the liquid chamber106is pressurized using the shift in d33 direction as the piezoelectric direction of the piezoelectric elements121. However, no limitation is indicated thereby, and the ink that is kept inside the liquid chamber106may be pressurized using the shift in d31 direction as the piezoelectric direction of the piezoelectric elements121. Alternatively, one row of piezoelectric element121may be arranged on one base substrate122.

In the liquid discharge head according to the present embodiment as described above, for example, as the voltage applied to the piezoelectric elements121is lowered from the reference potential, the piezoelectric elements121contracts, the vibration plate102descends, and the volume of the liquid chamber106expands. As a result, ink flows into the liquid chamber106.

Then, the voltage applied to the piezoelectric elements121is increased to extend the piezoelectric elements121in the stacking direction, and the vibration plate102is deformed toward the nozzle104to reduce the size or volume of the liquid chamber106. As a result, the recording liquid in the liquid chamber106is pressurized, and a drops of the recording liquid are discharged from the nozzle104.

As the voltage applied to the piezoelectric elements121is returned to a reference potential, the vibration plate102is restored to the initial position, and the liquid chamber106expands. As a result, negative pressure is generated. Accordingly, the liquid chamber106is filled with the recording liquid from the common chamber108. Accordingly, the vibration of the meniscus face of the nozzle104is attenuated and stabilized. Then, the operation shifts to the next droplet discharge operation.

The method of driving the head is not limited to the above-described example of the pull-and-push driving, and for example, the pull-and-push driving can also be performed depending on how the driving waveform is applied.

FIG.6is a schematic diagram illustrating the controllers of an image forming apparatus, according to the present embodiment.

The controller according to the present embodiment includes a main controller301and a print controller302. The main controller301is constituted by a microcomputer serving also as a unit for controlling the entire image forming apparatus and performing control related to the dummy discharge operation according to the present invention. The print controller302is configured by a microcomputer or microprocessor that manages the printing operation. The print controller302corresponds to the discharge controller.

The main controller301performs control as follows to form an image on the sheet of paper42based on the print data input from the communication circuit300. For example, the main-scanning motor24is controlled through the main-scanning motor driver303, and the sub-scanning motor58is controlled through the sub-scanning motor driver304. Moreover, print data may be sent to the print controller302in the above control performed by the main controller301.

Moreover, the main controller301receives a detection signal from a carriage position detector305that detects the position of the carriage23. The main controller301controls the moving position and the moving speed of the carriage23based on the received detection signal.

For example, the carriage position detector305causes a photodetector provided for the carriage23to read and count the number of slits of an encoder sheet arranged in the scanning direction of the carriage23, to detect the position of the carriage23.

The main-scanning motor driver303rotationally drives the main-scanning motor24in accordance with the amount of movement of the carriage23, which is input from the main controller301, to move the carriage23to a prescribed position at a prescribed speed.

The main controller301receives a detection signal from a carriage position detector306that detects the amount of movement of the conveyance belt51. The main controller301controls the moving amount and the moving speed of the conveyance belt51based on the detection signal.

For example, the carriage position detector306causes a photodetector to read and count the number of slits of a rotary encoder sheet attached to the rotation axis of the conveyance roller52, to detect the amount of conveyance.

The sub-scanning motor driver304drives the sub-scanning motor58to rotate according to the amount of conveyance input from the main controller301, and drives the conveyance roller52to rotate to move the conveyance belt51to a prescribed position at a prescribed speed.

The main controller301according to the present embodiment provides the feed roller driver307with a feed roller drive command to rotate the feed roller43one time. The main controller301according to the present embodiment causes the maintenance-and-recovery unit motor driver308to rotate the motor221of the maintenance-and-recovery unit81. As a result, as described above, the caps82a,82b,82c, and82dare moved up and down, and the wiper blade83is moved up and down. Moreover, for example, the suction pump is driven.

The main controller301according to the present embodiment controls the operation of the ink supply motor that drives the pump of the supply unit through an ink supply motor driver311. According to such a configuration, ink is supplied from the ink cartridges10k,10c,10m, and10yinserted into the cartridge case4to the head tank32. At that time, the main controller301detects that the head tank32is filled up. The supplying and filling operation is controlled based on a detection signal sent from a head tank fill-up sensor312.

The main controller301according to the present embodiment causes a cartridge communication circuit314to obtain the data stored in a cartridge electrically erasable and programmable read only memory (EEPROM)316provided for each one of the ink cartridges10k,10c,10m, and10yaccommodated in the cartridge case4. Then, for example, the main controller301performs a required process and caused the EEPROM315to store the obtained data.

Further, a detection signal from an environment sensor313that detects an environmental temperature and an environmental humidity is input to the main controller301.

The print controller302generates data used to drive the pressure generator that causes the recording heads31k,31c,31m, and31yto discharge ink droplets based on a signal sent from the main controller301and the carriage position and the amount of conveyance sent from, for example, the carriage position detector305and the carriage position detector306. The print controller302transfers the generated data to the head driver310as serial data, and outputs, for example, a transfer clock, a latch signal, a mask signal as a drop control signal, which are used to transfer the data or determine the transfer, to the head driver310.

Moreover, the print controller302includes a digital-to-analog (D/A) converter that performs digital-to-analog (D/A) conversion on the pattern data of the driving signals stored in a read only memory (ROM), a drive waveform generation unit, and a selector that selects a drive waveform to be given to a head driver. The drive waveform generation unit includes, for example, a voltage amplifier and a current amplifier. The print controller302generates a drive waveform including a plurality of driving signal groups each including one driving pulse or a plurality of driving pulses, which are driving signals, and outputs the drive waveform to the head driver310.

The head driver310is a driver that supplies each one of the recording heads31k,31c,31m, and31ywith a driving signal. More specifically, the head driver310drives the recording heads31k,31c,31m, and31yby selectively applying a driving signal to the driving elements of the recording heads31k,31c,31m, and31ybased on prescribed image data.

The prescribed image data is, for example, image data corresponding to a single line of the recording heads31k,31c,31m, and31ythat are serially input. The driving signal makes up a drive waveform given from the print controller302. The driving element is, for example, a piezoelectric element as described above that is provided for each one of the recording heads31k,31c,31m, and31yto generate energy to discharge ink droplets.

In so doing, the driving pulse is selected from the driving signal groups that make up the drive waveform. As a result, ink droplets having different sizes can be discharged to print dots with different sizes separately.

FIG.7is a diagram illustrating the print controller302and the head driver310, according to the present embodiment.

The print controller302according to the present embodiment includes a drive cycle computation unit400, a drive waveform generation unit401, and a data transfer unit402. The drive cycle computation unit400calculates a drive cycle. The drive waveform generation unit401generates and outputs a drive waveform, i.e., a common drive waveform. The data transfer unit402outputs 2-bit image data, i.e., gradation signals 0 and 1, corresponding to a print image, a clock signal, a latch signal, and drop control signals MN0to MN3.

The drive cycle computation unit400computes the driving cycle based on the reading time interval of the slit of the encoder sheet by the carriage position detector305, i.e., the amount of relative movement of the sheet. Then, the drive cycle computation unit400outputs the drive cycle obtained by the above calculation to the drive waveform generation unit401, and causes the data transfer unit402to output various types of signals such as latch signals in the drive cycle obtained by the above calculation. How the drive cycle is calculated will be described later in detail.

The drive waveform generation unit401generates a drive waveform including two or more driving signals in one drive cycle. More specifically, as will be described later in detail with reference toFIG.8A, the drive waveform generation unit401generates and outputs a drive waveform continuously including a first driving signal group PG1including one or more driving signals and a second driving signal group PG2including one or more driving signals in one drive cycle. In the present embodiment, an example in which the number of driving signal groups is two is described. However, no limitation is indicated thereby, and a configuration in which three or more driving signal groups are generated and output may be employed.

The data transfer unit402continuously outputs the drop control signals MN0to MN3for selecting the driving signal from the first driving signal group PG1and the second driving signal group PG2within one drive cycle, in view of the outputs from the first driving signal group PG1and the second driving signal group PG2.

The drop control signals MN0to MN3are 2-bit signals used to instruct an analog switch415, which is a switching unit of the head driver310, to open and close. The drop control signals MN0to MN3make a state transition to the L level with a waveform to be selected in accordance with the cycle of the first driving signal group PG1and the second driving signal group PG2, and make a state transition to the H level when no waveform is selected.

The head driver310according to the present embodiment includes a shift register411, a latch circuit412, a decoder413, a level shifter414, and an analog switch415.

The shift register411receives from the data transfer unit402a shift clock as a transfer clock and gradation data (2 bits/CH) as serial image data. The latch circuit412latches each register value of the shift register411by a latch signal. The decoder413decodes the gray-scale data and the first and second drop control signals MN0ato MN3aand MN0bto MN3b, and outputs the result of decoding.

The level shifter414converts the logic-level voltage signal of the decoder413into a level at which the analog switch415can operate. The analog switch415is turned on and off by the output of the decoder413supplied through the level shifter414. The analog switch415is coupled to one of the individual electrodes153, which is the electrode selected by one of the multiple piezoelectric elements121, and receives a common drive waveform from the drive waveform generation unit401.

The analog switch415is turned on according to the serially transferred image data and the result of decoding of the drop control signals MN0to MN3by the decoder413. As a result, required driving signals constituting the first driving signal group PG1and the second driving signal group PG2included in the common drive waveform are selected pass through, and are applied to the piezoelectric elements121.

FIG.8AandFIG.8Bare schematic diagrams each illustrating a drive waveform and a drop control signal used to select a driving signal that are generated and output by the drive waveform generation unit included in the print controller302, according to the present embodiment.

FIG.9is a schematic diagram illustrating the amount of drop to be discharged indicated by a drop control signal, according to the present embodiment.

By way of example, the drive waveform output from the drive waveform generation unit401and the drop control signal output from the data transfer unit402are described below with reference toFIG.8A,FIG.8B, andFIG.9. As illustrated inFIG.8A, the first driving signal group PG1output from the drive waveform generation unit401includes a non-discharge driving pulse P1and discharge driving pulses P2and P3.

The non-discharge driving pulse P1consists of a waveform element falling from the reference potential, a waveform element held at the potential of falling edge, and a waveform element continuously rising to the post-hold reference potential. Each of the discharge driving pulse P2and the discharge driving pulse P3consists of a waveform element falling from the reference potential, a waveform element held at the potential of falling edge, and a waveform element gradually rising to the post-hold reference potential.

The non-discharge driving pulse indicates a driving pulse that drives the piezoelectric elements121but only gives vibration to the meniscus and does not discharge any ink droplet from the nozzle. The discharge driving pulse indicates a driving pulse used to drive the piezoelectric elements121to discharge an ink droplet from the nozzle.

The second driving signal group PG2, which is generated and output continuous to the first driving signal group PG1, consists of a discharge driving pulse P4and a discharge driving pulse P5. The discharge driving pulse P4consists of a waveform element falling from the reference potential, a waveform element held at the potential of falling edge, and a waveform element continuously rising to the post-hold reference potential.

The discharge driving pulse P5consists of a waveform element falling from the reference potential, a waveform element held at the potential after the falling edge, a waveform element continuously rising to a potential higher than the post-hold reference potential, a waveform element held at the potential after the rising edge, and a waveform element falling to the post-hold reference potential.

In the present embodiment, the waveform element in which the potential V of the driving pulse falls from the reference potential Ve is a pull-in waveform element in which the piezoelectric elements121contracts and the volume of the pressurized liquid chamber106expands. Moreover, the waveform element that rises from the state after the fall is a pressurizing waveform element in which the piezoelectric elements121expands and the volume of the pressurizing liquid chamber106contracts.

In regard to the above drive waveform, as illustrated inFIG.8B, the data transfer unit402sequentially outputs drop control signals MN0to MN3used to select the driving pulses P1to P3that together configure of the first driving signal group PG1and the driving pulses P4and P5that together configure the second drive waveform group PG2.

In the drop control signals MN0to MN3, as illustrated inFIG.9, when the drop control signal MN0is given, only the driving pulse P1is selected and given to the head. As a result, the driving is to be performed with non-discharge, and the amount of drop to be discharged is 0 pl.

In a similar manner to the above, when the drop control signal MN1is given, only the driving pulse P3is selected and given to the head. As a result, the amount of drop to be discharged is 3 pl. When the drop control signal MN2is given, the driving pulses P2and P4are selected and given to the head, and the amount of drop to be discharged is 9 pl. Further, when the drop control signal MN3is given, the driving pulses P2to P5are selected and given to the head, and the amount of drop to be discharged is 18 pl.

In other words, as the driving pulses P1to P5that form the drive waveform with four kinds of 2-bit drop control signals MN0to MN3are selected, four sizes of drops including non-discharge of 0 pl, a small drop of 3 pl, a medium drop of 9 p], and a large drop of 18 pl can be obtained. In other words, according to the present embodiment, droplets with different sizes can be discharged with a simple configuration.

FIG.10is a schematic diagram illustrating the frequency characteristics of the structural vibration of the recording head, according to the present embodiment.

InFIG.10, the vertical axis indicates the velocity when the amount of deformation of the head nozzle surface during driving of one pressure chamber by sinusoidal wave input is measured by a laser Doppler meter, and the horizontal axis indicates the frequency of driving. The numerical value on the vertical axis corresponds to the amount of deformation of the head, and a larger numerical value indicates a larger amount of deformation of the head.

As is apparent fromFIG.10, with the recording head according to the present embodiment, a large resonance can be observed when the frequency is at 395 kilohertz (kHz). Although other resonances are observed, the peaks of those resonances are not as high as that of 395 kHz. Accordingly, 395 kHz may be considered to be a representative frequency in the present embodiment. If the peak value (resonance frequency) of the frequency of the resonance spectrum or the divisor of the resonance frequency coincides with or is close to the drive frequency (inverse number of the drive cycle) of the inkjet head, structural resonance of the recording head is excited and discharge stability is adversely affected. In other words, ink is abnormally discharged. As a result, the ink ejection accuracy deteriorates.

In order to handle such a situation, in the present embodiment, the drive cycle computation unit400adjusts the drive cycle to a value selected from a range different from a range including the resonance frequency or a frequency of a divisor of the resonance frequency. Accordingly, the precision of ink discharge can be prevented from deteriorating.

A method of calculating a drive cycle using the drive cycle computation unit400will be described below. As described above, the drive cycle computation unit400computes the driving cycle based on the reading time interval of the slit of the encoder sheet by the carriage position detector305, which is the amount of relative movement of the sheet. Then, for example, the drive cycle computation unit400causes the data transfer unit402to output a latch signal to the head driver310in accordance with the calculated drive cycle.

In so doing, the reading time interval of the slit of the encoder sheet may be used as the drive cycle, or a value calculated by computation using the reading time interval of the slit of the encoder sheet may be used as the drive cycle. For example, when the reading time interval is set to a pitch of 150 dots per inch (dpi) and the discharge interval of the ink droplets is set to 300 dpi, the drive cycle computation unit400can set a cycle obtained by multiplying the reading time interval by ½ as the drive cycle. Moreover, in order to remove noise in the drive cycle, the drive cycle computation unit400can take a moving average for a plurality of consecutive drive cycles. The drive cycle that is computed by the processing up to this point is referred to as a before-adjustment drive cycle. The before-adjustment drive cycle corresponds to the first drive cycle.

Moreover, the drive cycle computation unit400adjusts the before-adjustment drive cycle to a value within another cycle range different from the cycle range in which abnormal discharge occurs due to resonance. The cycle range in which abnormal discharge occurs is a cycle range including the resonance frequency or a frequency of a submultiple of the resonance frequency, and corresponds to the first cycle range. The other cycle range that is different from the cycle range in which abnormal discharge occurs corresponds to the second cycle range. The drive cycle after adjustment corresponds to the second drive cycle. Note that the drive cycle after adjustment may be referred to as an after-adjustment drive cycle in the following description.

In order to prevent the landing position of the ink from being significantly displaced from the target position due to the adjustment of the drive cycle, the drive cycle computation unit400determines the value of the after-adjustment drive cycle from within the second cycle range such that the accumulated value of the prescribed number of consecutive after-adjustment drive cycles is approximately equal to the accumulated value of the prescribed number of before-adjustment drive cycles corresponding to the prescribed number of consecutive after-adjustment drive cycles. More specifically, the drive cycle computation unit400determines the value of the after-adjustment drive cycle from within the second cycle range so that the difference between the accumulated value of the prescribed number of consecutive after-adjustment drive cycles and the accumulated value of the prescribed number of consecutive before-adjustment drive cycles corresponding to the prescribed number of consecutive after-adjustment drive cycles does not exceed a permissible value.

More specifically, the drive cycle computation unit400computes a new after-adjustment drive cycle Tafter_cur so as to satisfy the following first condition and second condition.

First Condition
(Tafter_cur>Amax) or (Amin>Tafter_cur)

In the above condition, Amax denotes an upper limit of the cycle range in which abnormal ejection occurs, and Amin denotes a lower limit of the cycle range in which abnormal ejection occurs. SUM (Tbefore) denotes the accumulated value of the latest n consecutive before-adjustment drive cycles Tbefore including the before-adjustment drive cycle Tbefore_cur that is the source of the new after-adjustment drive cycle Tafter_cur, and SUM denotes an operator that indicates accumulation. SUM (Tafter) denotes an accumulated value of the latest n consecutive after-adjustment drive cycles Tafter including the new after-adjustment drive cycle Tafter_cur. N denotes an example of a prescribed number of times, and is a natural number of two or more. Z denotes an example of a permissible value, and is any positive real number.

Some of or all of the inequality signs included in the first condition and the second condition may be an inequality sign with an equal sign.

The drive cycle computation unit400performs adjustment to obtain a before-adjustment drive cycle Tbefore every time the before-adjustment drive cycle Tbefore passes one or more times. In the following description, it is assumed that the drive cycle computation unit400performs adjustment to obtain a before-adjustment drive cycle Tbefore every time the before-adjustment drive cycle Tbefore passes one time.

FIG.11is a graph illustrating the progression of drive cycles computed by the drive cycle computation unit400, according to the present embodiment.

In the present embodiment, the resonance frequencies of the head are around 395 kHz. In such cases, in order to avoid resonance of the structure of the head, it is desired that a drive cycle of a multiple of a period of 2.53 microseconds (p) be avoided. Accordingly, in the drive cycle computation unit400, the cycle range501having a prescribed width including 2.53 μs is set as the first cycle range in which the discharge abnormality occurs due to resonance.

Further, the drive cycle can be set within the cycle range502if the discharge abnormality is not taken into consideration. Accordingly, the cycle range503from which the cycle range501in the cycle range502is excluded is adopted as the second cycle range. The second cycle range is a cycle range in which a discharge abnormality due to resonance is does not occur.

The cycle range502includes the cycle range501. Accordingly, the cycle range503is divided into a cycle range504that contacts the upper limit of the cycle range501and a cycle range505that contacts the lower limit of the cycle range501. The cycle range504corresponds to the third cycle range. The cycle range505corresponds to the fourth cycle range.

The triangular dots represent the progression of the before-adjustment drive cycle. The circular dots represent the progression of the after-adjustment drive cycle. Although the before-adjustment drive cycle is partially included in the cycle range501where the discharge may be performed abnormally, it is interpreted from the graph that the after-adjustment drive cycle is set so as to avoid the cycle range501. In other words, if the after-adjustment drive cycle is used, the structural resonance of the recording head can be prevented, and thus the precision of the ink discharge can be prevented from deteriorating.

The square dots represents five-point moving averages of the after-adjustment drive cycle. It is interpreted fromFIG.11that the five-point moving averages of the after-adjustment drive cycle approximately match the progression of the before-adjustment drive cycle. This is achieved because a sufficiently small value is set as the parameter Z used in the second condition.

The after-adjustment drive cycle is computed by adjusting the value of the before-adjustment drive cycle calculated so as to correspond to the amount of relative movement of the sheet of paper. Accordingly, when a value that deviates from the before-adjustment drive cycle is used as the after-adjustment drive cycle, the position at which ink is to be discharged is locally displaced from the target position. Moreover, the amount of displacement of each drive cycle is accumulated every time the drive cycle has passed. However, as the after-adjustment drive cycle is set so that the moving average of the after-adjustment drive cycle approximately matches the progression of the before-adjustment drive cycle, the amount of displacement of the position at which ink is to be discharged from the target position can be prevented from increasing due to accumulation.

Any real number may be set as the parameter Z. For example, the value obtained by dividing the distance determined according to the target resolution by the relative speed of the sheet of paper with respect to the carriage can be set as the parameter Z. As the parameter Z is determined in view of the target resolution, the influence of the displacement of the position at which ink is to be discharged from the target position on the image quality can be prevented.

In one example, the distance determined in view of the target resolution, which is as described above, may be considered to be half the distance of the intervals at which ink is to be discharged in view of the target resolution. Accordingly, the influence of the displacement of the position at which ink is to be discharged from the target position on the image quality can be reduced to a level such an influence cannot visually be recognized. The distance that determined based on the target resolution is not limited to the above value.

In the example illustrated inFIG.11, the value of an after-adjustment drive cycle is alternately selected from the cycle range504and the cycle range505, for each before-adjustment drive cycle. In other words, the value of the after-adjustment drive cycle is selected from one of the cycle range504and the cycle range505, and then the value of the after-adjustment drive cycle is selected from the other of the cycle range504and the cycle range505. The value of the after-adjustment drive cycle is not selected twice or more continuously from one of the cycle range504and the cycle range505. As the value of the after-adjustment drive cycle is selected in such a manner as described above, the amount of displacement of the position at which ink is to be discharged from the target position can be reduced to a small amount compared with a case in which the selection source of the value of the after-adjustment drive cycle is switched between the cycle range504and the cycle range505every time two or more values of the after-adjustment drive cycle are selected.

The selection source of the value of the after-adjustment drive cycle may be switched between the cycle range504and the cycle range505every time two or more values of the after-adjustment drive cycle are selected.

n may be any natural number equal to or greater than 2. However, as n is smaller, the accumulated amount of displacement of the landing position of the ink from the target position can be reduced to a smaller amount. Accordingly, the influence on image quality can be reduced.

FIG.12is a flowchart of the operation of the image forming apparatus according to the present embodiment.

Firstly, in a step S101, the print controller302acquires time the intervals at which the encoder sheet is read from the carriage position detector305. Then, in a step S102, the drive cycle computation unit400computes a new value Tbefore_cur for a before-adjustment drive cycle Tbefore based on the acquired time intervals at which the encoder sheet is read.

As described above, the drive cycle computation unit400may set the reading time interval of the encoder sheet to Tbefore_cur. Alternatively, the drive cycle computation unit400may perform prescribed processing such as division, multiplication, and moving averaging on the reading time interval of the encoder sheet, and may set a value obtained by the processing as Tbefore_cur.

Subsequently, in a step S103, the drive cycle computation unit400computes a new value Tafter_cur for an after-adjustment drive cycle Tafter so as to satisfy the above first condition and second condition.

Then, in a step S104, the print controller302controls the head driver310so as to drive the piezoelectric elements121when the length of time corresponding to the after-adjustment drive cycle Tafter_cur has passed after the piezoelectric elements121is driven previously.

Then, the control shifts to a step S101. The destination of the control after the S104is not limited to the S101. After the step S104, the control may shift to the step S102or S103. For example, when the reading time interval is set to a pitch of 150 dots per inch (dpi) and the discharge interval of the ink droplets is set to 300 dpi, a pair of the steps S103and S104may be repeated twice and then the control may shift to the S101.

In the embodiment as described above with reference toFIG.12, the computation of the after-adjustment drive cycle is performed every time the value of the after-adjustment drive cycle is used one time. The computation of the after-adjustment drive cycle may be performed every time the value of the after-adjustment drive cycle is used two or more times. In other words, the computation of the after-adjustment drive cycle may be performed every time the after-adjustment drive cycles passes one or more times.

As described above, according to the present embodiment, the image forming apparatus that serves a liquid discharge apparatus includes the head driver310and the print controller302that serves as a discharge controller. The head driver310drives an actuator element such as the piezoelectric elements121that generate force to discharge an ink droplet from the head onto an object to be conveyed such as a sheet of paper that moves relative to the head. The print controller302computes a first drive cycle such as a before-adjustment drive cycle according to the amount of relative movement the object to be conveyed. Then, the print controller302adjusts the first drive cycle to a value within a second cycle range such as the cycle range503that is different from the first cycle range such as the cycle range501in which ink is abnormally discharged. As a result, a second drive cycle such as an after-adjustment drive cycle can be obtained. Then, the print controller302causes the head driver to drive the actuator elements in the second drive cycle. The print controller302executes processing for obtaining the second drive cycle every time the second drive cycles passes one or more times. Further, the print controller302adjusts the first drive cycle so that the difference between the accumulated value of the first drive cycle of a prescribed number of consecutive times such as n times and the accumulated value of the second drive cycle of a prescribed number of consecutive times such as n times does not exceed a permissible value such as Z.

Accordingly, the deterioration of the precision of discharging the ink droplet due to the resonance can be prevented.

More specifically, the print controller302adjusts the first drive cycle so as to satisfy the first condition and the second condition described above.

Accordingly, the landing position of the ink from can be prevented from being significantly displaced from the target position.

According to the present embodiment, a value obtained by dividing the distance determined according to the target resolution by the conveyance speed of the object to be conveyed can be set as a permissible value.

Accordingly, the influence of the displacement of the position at which ink is to be discharged from the target position on the image quality can be prevented.

According to the present embodiment, a value obtained by dividing a half value of the discharge position interval corresponding to the target resolution by the conveyance speed of the object to be conveyed can be set as a permissible value.

Accordingly, the influence of the displacement of the position at which ink is to be discharged from the target position on the image quality can be reduced to a level where such an influence cannot visually be recognized.

According to the present embodiment, a prescribed number of times is determined according to the target resolution.

Accordingly, the influence of the displacement of the position at which ink is to be discharged from the target position on the image quality can be reduced. According to the present embodiment, when the target resolution is “a” dpi, a value larger than the value obtained by the computation of 4×a/25.4 can be set as a prescribed number of times such as n times.

According to the present embodiment, the second cycle range includes a third cycle range such as the cycle range504that contacts the upper limit of the first cycle range and a fourth cycle range such as the cycle range505that contacts the lower limit of the first cycle range.

According to the present embodiment, the print controller302alternately adjusts the first drive cycle to the value within the third cycle range and the value within the fourth cycle range every time the after-adjustment drive cycle passes.

Accordingly, the amount of displacement of the position at which ink is to be discharged from the target position can be reduced compared with cases in which the first drive cycle is alternately adjusted to the value within the third cycle range and the value within the fourth cycle range every time the after-adjustment drive cycles passes two or more times.

According to the present embodiment, a method of discharging liquid includes a first step such as the steps S101and S102as illustrated inFIG.12of computing a first drive cycle according to the amount of relative movement of an object to be conveyed such as a sheet of paper moving relative to the head, a second step such as the repetition of the step S103inFIG.12of adjusting the first drive cycle to a value within a second cycle range different from the first cycle range in which ink droplets are abnormally discharged from the head to obtain a second drive cycle that is the adjusted first drive cycle as in, for example, the step S103inFIG.12every time the second drive cycles passes one or more times, and, and a third step such as the step S104inFIG.12of driving an actuator element that generates force to discharge an ink droplet from the head onto an object to be conveyed in the second driving cycle.

Accordingly, the deterioration of the precision of discharging the ink droplet due to the resonance can be prevented.

According to the present embodiment, the second step corresponds to a step of adjusting the first drive cycle so that the difference between the accumulated value of the first drive cycle of a prescribed number of consecutive times such as n times and the accumulated value of the second drive cycle of a prescribed number of consecutive times such as n times does not exceed a permissible value such as Z.

Accordingly, the amount of displacement of the position at which ink is to be discharged from the target position can be prevented from increasing due to accumulation.

In the above embodiment of the present disclosure, the liquid discharge apparatus is applied to an image forming apparatus of serial type in which the carriage23provided with the recording head in the direction orthogonal to the conveyance direction of a sheet of paper moves. However, no limitation is indicated thereby, and the liquid discharge device according to the above embodiments of the present disclosure may be applied to any kind of image forming apparatus.

For example, the liquid discharge apparatus according to the above embodiments of the present disclosure can also be applied to an image forming apparatus of line type in which the recording head relatively moves in the direction same as the conveyance direction of a sheet of paper to form an image. In such cases, an encoder that is arranged to detect the conveyance speed of a sheet of paper is read by a photosensor. Then, the first drive cycle is computed based on the read time interval by the photosensor, and the second drive cycle is computed in the same procedure as described above.

Moreover, even in a case where the liquid discharge apparatus according to the above embodiments of the present disclosure is applied to one of the serial-type image forming apparatus and the line-type image forming apparatus, the method of detecting the amount of relative movement of an object to be conveyed is not limited to the method of reading an encoder by a photosensor. The liquid discharge apparatus according to the above embodiments of the present disclosure can acquire the amount of relative movement of an object to be conveyed adopting any sort of method.

Moreover, the liquid discharge apparatus according to the above embodiments of the present disclosure can be applied to an any apparatus or device that discharges droplets of liquid from a nozzle to an object to be conveyed that moves relative to the nozzle.

Note that the liquid discharge device and the liquid discharging liquid according to the above embodiments of the present disclosure are preferred example embodiments of the present disclosure, and various applications and modifications may be made without departing from the scope of the invention. Further, any of the above-described multiple processes of the liquid discharging method according to the above embodiments of the present disclosure can be implemented as a hardware device such as a special-purpose circuit or device, software such as a program, or as a combination of both hardware and software such as a processor executing a software program.

Any one of the above-described multiple processes of the liquid discharging method according to the above embodiments of the present disclosure may be embodied in the form of a computer program stored in any kind of storage medium provided for a dedicated hardware. A sequence of operation is stored in such a storage medium, and is executed as instructed. Examples of such a storage medium include, but are not limited to, for example, a flexible disk, a hard disk, an optical disc, a magneto-optical disc, a magnetic tape, a nonvolatile memory card, and read-only-memory (ROM). Alternatively, any one of the above-described multiple processes of the liquid discharging method according to the above embodiments of the present disclosure may be implemented by one or more programmed general-purpose microprocessors capable of performing various kinds of operations or processes.

The program that includes a sequence of operation for the above-described multiple processes of the liquid discharging method according to the above embodiments of the present disclosure is a file in an installable or executable file format, and may be stored in a computer-readable recording medium such as a compact disk read-only memory (CD-ROM), a flexible disk (FD), a compact disk recordable (CD-R), and a digital versatile disk (DVD).

Moreover, the program that includes a sequence of operation for the above-described multiple processes of the liquid discharging method according to the above embodiments of the present disclosure may be stored in a computer connected to a network such as the Internet, and may be downloaded through the network. Further, a program that includes a sequence of operation for the above-described multiple processes of a liquid discharging method according to the above embodiments of the present disclosure may be distributed or downloaded through the network such as the Internet.