JP6379704B2 - Signal processing method - Google Patents

Description

  The present invention relates to a signal processing method for forming an image by droplet ejection.

  2. Description of the Related Art As an image forming apparatus such as a printer, a facsimile machine, a copying apparatus, and a multifunction machine of these, an apparatus using a liquid ejecting apparatus including a recording head composed of a liquid ejecting head that ejects ink droplets is known. The liquid ejecting apparatus is used to form an image by adhering ink to the sheet while conveying the sheet.

  In such an image forming apparatus, when ink is ejected by driving a piezoelectric element, there is a problem that the entire ink-jet head resonates, and so-called crosstalk occurs, resulting in an unstable ejection state. This is because the structural resonance frequency of the ink-jet head matches or is close to the drive frequency of the inkjet head, that is, the drive frequency of the piezoelectric element.

  With respect to the above problem, Patent Document 1 discloses a technique for preventing the drive frequency and fluid resonance frequency of the inkjet head from being included in the frequency range within the half-value width with respect to the structural resonance frequency of the inkjet head. Have been described.

  Patent Document 1 realizes that an inkjet drive frequency or the like is not included in a frequency range within a half-value width with respect to a structural resonance frequency by changing a pulse width itself with respect to a single striking drive waveform. doing.

  However, changing the pulse width itself means changing the frequency itself. For this reason, as in Patent Document 2, a drive waveform in an image forming apparatus that continuously ejects droplets of different sizes by selecting a plurality of drive pulses within one printing cycle and giving them to the droplet ejection head is shown in FIG. The above technique cannot be applied.

  The present invention has been made in view of such circumstances, and droplets having different sizes are ejected continuously by selecting a plurality of drive pulses within one printing cycle and applying them to the droplet ejection head. Even in such a case, an object of the present invention is to provide a signal processing method for preventing a driving frequency for discharging droplets from being included in a frequency region within a half width with respect to a structural resonance frequency.

In order to solve the above problems, the signal processing method of the present invention is a signal processing method related to processing of a drive signal given from a predetermined drive unit to a liquid discharge unit when a droplet is discharged from the predetermined liquid discharge unit. As a pre-process of generating a drive waveform including two or more drive signals within one drive cycle and a process of generating the drive waveform, the deformation amount of the nozzle surface is measured , resulting from the structure of the liquid ejecting means. Measuring the resonance frequency generated, determining whether the measured resonance frequency is a target frequency that affects the ejection of droplets by the liquid ejecting means, and measuring the resonance frequency is the target frequency. And a step of removing the frequency component of the resonance frequency determined to be the target frequency for each drive signal constituting the drive waveform.

  According to the present invention, even when a plurality of drive pulses are selected within one printing cycle and given to the droplet discharge head, droplets having different sizes are continuously discharged, so that the drive for discharging the droplets is performed. It is possible to prevent the frequency and the like from being included in the frequency region within the half width with respect to the structural resonance frequency.

1 is a schematic perspective view illustrating an example of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic configuration diagram illustrating a mechanism unit of an image forming apparatus according to an embodiment of the present invention. It is a principal part top view of the mechanism part in FIG. FIG. 3 is a cross-sectional view along the longitudinal direction of the liquid chamber showing an example of a liquid discharge head constituting the recording head of the image forming apparatus in the embodiment of the present invention. FIG. 5 is a cross-sectional view taken along the lateral direction of the liquid chamber of the liquid ejection head in FIG. 4. FIG. 2 is a schematic block diagram illustrating a control unit of the image forming apparatus according to the embodiment of the present invention. It is a block diagram which shows an example of the printing control part contained in the control part in FIG. FIG. 8 is a schematic diagram illustrating an example of a drive waveform generated and output by a drive waveform generation unit included in the print control unit in FIG. 7 and a droplet control signal for driving signal selection. It is a schematic diagram which shows the amount of ejection droplets corresponding to the droplet control signal in FIG. It is a schematic diagram which shows an example of the frequency characteristic of the structural vibration of a droplet discharge head. It is a schematic diagram showing an example of a drive waveform in a case where droplets having different sizes are continuously ejected by selecting a plurality of drive pulses within one printing cycle and giving them to the droplet ejection head. It is a schematic diagram which shows an example of the Fourier-transform result at the time of making the drive waveform in FIG. 11 discharge continuously. It is a schematic diagram which shows the signal processing process of the drive waveform regarding the drive waveform generation in embodiment of this invention. It is a schematic diagram which shows an example of the result of having removed the resonance frequency component from the waveform in FIG. It is a schematic diagram which shows an example of the drive waveform from which the resonant frequency component was removed as a result of the Fourier transform. It is a flowchart explaining the signal processing process in embodiment of this invention.

  An image forming apparatus to which a signal processing method according to an embodiment of the present invention is applied will be described below with reference to the drawings. However, the present invention is not limited to this embodiment unless it exceeds the gist of the present invention. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified thru | or abbreviate | omitted suitably.

  An example of an image forming apparatus according to the present embodiment will be described with reference to FIG. An image forming apparatus according to the present embodiment includes a main body 1, a paper feed tray 2 for loading paper loaded in the main body 1, and a paper discharge tray 3 for stocking paper on which an image is formed that is detachably attached to the main body 1. Is provided.

  Further, a cartridge loading portion 4 for loading an ink cartridge that protrudes from the front surface to the front side of the main body 1 and is lower than the upper surface is formed on one end portion side of the front surface of the main body 1, that is, on the side of the paper supply / discharge tray. Have. Further, the upper surface of the cartridge loading unit 4 is provided with an operation / display unit 5 provided with operation buttons, a display, and the like.

  The cartridge loading unit 4 includes, for example, ink cartridges 10k, 10c, 10m, and 10y containing black (K) ink, cyan (C) ink, magenta (M) ink, and yellow (Y) ink, respectively. It can be loaded by inserting from the front side toward the rear side. A cartridge cover 6 that is a front cover that is opened when the ink cartridge 10 is attached or detached is provided on the front side of the cartridge loading unit 4 so as to be openable and closable.

  Further, the operation / display unit 5 displays a remaining amount display unit for each color for displaying that the remaining amount of the ink cartridge for each color has reached the near end at the position corresponding to the mounting position of the ink cartridge for each color. 11k, 11c, 11m, and 11y are arranged. Further, the operation / display unit 5 includes a power button 12, a paper feed / print restart button 13, and a cancel button 14.

  Next, the mechanism of the image forming apparatus according to the present embodiment will be described with reference to FIGS. In this embodiment, the carriage 23 is slidably held in the main scanning direction by a guide rod 21 and a stay 22 which are guide members laid horizontally between left and right side plates (not shown). The carriage 23 is moved and scanned in the direction of the arrow by a main scanning motor 24 via a timing belt 27 spanned between a driving pulley 25 and a driven pulley 26.

  In the carriage 23, recording heads 31k, 31c, 31m, and 31y as liquid ejecting means for ejecting the ink droplets of the respective colors described above are arranged in a direction crossing the main scanning direction to eject ink droplets. It is mounted with the direction facing downward.

  As an ink jet head, a piezoelectric actuator such as a piezoelectric element, or a thermal actuator that uses a phase change caused by film boiling of a liquid using an electrothermal transducer such as a heating resistor, a pressure that generates pressure for ejecting droplets. Those provided as generating means can be used. In addition to the above, it is possible to use a shape memory alloy actuator using a metal phase change due to a temperature change, an electrostatic actuator using an electrostatic force, and the like as pressure generating means.

  Note that the inkjet head has a configuration in which a plurality of nozzle rows are arranged and a plurality of nozzle rows are arranged and droplets of the same color are ejected from each nozzle row. Also good. The carriage 23 is mounted with a head tank 32 of each color for supplying ink of each color to the recording head 31.

  The head tank 32 is replenished and supplied with ink of each color from the ink cartridge 10 of each color mounted in the cartridge loading unit 4 via the ink supply tube of each color. On the other hand, a sheet feeding roller 43 and a separation pad 44 are provided as a sheet feeding unit which is a feeding unit for feeding the sheets 42 stacked on the sheet stacking unit 41 of the sheet feeding tray 2. The paper feed roller 43 separates and feeds the papers 42 from the paper stacking unit 41 one by one. The separation pad 44 is made of a material having a large friction coefficient, faces the paper feed roller 43 and is urged toward the paper feed roller 43 side.

  The image forming apparatus according to the present exemplary embodiment includes a guide member 45 that guides the paper 42, a counter roller 46, a conveyance guide member 47, and a pressing member 48 having a tip pressure roller 49. With these configurations, the sheet 42 fed from the sheet feeding unit is sent to the lower side of the recording head 31. Further, the image forming apparatus according to the present embodiment includes a conveyance belt 51 that is a conveyance unit for electrostatically attracting the fed paper 42 and conveying it at a position facing the recording head 31.

  The conveyance belt 51 is an endless belt, and is configured to be looped around the conveyance roller 52 and the tension roller 53 and to circulate in the belt conveyance direction, that is, the sub-scanning direction. The conveyor belt 51 has a surface layer that serves as a sheet adsorption surface and a back layer that is made of the same material as the surface layer and is subjected to resistance control by carbon. The surface layer is formed of, for example, a pure resin material having a thickness of about 40 μm which is not subjected to resistance control, for example, ETFE pure material, and the back layer is, for example, a medium resistance layer or an earth layer.

  The image forming apparatus according to the present exemplary embodiment includes a charging roller 56 that is a charging unit for charging the surface of the conveyance belt 51. The charging roller 56 is disposed so as to contact the surface layer of the conveyor belt 51 and rotate following the rotation of the conveyor belt 51, and applies a predetermined pressing force to both ends of the shaft as a pressing force.

  The transport roller 52 also functions as an earth roller, and is in contact with the middle resistance layer of the transport belt 51 and is grounded. In addition, a guide member 57 is disposed on the back side of the conveyance belt 51 so as to correspond to a printing area by the recording head 31.

  The guide member 57 protrudes toward the recording head 35 with respect to the tangent line between the conveying roller 52 and the tension roller 53 that are two rollers whose upper surfaces support the conveying belt 51. Thereby, the highly accurate flatness of the conveyor belt 51 is maintained. The conveyance belt 51 rotates in the belt conveyance direction of FIG. 3, that is, the sub-scanning direction when the conveyance roller 52 is rotationally driven by the sub-scanning motor 58 via the drive belt 59 and the pulley 60.

  Further, as a paper discharge unit for discharging the paper 42 recorded by the recording head 31, a separation claw 61 for separating the paper 42 from the conveyance belt 51, a paper discharge roller 62, and a paper discharge roller 63 are provided. The paper discharge tray 3 is provided below the paper discharge roller 62.

  A duplex unit 71 is detachably mounted on the back surface of the apparatus body 1. The duplex unit 71 takes in the paper 42 returned by the reverse rotation of the transport belt 51, reverses it, and feeds it again between the counter roller 46 and the transport belt 51. The upper surface of the duplex unit 71 is a manual feed tray 72.

  Further, as shown in FIG. 3, a maintenance / recovery mechanism 81 including a recovery means for maintaining and recovering the nozzle state of the recording head 31 is arranged in the non-printing area on one side of the carriage 23 in the scanning direction. Yes. The maintenance / recovery mechanism 81 includes cap members 82a to 82d (hereinafter referred to as “caps”), a wiper blade 83, an idle discharge receiver 84, and the like.

  The cap caps each nozzle surface of the recording head 31. The wiper blade 83 is a blade member for wiping the nozzle surface. The idle ejection receiver 84 receives droplets when performing idle ejection for ejecting droplets that do not contribute to recording in order to discharge the thickened recording liquid. Here, the cap 82a is a sucking and moisturizing cap (hereinafter referred to as "suction cap"), and the other caps 82b to 82d are moisturizing caps.

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

  In the ink jet recording apparatus configured as described above, the sheets 42 are separated and fed one by one from the sheet feeding tray 2, and the sheet 42 fed substantially vertically upward is guided by the guide member 45. The sheet 42 is conveyed while being sandwiched between the conveyance belt 51 and the counter roller 46, and further guided by the conveyance guide 37 and pressed against the conveyance belt 51 by the tip pressure roller 49, and is conveyed by approximately 90 °. Changed direction.

  At this time, a positive voltage and a negative voltage are alternately applied to the charging roller 56 from the AC bias supply unit by a control unit (not shown), that is, an alternating voltage is applied. As a result, the charging voltage pattern in which the conveyor belt 51 alternates, that is, plus and minus are alternately charged in a band shape with a predetermined width in the sub-scanning direction that is the circumferential direction.

  When the paper 42 is fed onto the conveyance belt 51 that is alternately charged with plus and minus, the paper 42 is attracted to the conveyance belt 51, and the paper 42 is conveyed in the sub-scanning direction by the circular movement of the conveyance belt 51. Therefore, the recording head 31 is driven according to the image signal while moving the carriage 23. Thus, ink droplets are ejected onto the stopped paper 42 to record one line, and after the paper 42 is conveyed by a predetermined amount, the next line is recorded.

  Upon receiving a recording end signal or a signal that the trailing edge of the paper 42 has reached the recording area, the recording operation is finished and the paper 42 is discharged onto the paper discharge tray 3. Further, during printing standby, the carriage 23 is moved to the maintenance / recovery mechanism 81 side, and the recording head 31 is capped by the cap 82 to keep the nozzles moist, thereby preventing ejection failure due to ink drying.

  Further, in a state where the recording head 31 is capped with the cap 82, a recovery operation is performed in which the recording liquid is sucked from the nozzle by a suction pump (not shown) and the thickened recording liquid and bubbles are discharged. Further, before the start of recording, during recording, etc., an empty ejection operation for ejecting ink not related to recording toward the idle ejection receptacles 84 and 88 is performed. That is, droplets that do not contribute to image formation are ejected. As a result, the stable ejection performance of the recording head 31 is maintained and recovered.

  Next, an example of the liquid discharge head in the image forming apparatus of this embodiment will be described with reference to FIGS. In this liquid discharge head, a flow path plate 101, a vibration plate 102, and a nozzle plate 103 are joined and laminated, and a nozzle communication path 105, which is a flow path through which a nozzle 104 that discharges droplets communicates, and liquid An ink supply port 109 communicating with a common liquid chamber 108 for supplying ink to the chamber 106 and the liquid chamber 106 is formed.

  The channel plate 101 is formed by etching a SUS substrate or a single crystal silicon substrate, for example. The diaphragm 102 is formed by, for example, nickel electroforming bonded to the lower surface of the flow path plate 101. The nozzle plate 103 is joined to the upper surface of the flow path plate 101.

  In addition, as a pressure generating means for pressurizing the ink in the liquid chamber 106 by deforming the vibration plate 102, that is, an electromechanical conversion element as an actuator means, two rows of stacked piezoelectric elements 121 and the piezoelectric elements 121 are arranged. And a base substrate 122 to be bonded and fixed. Note that a column portion 123 is provided between the piezoelectric elements 121. The column portion 123 is a portion formed simultaneously with the piezoelectric element 121 by dividing and processing the piezoelectric element member. However, since the drive voltage is not applied, the column portion 123 is simply a column.

  Further, an FPC cable 126 is connected to the piezoelectric element 121 for connection to a drive IC which is a drive circuit (not shown). Then, the peripheral edge of the diaphragm 102 is joined to the frame member 130.

  The frame member 130 is formed with a through portion 131 and an ink supply hole 132. The through portion 131 houses an actuator unit composed of the piezoelectric element 121, the base substrate 122, and the like. The ink supply hole 132 is a recess that becomes the common liquid chamber 108, and supplies ink to the common liquid chamber 108 from the outside. The frame member 130 is formed by injection molding with a thermosetting resin such as an epoxy resin or polyphenylene sulfite, for example.

  Here, the flow path plate 101 is anisotropically etched using, for example, an alkaline etching solution such as a potassium hydroxide aqueous solution (KOH) on a single crystal silicon substrate having a crystal plane orientation [110]. By this, or by etching the SUS substrate, the recesses and the holes that become the nozzle communication path 105 and the liquid chamber 106 are formed.

  The vibration plate 102 is formed from a nickel metal plate, and is manufactured by, for example, an electroforming method (electroforming method). Alternatively, a metal plate or a joining member between a metal and a resin plate may be used. it can. The piezoelectric element 121 and the column part 123 are bonded to the diaphragm 102 with an adhesive, and the frame member 130 is further bonded with an adhesive.

  The nozzle plate 103 forms a nozzle 104 having a diameter of 10 to 30 μm corresponding to each liquid chamber 106 and is bonded to the flow path plate 101 with an adhesive. The nozzle plate 103 is obtained by forming a water repellent layer on the outermost surface of a nozzle forming member made of a metal member via a required layer. The surface of the nozzle plate 103 becomes the nozzle surface 31a.

  The piezoelectric element 121 is a stacked piezoelectric element in which piezoelectric materials 151 and internal electrodes 152 are alternately stacked. An individual electrode 153 and a common electrode 154 are connected to each internal electrode 152 drawn to alternately different end faces of the piezoelectric element 121.

  In this embodiment, the ink in the liquid chamber 106 is pressurized using the displacement in the d33 direction as the piezoelectric direction of the piezoelectric element 121. However, the pressure in the d31 direction is used as the piezoelectric direction of the piezoelectric element 121. The ink in the liquid chamber 106 may be pressurized. Alternatively, a structure in which one row of piezoelectric elements 121 is provided on one substrate 122 may be employed.

  In the liquid ejection head configured as described above, for example, by lowering the voltage applied to the piezoelectric element 121 from the reference potential, the piezoelectric element 121 contracts, and the vibration plate 102 descends to expand the volume of the liquid chamber 106. As a result, ink flows into the liquid chamber 106.

  Thereafter, the voltage applied to the piezoelectric element 121 is increased to extend the piezoelectric element 121 in the stacking direction, and the diaphragm 102 is deformed in the nozzle 104 direction to contract the volume / volume of the liquid chamber 106. As a result, the recording liquid in the liquid chamber 106 is pressurized, and droplets of the recording liquid are ejected from the nozzle 104.

  Then, by returning the voltage applied to the piezoelectric element 121 to the reference potential, the diaphragm 102 is restored to the initial position, and the liquid chamber 106 expands to generate a negative pressure. Therefore, at this time, the recording liquid is filled into the liquid chamber 106 from the common liquid chamber 108. Therefore, after the vibration of the meniscus surface of the nozzle 104 is attenuated and stabilized, the operation proceeds to the next droplet discharge.

  Note that the driving method of the head is not limited to the above-described example of pulling / pushing, and it is also possible to perform striking or pushing depending on the direction to which the drive waveform is given.

  Next, an overview of the control unit of the image forming apparatus in the present embodiment will be described with reference to FIG. The control unit includes a main control unit 301 and a print control unit 302. The main control unit 301 is composed of a microcomputer that also serves as a means for controlling the idle ejection operation according to the present invention, which controls the entire image forming apparatus. The print control unit 302 is configured by a microcomputer that controls printing.

  Then, the main control unit 301 performs the following control to form an image on the paper 42 based on the print processing information input from the communication circuit 300. The control includes driving control of the main scanning motor 24 and sub-scanning motor 58 via the main scanning motor driving circuit 303 and sub-scanning motor driving circuit 304, and control of sending print data to the print control unit 302. .

  Further, the main control unit 301 receives a detection signal from a carriage position detection circuit 305 that detects the position of the carriage 23. The main control unit 301 controls the movement position and movement speed of the carriage 23 based on this detection signal.

  The carriage position detection circuit 305 detects the position of the carriage 23 by, for example, reading and counting the number of slits of an encoder sheet arranged in the scanning direction of the carriage 23 with a photosensor mounted on the carriage 23.

  The main scanning motor drive circuit 303 rotates the main scanning motor 24 according to the carriage movement amount input from the main control unit 301 to move the carriage 23 to a predetermined position at a predetermined speed.

  Further, the main control unit 301 receives a detection signal from a conveyance amount detection circuit 306 that detects the movement amount of the conveyance belt 51. The main control unit 301 controls the moving amount and moving speed of the conveyor belt 51 based on this detection signal.

  The conveyance amount detection circuit 306 detects the conveyance amount by, for example, reading and counting the number of slits of the rotary encoder sheet attached to the rotation shaft of the conveyance roller 52 with a photo sensor.

  The sub-scanning motor driving circuit 304 rotates the sub-scanning motor 58 in accordance with the conveyance amount input from the main control unit 301 to rotate the conveyance roller 52 to move the conveyance belt 51 to a predetermined position at a predetermined speed. Move with.

  The main control unit 301 rotates the sheet feeding roller 43 once by giving a sheet feeding roller driving command to the sheet feeding roller driving circuit 307. Further, the main control unit 301 rotationally drives the motor 221 of the maintenance / recovery mechanism 81 via the maintenance / recovery mechanism drive motor drive circuit 308. As a result, the cap 82 is moved up and down, the wiper blade 83 is moved up and down, and the suction pump is driven as described above.

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

  Further, the main control unit 301 takes in information stored in the cartridge EEPROM 316 provided in each ink cartridge 10 attached to the cartridge loading unit 4 through the cartridge communication circuit 314. For example, the main control unit 301 performs a required process, and stores and holds the acquired information in the EEPROM 315.

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

  The print control unit 302 generates pressure for discharging droplets of the recording head 31 based on the signal from the main control unit 301 and the carriage position and conveyance amount from the carriage position detection circuit 305 and the conveyance amount detection circuit 306. Data for driving the means is generated. The print control unit 302 transfers this data to the head drive circuit 310 as serial data, and transfers a transfer clock, a latch signal, a mask signal as a droplet control signal, and the like necessary for the transfer of the data and confirmation of the transfer. It outputs to 310.

  Further, the print control unit 302 gives the drive waveform pattern data and the head driver composed of a D / A converter, a voltage amplifier, a current amplifier, and the like that perform D / A conversion on the drive signal pattern data stored in the ROM. Drive waveform selection means is included. The print control unit 302 generates a drive waveform including a plurality of drive signal groups including one drive pulse or a plurality of drive pulses, which are drive signals, and outputs the drive waveform to the head drive circuit 310.

  The head drive circuit 310 is a drive unit that gives a drive signal to the recording head 31. Specifically, the head driving circuit 310 drives the recording head 31 by selectively applying a driving signal to the driving element of the recording head 31 based on predetermined image data.

  The predetermined image data is, for example, image data corresponding to one line of the recording head 31 input serially. Further, the drive signal constitutes a drive waveform given from the print control unit 302. The drive element is, for example, a piezoelectric element as described above that generates energy for discharging droplets, which is provided in the recording head 31.

  At this time, by selecting a drive pulse of a drive signal group that constitutes a drive waveform, it is possible to eject droplets having different sizes and to sort dots having different sizes.

  Next, an example of the print control unit 302 and the head drive circuit 310 will be described with reference to FIG. The print control unit 302 includes a drive waveform generation unit 401 and a data transfer unit 402. The drive waveform generation unit 401 generates and outputs a drive waveform, that is, a common drive waveform. The data transfer unit 402 outputs 2-bit image data [gradation signals 0, 1] corresponding to the print image, a clock signal, a latch signal, and droplet control signals MN0 to MN3.

  The drive waveform generation unit 401 is a drive waveform generation unit that generates a drive waveform including two or more drive signals within one drive cycle. Specifically, as illustrated in FIG. 8A described later, the drive waveform generation unit 401 includes a first drive signal group PG1 including one or a plurality of drive signals in one drive cycle, and 1 Alternatively, a drive waveform continuously including the second drive signal group PG2 composed of a plurality of drive signals is generated and output. In the present embodiment, two drive signal groups will be described as an example, but a configuration in which three or more drive signal groups are generated and output may be used.

  In addition, the data transfer unit 402 uses the first drive signal group PG1 and the second drive signal group PG2 as droplet control signals MN0 to MN3 for selecting a drive signal from the first drive signal group PG1 and the second drive waveform group PG2. Is output continuously within one drive cycle in accordance with the output of.

  The droplet control signals MN0 to MN3 are 2-bit signals that instruct the opening and closing of the analog switch 415 that is the switch means of the head driving circuit 310 for each droplet. Further, the droplet control signals MN0 to MN3 make a state transition to the L level with waveforms to be selected in accordance with the cycles of the first drive waveform group PG1 and the second drive waveform group PG2, and make a state transition to the H level when not selected.

  The head drive circuit 310 includes a shift register 411, a latch circuit 412, a decoder 413, a level shifter 414, and an analog switch 415.

  The shift register 411 receives a shift clock that is a transfer clock from the data transfer unit 402 and gradation data [2 bits / CH] that is serial image data. The latch circuit 412 latches each resist value of the shift register 411 with a latch signal. The decoder 413 decodes the gradation data and the first and second drop control signals MN0a to MN3a and MN0b to MN3b and outputs the result.

  The level shifter 414 converts the logic level voltage signal of the decoder 413 to a level at which the analog switch 415 can operate. The analog switch 415 is turned on / off by the output of the decoder 413 given through the level shifter 414. The analog switch 415 is connected to the individual electrode 154 that is a selection electrode of each piezoelectric element 121, and the common drive waveform from the drive waveform generation unit 401 is input thereto.

  The analog switch 415 is turned on according to the result of decoding the serially transferred image data and the droplet control signals MN0 to MN3 by the decoder 413. As a result, the required drive signals constituting the first drive signal group PG1 and the second drive signal group PG2 included in the common drive waveform pass, that is, are selected and applied to the piezoelectric element 121.

  An example of the drive waveform output from the drive waveform generation unit 401 and the droplet control signal output from the data transfer unit 402 will be described with reference to FIGS. As shown in FIG. 8A, the first drive waveform group PG1 output from the drive waveform generation unit 401 includes a non-ejection drive pulse P1 and ejection drive pulses P2 and P3.

  The non-ejection drive pulse P1 includes a waveform element that falls from the reference potential Ve, a waveform element that is held at the potential after the fall, and a waveform element that rises as it is to the reference potential Ve after the hold. The ejection drive pulses P2 and P3 are composed of a waveform element that falls from the reference potential Ve, a waveform element that is held at the potential after the fall, and a waveform element that rises stepwise up to the reference potential Ve after the hold.

  Note that the non-ejection driving pulse means a driving pulse that drives the piezoelectric element 121 but does not eject droplets from the nozzle only by vibrating the meniscus. The ejection driving pulse means a driving pulse for driving the piezoelectric element 121 and ejecting a droplet from the nozzle.

  The second drive waveform group PG2 generated and output in succession to the first drive waveform group PG1 is composed of the ejection drive pulse P4 and the ejection drive pulse P5. The ejection drive pulse P4 includes a waveform element that falls from the reference potential Ve, a waveform element that is held at the potential after the fall, and a waveform element that rises as it is to the reference potential Ve after the hold.

  The ejection drive pulse P5 is held at the waveform element that falls from the reference potential Ve, the waveform element that is held at the potential after the fall, the waveform element that rises as it is to a potential higher than the reference potential Ve after the hold, and the potential after the rise. The driving pulse P5 includes a waveform element and a waveform element that falls to the reference potential Ve after being held.

  Here, the waveform element in which the potential V of the drive pulse falls from the reference potential Ve is a drawing waveform element in which the piezoelectric element 121 contracts and the volume of the pressurized liquid chamber 106 expands. Further, the waveform element that rises from the state after the fall is a pressurizing waveform element that causes the piezoelectric element 121 to expand and the volume of the pressurized liquid chamber 106 to contract.

  For this drive waveform, the data transfer unit 402, as shown in FIG. 8B, the drive pulses P1 to P3 constituting the first drive waveform group PG1 and the drive pulses P4 and P5 constituting the second drive waveform group PG2. The droplet control signals MN0 to MN3 for selecting are sequentially output.

  In the droplet control signals MN0 to MN3, as shown in FIG. 9, by supplying the droplet control signal MN0, only the driving pulse P1 is selected and applied to the head. As a result, the non-ejection driving state is set, that is, the ejection droplet amount is 0 pl.

  Similarly, by supplying the droplet control signal MN1, only the driving pulse P3 is selected and applied to the head, so the ejection droplet amount is 3 pl. Further, since the drive pulses P2 and P4 are selected and given to the head by giving the droplet control signal MN2, the ejection droplet amount becomes 9 pl. Furthermore, since the driving pulses P2 to P5 are selected and given to the head by giving the droplet control signal MN3, the ejection droplet amount becomes 18 pl.

  That is, by selecting the drive pulses P1 to P5 constituting the drive waveform by the four 2-bit droplet control signals MN0 to MN3, non-ejection [0pl], small droplet [3pl], medium droplet [9pl], Four types of large droplets [18 pl] can be obtained. That is, according to the present embodiment, droplets having different sizes can be ejected with a simple configuration.

  Next, the frequency characteristics of the structural vibration of the recording head will be described with reference to FIG. In this figure, the vertical axis indicates the speed when the amount of deformation of the head nozzle surface measured by a laser Doppler meter when driving one pressure chamber by sine wave input, and the horizontal axis indicates the driving frequency. The numerical value on the vertical axis corresponds to the deformation amount of the head, and the larger the numerical value, the larger the deformation amount of the head.

  As is clear from FIG. 10, in this head, a large resonance can be confirmed at 395 kHz. Although other resonances can be seen, since it does not have a peak of about 395 kHz, 395 kHz may be considered as a representative here. If the peak value of the resonance spectrum frequency coincides with or is close to the driving frequency of the ink jet head, the structural resonance of the recording head is excited and the ejection stability is adversely affected.

  Next, an example of a drive waveform in a case where droplets of different sizes are continuously ejected by selecting a plurality of drive pulses within one printing cycle and giving them to the droplet ejection head will be described with reference to FIG. . As shown in this figure, because the drive waveform is composed of multiple pulses, if the pulse width itself is changed for a single strike drive waveform, the waveform itself will be different, and the desired droplet will be Cannot be discharged.

  Next, a Fourier transform result when the drive waveform shown in FIG. 11 is continuously discharged will be described with reference to FIG. In the case of this waveform, it can be seen that it has a frequency component at 395 kHz as indicated by the arrow. Although there are other input frequency components, it appears in the amplitude as vibration due to the characteristics of the input x transmission system, that is, the multiplication of FIG. 12 and FIG. Therefore, it is clear that even if a frequency other than 395 kHz can be confirmed as an input signal, there is no need to consider it because it does not have resonance of the transmission system or is a small frequency band.

  In the present embodiment, the above-described 395 kHz component is removed from the input waveform. This is because by removing the 395 kHz component from the input waveform, an effect that does not appear as vibration is obtained even if there is resonance.

  Therefore, in the image forming apparatus according to the present embodiment, as shown in FIG. 13, as a pre-process for inputting a drive waveform to the drive waveform generation unit, a drive waveform generation process 450, a resonance frequency measurement process 451, and a target frequency determination process 452. Then, signal processing is performed in the order of the filter step 453. The filter process 453 includes a Fourier transform process 454 and an inverse Fourier transform process 455.

  In the resonance frequency measurement step 451, the resonance frequency generated due to the structure of the droplet discharge means such as the recording head 31, for example, is measured. In a target frequency determination step 452, it is determined whether or not the resonance frequency measured in the resonance frequency measurement step 451 is a target frequency that affects the ejection of droplets by the recording head 31.

  In the filter step 453, when the resonance frequency measured in the resonance frequency measurement step 451 is determined as the target frequency in the target frequency determination step 452, the frequency component of the resonance frequency determined as the target frequency is driven. It is removed for each drive signal constituting the waveform.

  Further, in the filter step 453, the frequency component of the resonance frequency is revealed by the Fourier transform of the drive waveform in the Fourier transform step 454. In the filter step 453, a frequency characteristic obtained by removing the revealed frequency component is generated, and the frequency component removal drive waveform obtained by performing the inverse Fourier transform on the generated frequency characteristic in the inverse Fourier transform step 455 is next applied. In step 456, the signal is input to the drive waveform generator 401.

  As a specific example, a target for removing 395 kHz fluctuation is first determined, and the frequency component of 395 kHz in FIG. 12 is removed as indicated by a broken line in FIG. As the phase information, the same information as the result of Fourier transform of the waveform of FIG. 11 is used. Next, based on the amplitude in FIG. 14 and phase information obtained by Fourier transform of FIG. 11, inverse Fourier transform is performed to obtain a drive waveform from which a 395 kHz component has been removed.

  FIG. 15 shows the result of Fourier analysis. In FIG. 14, the broken line is a waveform obtained by removing the frequency component of 395 kHz. Note that the drive waveform before the frequency component removal shown in FIG. 11 is shown by a solid line.

  As described above, since the drive waveform from which the resonance frequency component due to the structure of the apparatus is removed can be generated, this waveform is input to the drive waveform generation unit 401. As a result, the following effects can also be obtained in an image forming apparatus that continuously ejects droplets of different sizes by selecting a plurality of drive pulses within one printing cycle and applying them to the droplet ejection head.

  That is, according to this embodiment, the drive frequency of the inkjet head is prevented from being included in the frequency region within the half-value width with respect to the structural resonance frequency of the recording head, and crosstalk occurs and an unstable ejection state occurs. Can be avoided.

  Next, the signal processing process of the drive waveform related to the above-described resonance frequency removal in the present embodiment will be described with reference to FIG.

  First, in the drive waveform generation step 450, the drive waveform generation unit 401 designs a drive waveform without particularly considering the resonance frequency component (step S1). Next, in the resonance frequency measurement step 451, for example, the mechanical resonance frequency of the head drive circuit 310, which is a drive means, is measured (step S2).

  Next, in a target frequency determination step 452, a target frequency that affects ejection is determined from among the frequencies that appear from the result (step S3). When the target frequency is not determined (step S4, NO), the designed drive waveform is input to the drive waveform generation unit 401 as it is (step S8).

  On the other hand, when the target frequency is determined in 1504 (step S4, YES), in the filter step 453, the designed drive waveform is Fourier-transformed (step S5), and a frequency characteristic in which the target frequency is deleted is generated (step S6). ). In the filter step 453, the obtained frequency characteristic is subjected to inverse Fourier transform (step S7), and the obtained drive waveform is input to the drive waveform generating unit 401 (step S8).

  As described above, according to the present embodiment, since the frequency at the peak can be pinpointed, the frequency characteristics can be improved even when the structural resonance frequency is large or close. .

  Further, it goes without saying that the Fourier transform in the present embodiment may include, for example, a fast Fourier transform (FFT) or a discrete Fourier transform (DCT: Discrete Fourier Transform).

  The above-described embodiment is a preferred embodiment of the present invention, and various modifications can be made without departing from the gist of the present invention. For example, each process in the image forming apparatus of the present embodiment described above can be executed using hardware, software, or a combined configuration of both.

  In the case of executing processing using software, it is possible to install and execute a program in which a processing sequence is recorded in a memory in a computer incorporated in dedicated hardware. Alternatively, the program can be installed and executed on a general-purpose computer capable of executing various processes.

401 Drive waveform generation unit 451 Resonance frequency measurement process 452 Target frequency determination process 453 Filter process 454 Fourier transform process 455 Inverse Fourier transform process

Japanese Patent No. 4815364

Claims (4)

A signal processing method related to processing of a driving signal given from a predetermined driving unit to the liquid discharging unit when discharging a droplet from the predetermined liquid discharging unit,
Generating a drive waveform including two or more of the drive signals within one drive cycle;
As a pre-process of the step of generating the drive waveform,
Measuring a deformation amount of the nozzle surface, and measuring a resonance frequency generated due to the structure of the liquid ejection means;
Determining whether the measured resonance frequency is a target frequency that affects the ejection of droplets by the liquid ejection means;
Removing the frequency component of the resonance frequency determined to be the target frequency for each of the drive signals constituting the drive waveform when it is determined that the measured resonance frequency is the target frequency;
A signal processing method comprising:   The signal processing method according to claim 1, wherein a frequency component of the resonance frequency is revealed by Fourier transform on the driving waveform.   3. The signal processing method according to claim 2, wherein a frequency characteristic is generated by removing the revealed frequency component, and a frequency component removal drive waveform is generated by performing inverse Fourier transform on the generated frequency characteristic. Two or more of the drive signals included in the drive waveform generated by removing the frequency component of the resonance frequency determined to be the target frequency for each of the drive signals constituting the drive waveform are selected. And commonly used for drops of different sizes
  The signal processing method as described in any one of Claims 1 thru | or 3.

Images