JP2017109480A - Image forming device, image forming method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress occurrence of white streaks and improve image quality.SOLUTION: The image forming device, which includes at least a first recording head and a second recording head, comprises: sensing means that senses defective nozzles in the first recording head and in the second recording head; and control means that controls amounts of liquid droplets discharged from a nozzle adjacent to the defective nozzle in the first recording head and amounts of liquid droplets discharged from a nozzle adjacent to the defective nozzle in the second recording head when an impact position of the liquid droplets from the defective nozzle in the first recording head and an impact position of the liquid droplets from the defective nozzle in the second recording head are the same.SELECTED DRAWING: Figure 16

Description

  The present invention relates to an image forming apparatus, an image forming method, and a program.

  In recent years, inkjet line printers capable of high-speed printing have been released by various companies in order to improve productivity. In addition, the demand for higher image quality has been increasing year by year, and types of printers with improved recording density have appeared.

  Due to these measures, the use of inkjet printers in the market is increasing. As a result, it has been increasingly used for various purposes, and various types of recording media have been used.

  Printing has become common from monochrome to color, and various types have been developed, from four color types of CMYK (cyan, magenta, yellow, black) to those with additional green, orange, and light inks (for example, (See Patent Documents 1 and 2.)

  The invention described in Patent Document 1 relates to a printer, a printer driving method, and a recording medium on which the printer driving method is recorded. In particular, when applied to a multi-head line printer, some nozzles constituting the multi-head have failed. In this case, it is an object to prevent a significant deterioration in the quality of the printing result. Specifically, the drive is switched so as to increase the dot diameter of the nozzle adjacent to the failed nozzle due to the failure of the nozzle.

In an ink jet recording apparatus, a technique is known in which when an ejection failure ink nozzle is detected, the amount of droplets from an adjacent nozzle is increased to suppress the occurrence of white stripes.
However, even when ejection failure occurs at the same location in different heads, the amount of liquid droplets is increased in the same manner, causing a problem that ink overflow occurs and image quality deteriorates.

  Therefore, an object of the present invention is to suppress the occurrence of white stripes and aim to improve image quality.

  In order to solve the above-described problem, the invention described in claim 1 is an image forming apparatus including at least a first recording head and a second recording head, wherein the first recording head and the second recording head are included. The detecting means for detecting the defective nozzle in the head, the landing position of the droplet from the defective nozzle of the first recording head, and the landing position of the droplet from the defective nozzle of the second recording head are the same. In this case, the control for controlling the droplet amount discharged from the nozzle adjacent to the defective nozzle of the first recording head and the droplet amount discharged from the nozzle adjacent to the defective nozzle of the second recording head. And means.

  According to the present invention, it is possible to suppress the occurrence of white stripes and improve image quality.

1 is an explanatory side view illustrating an overall configuration of a mechanism unit of an image forming apparatus according to an embodiment. FIG. 2 is an explanatory plan view of a mechanism unit of the image forming apparatus illustrated in FIG. 1. FIG. 3 is a conceptual diagram of a line-type printer including heads that include a sheet width and each color. FIG. 2 is a cross-sectional explanatory view along the longitudinal direction of the liquid chamber of the recording head of the image forming apparatus shown in FIG. 1. FIG. 2 is an explanatory cross-sectional view of the recording head of the image forming apparatus illustrated in FIG. 1 in the liquid chamber short direction (nozzle arrangement direction). FIG. 2 is an example of a functional block diagram of the image forming apparatus illustrated in FIG. 1. 2 is a block diagram illustrating a hardware configuration example of an image forming apparatus 600 of the present embodiment. FIG. 3 is a block diagram illustrating a configuration example of a recording head control unit 910, a drive waveform generation circuit 707, and a recording head driver 210. FIG. FIG. 2 is an explanatory diagram illustrating an example of a drive waveform generated and output by a drive waveform generation unit of a printing control unit of the image forming apparatus illustrated in FIG. 1. (A) is explanatory drawing for demonstrating the small droplet selected from a drive waveform, (b) is explanatory drawing for demonstrating the medium droplet selected from a drive waveform. (C) is explanatory drawing for demonstrating the large droplet selected from a drive waveform, (d) is explanatory drawing for demonstrating the fine drive selected from a drive waveform. It is explanatory drawing for demonstrating the drive waveform according to the viscosity of an ink. It is a block diagram which shows the structural example of the image process part 810 shown in FIG. 1 is a block diagram illustrating an example of an image forming system according to the present invention. 1 is a block diagram illustrating an example of an image processing apparatus in an image forming system according to the present invention. It is an example of the flowchart of a nozzle missing detection. It is an example of a flowchart of nozzle omission correction. (A) is a schematic head diagram, (b) is a schematic dot diagram without nozzle omission correction, and (c) is a schematic dot diagram during adjacent dot size modulation. (A) is a schematic diagram of a cyan head, (b) is a schematic diagram of a magenta head, and (c) is a schematic diagram of dots at the time of dot size modulation from a cyan head and a magenta head. . (A) is a schematic diagram of a cyan head, (b) is a schematic diagram of a magenta head, and (c) is a schematic diagram of dots at the time of dot size modulation from a cyan head and a magenta head. . (A) is a schematic diagram of a cyan head, (b) is a schematic diagram of a magenta head, and (c) is a schematic diagram of dots during adjacent dot size modulation.

<Embodiment>
Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an example of an image forming apparatus that outputs image data generated by an image processing method according to the present invention will be described with reference to FIGS. FIG. 1 is an explanatory side view for explaining the overall configuration of the mechanism of the image forming apparatus according to the embodiment. FIG. 2 is an explanatory plan view of a mechanism portion of the image forming apparatus shown in FIG.

  In the image forming apparatus, a carriage 3 is slidably held in a main scanning direction by a guide rod 1 and a guide rail 2 which are guide members horizontally mounted on left and right side plates (not shown). The main scanning motor 4 moves and scans in the direction indicated by the arrow (main scanning direction) in FIG. 2 via a timing belt 5 stretched between the driving pulley 6A and the driven pulley 6B.

  In the carriage 3, for example, four recording head units 7y, 7c, 7m, and 7k including liquid ejection heads that eject yellow (Y), cyan (C), magenta (M), and black (K) are arranged. ing. The four recording head units 7y, 7c, 7m, and 7k are mounted such that a plurality of ink ejection openings are arranged in a direction crossing the main scanning direction, and the ink droplet ejection direction is directed downward. However, when the colors are not distinguished, the recording head units 7y, 7c, 7m, and 7k are referred to as “recording heads 7”.

  In this embodiment, four colored inks are mounted. However, it is possible to mount other colors, and it is possible to mount other colors. It is also possible to mount the liquid.

  Examples of the liquid discharge head constituting the recording head 7 include a piezoelectric actuator such as a piezoelectric element, and a thermal actuator that uses a phase change caused by liquid film boiling using an electrothermal conversion element such as a heating resistor. In addition, the liquid discharge head includes a shape memory alloy actuator using a metal phase change due to a temperature change, an electrostatic actuator using an electrostatic force, etc. as pressure generating means for generating a pressure for discharging a droplet, etc. Can be used.

Further, the configuration is not limited to an independent head for each color, and may be configured with one or a plurality of liquid ejection heads having a nozzle row composed of a plurality of nozzles that eject droplets of a plurality of colors. In the present embodiment, the configuration of the serial printer as shown in FIG. 2 is adopted, but the configuration as shown in FIG. 3 may be used.
FIG. 3 is a conceptual diagram of a line-type printer having a head for covering the paper width and each color.

  Also, the carriage 3 shown in FIG. 2 is equipped with sub-tanks 8 for each color for supplying ink of each color to the recording head 7. Ink is supplied to the sub tank 8 from a main tank (ink cartridge) (not shown) via an ink supply tube 9.

  The paper feeding unit for feeding the paper 12 loaded on the paper stacking unit (pressure plate) 11 such as the paper feeding cassette 10 is a half-moon roller (paper feeding) that separates and feeds the paper 12 from the paper stacking unit 11 one by one. It is also called a roller.) A separation pad 14 made of a material having a large friction coefficient is provided opposite to 13. The separation pad 14 is biased toward the half-moon roller (feed roller) 13 side.

  The conveyance belt 21 conveys the sheet 12 by electrostatic adsorption so as to convey the sheet 12 fed from the sheet feeding unit below the recording head 7. The counter roller 22 conveys the sheet 12 fed from the sheet feeding unit via the guide 15 with the conveyance belt 21 interposed therebetween. The conveyance guide 23 changes the direction of the sheet 12 fed substantially vertically upward by approximately 90 ° to follow the conveyance belt 21. The pressing roller 25 is urged toward the conveying belt 21 by the pressing member 24. The charging roller 26 is charging means for charging the surface of the transport belt 21.

  Here, the conveyance belt 21 is an endless belt, and is stretched between the conveyance roller 27 and the tension roller 28, and the conveyance roller 27 rotates from the sub scanning motor 31 via the timing belt 32 and the timing roller 33. Is done. By this rotation, it is configured to go around in the belt conveyance direction (sub-scanning direction) in FIG.

A guide member 29 is disposed on the back side of the conveying belt 21 in correspondence with the image forming area formed by the recording head 7. The charging roller 26 is disposed so as to come into contact with the surface layer of the transport belt 21 and rotate following the rotation of the transport belt 21.
As shown in FIG. 2, a slit disk 34 is attached to the shaft of the conveying roller 27, and an encoder sensor 35 for detecting the slit of the slit disk 34 is provided. A rotary encoder 36 is constituted by 35.

  Further, as a paper discharge unit for discharging the paper 12 recorded by the recording head 7, a separation claw 51 for separating the paper 12 from the transport belt 21, a paper discharge driving roller 52 and a paper discharge roller 53, And a paper discharge tray 54 for stocking the paper 12 to be discharged.

A double-sided paper feeding unit is detachably attached to the back. This double-sided paper feeding unit takes in the paper 12 returned by the reverse rotation of the conveying belt 21, reverses it, and feeds it again between the counter roller 22 and the conveying belt 21.
Further, as shown in FIG. 2, a maintenance / recovery mechanism 56 for maintaining and recovering the nozzle state of the recording head 7 is disposed in the non-printing area on one side of the carriage 3 in the scanning direction.

  The maintenance / recovery machine 56 is used for discharging each cap 57 that caps each nozzle surface of the recording head 7, a wiper blade 58 that wipes the nozzle surface, and a droplet that does not contribute to recording because the thickened ink is discharged. An empty discharge receptacle 59 for receiving droplets is provided.

  In the image forming apparatus, the sheets 12 are separated and fed one by one from the sheet feeding unit, and the sheet 12 fed substantially vertically upward is guided by a guide 15 and sandwiched between a conveyance belt 21 and a counter roller 22. Are transported. In the image forming apparatus, the leading end is further guided by the transport guide 23 and pressed against the transport belt 21 by the pressing roller 25, and the transport direction is changed by approximately 90 °.

  At this time, an alternating voltage is applied from the AC bias supply unit to the charging roller 26 by a control unit (not shown), and plus and minus are alternately repeated at a predetermined width in the sub-scanning direction that is the circumferential direction of the transport belt 21. Electrified with a pattern. When the sheet 12 is fed onto the charged conveying belt 21, the sheet 12 is attracted to the conveying belt 21 by electrostatic force, and the sheet 12 is conveyed in the sub-scanning direction by the circular movement of the conveying belt 21.

  Therefore, by driving the recording head 7 in accordance with the image signal while moving the carriage 3 in the forward and backward directions, ink droplets are ejected onto the stopped paper 12 to record one line, and the paper 12 is After transporting a predetermined amount, the next line is recorded. Upon receiving a recording end signal or a signal that the trailing edge of the paper 12 has reached the recording area, the recording operation is terminated and the paper 12 is discharged onto the paper discharge tray 54.

  In the case of double-sided printing, the conveyance belt 21 is reversely rotated when the recording of the front surface (surface to be printed first) is completed. With this reverse rotation, the recorded paper 12 is fed into the double-sided paper feeding unit 61, and the paper 12 is reversed (with the back surface being the printing surface) and fed again between the counter roller 22 and the conveyor belt 21. Make paper. Timing control is performed, and the paper is transported onto the transport bell 21 and recorded on the back surface in the same manner as described above, and then discharged onto the paper discharge tray 54.

  During printing (recording) standby, the carriage 3 is moved to the maintenance / recovery mechanism 56 side, the nozzle surface of the recording head 7 is capped by the cap 57, and the nozzles are kept in a wet state. To prevent. In the state where the recording head 7 is capped with the cap 57, the ink is sucked from the nozzle, and the recovery operation is performed to discharge the thickened ink and bubbles. Wiping is performed by the wiper blade 58 in order to clean and remove ink adhering to the nozzle surface of the recording head 7 by this recovery operation. In addition, an idle ejection operation for ejecting ink not related to recording is performed before the start of recording or during recording. Thereby, the stable ejection performance of the recording head 7 is maintained.

  Here, 161 is a light emitting element, and 162 is a light receiving element, which detects the presence or absence of nozzle omission and the position of nozzle omission by irradiating and receiving ink droplets ejected from the nozzles. Since a plurality of methods for detecting missing nozzles are known, they are omitted in the present invention.

  Next, an example of the liquid discharge head constituting the recording head 7 will be described with reference to FIGS. FIG. 4 is an explanatory sectional view taken along the longitudinal direction of the liquid chamber of the recording head. FIG. 5 is a cross-sectional explanatory diagram of the recording head in the lateral direction of the liquid chamber (nozzle arrangement direction).

  The liquid discharge head includes a flow path plate 101, a vibration plate 102, a nozzle plate 103, a nozzle communication path 105, a liquid chamber (also referred to as a pressure chamber) 106, an ink supply port 109, and the like.

  The channel plate 101 is formed, for example, by anisotropic etching of a single crystal silicon substrate. A diaphragm 102 formed by, for example, nickel electroforming, bonded to the lower surface of the flow path plate 101, and a nozzle plate 103 bonded to the upper surface of the flow path plate 101 are bonded and laminated. In order to supply ink to the nozzle communication path 105 that is a flow path through which the nozzle 104 that discharges droplets (ink drops) communicates, the liquid chamber 106 that is a pressure generation chamber, and the liquid chamber 106 through the fluid resistance portion (supply path) 107. An ink supply port 109 and the like communicating with the common liquid chamber 108 are formed.

  In addition, two rows of stacked piezoelectric elements 121 as electromechanical conversion elements, which are pressure generating means (actuator means) for pressurizing the ink in the liquid chamber 106 by deforming the diaphragm 102, and the piezoelectric elements 121 are 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 a simple column.

Further, an FPC cable 126 equipped with a drive circuit (drive IC: Integrated Circuit) (not shown) is connected to the piezoelectric element 121.
The peripheral edge of the diaphragm 102 is joined to the frame member 130. The frame member 130 includes a penetrating portion 131 that houses an actuator unit composed of the piezoelectric element 121, the base substrate 122, and the like, a concave portion that becomes the common liquid chamber 108, and ink for supplying ink to the common liquid chamber 108 from the outside. A supply hole 132 is formed. The frame member 130 is formed by injection molding with a thermosetting resin such as an epoxy resin or polyphenylene sulfite, for example.

  Here, the channel plate 101 is formed by, for example, anisotropically etching a single crystal silicon substrate having a crystal plane orientation (110) using an alkaline etching solution such as an aqueous potassium hydroxide solution (KOH), so that the nozzle communication path 105, A recess or a hole to be the liquid chamber 106 is formed. However, the substrate is not limited to a single crystal silicon substrate, and other stainless steel substrates, photosensitive resins, and the like can be used.

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

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

The piezoelectric element 121 is a laminated piezoelectric element (here, PZT: lead zirconate titanate) in which piezoelectric materials 151 and internal electrodes 152 are alternately laminated. An individual electrode (also referred to as a selection electrode) 153 and a common electrode 154 are connected to each internal electrode 152 drawn out to different end faces of the piezoelectric element 121.
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 liquid chamber is configured using the displacement in the d31 direction as the piezoelectric direction of the piezoelectric element 121. A configuration may be adopted in which the ink in 106 is pressurized. Further, a structure in which one row of piezoelectric elements 121 is provided on one substrate 122 may be employed.

  In the liquid discharge head configured as described above, the piezoelectric element 121 contracts, for example, by lowering the voltage applied to the piezoelectric element 121 from the reference potential. As the diaphragm 102 descends and the volume of the liquid chamber 106 expands, the 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 direction of the nozzle 104 to contract the volume / volume of the liquid chamber 106. Ink is pressurized. As a result, ink droplets are ejected (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. 106 is filled with ink.
Therefore, after the vibration of the meniscus surface of the nozzle 104 is attenuated and stabilized, the operation proceeds to the next droplet discharge.

Note that the driving method of the head is not limited to the above example (drawing-pushing), and it is also possible to perform the striking, pushing, etc. depending on the direction of the drive waveform.
Next, an outline of the control unit of the image forming apparatus will be described with reference to the block diagram of FIG.

FIG. 6 shows an example of a functional block diagram of the image forming apparatus shown in FIG.
The image forming apparatus includes an operation unit 71, a display unit 72, a sheet feeding unit 73, a conveyance unit 74, a first discharge unit 75, a second discharge unit 76, a detection unit 77, a paper discharge unit 78, and a control unit 79. The operation means 71 is a device having switches such as a power switch, a numeric keypad, a start key, and a stop key necessary for a user to operate the image forming apparatus, and is realized by an operation panel.

  The display unit 72 is a member such as a display element or a lamp necessary for the user to operate the image forming apparatus, and is realized by an operation panel.

  The paper feeding means 73 is means for taking out the paper 12 from the paper feeding cassette 10, and is realized by the half-moon roller 13 and the separation pad 14 shown in FIG. The conveying means 74 is means for conveying the paper 12 to the first discharge means 75 and the second discharge means 76, and is realized by various motors 2000 shown in FIG. The first ejection means 75 as the first recording head and the second ejection means 76 as the second recording head are means for ejecting ink as droplets onto the paper 12, and the recording head 7 shown in FIG. It is realized by.

  The detecting means 77 is a detecting means for detecting a defective nozzle in the first recording head and the second recording head, and is realized by the light emitting element 161 and the light receiving element 162 shown in FIG. The paper discharge means 78 is a means for discharging the printed paper 12, and is realized by the paper discharge drive roller 52, the paper discharge roller 53, the separation claw 51, and the paper discharge tray 54 shown in FIG. The control unit 79 is a unit that performs overall control of the image forming apparatus, and is realized by the CPU 701, the image processing unit 810, the FPGA 702, the RAM 703, the ROM 704, and the NVRAM 705 illustrated in FIG.

  FIG. 7 is a block diagram illustrating a hardware configuration example of the image forming apparatus 600 of the present embodiment. The image forming apparatus 600 includes a main control board 700, a head relay board 900, and an image processing board 800.

  The main control board 700 includes a CPU (Central Processing Unit) 701, FPGA (Field-Programmable Gate Array) 702, RAM (Random Access Memory) 703, ROM (Read Only Memory) 704, NVRAM (Non-Volatile Random Access Memory) 705, a motor driver 706, a drive waveform generation circuit 707, and the like are mounted.

  The CPU 701 governs overall control of the image forming apparatus 600. For example, the CPU 701 uses the RAM 703 as a work area, executes various control programs stored in the ROM 704, and outputs control commands for controlling various operations in the image forming apparatus 600. At this time, the CPU 701 controls various operations in the image forming apparatus 600 in cooperation with the FPGA 702 while communicating with the FPGA 702.

  The FPGA 702 includes a CPU control unit 711, a memory control unit 712, an I2C control unit 713, a sensor processing unit 714, a motor control unit 715, and a recording head control unit 716.

  The CPU control unit 711 has a function of communicating with the CPU 701. The memory control unit 712 has a function of accessing the RAM 703 and the ROM 704. The I2C control unit 713 has a function of communicating with the NVRAM 705.

The sensor processing unit 714 performs processing of sensor signals of various sensors 9000. The various sensors 9000 are generic names of sensors that detect various states in the image forming apparatus 600. In addition to the encoder sensor 35 described above, the various sensors 9000 include a paper sensor for detecting the passage of the recording paper P, a cover sensor for detecting the opening of the cover member, a temperature / humidity sensor for detecting environmental temperature and humidity, and the recording paper P. A sheet fixing lever sensor for detecting the operation state of the fixing lever, a remaining amount detecting sensor for detecting the remaining ink amount of the cartridge 7, and the like are included.
Note that an analog sensor signal output from a temperature / humidity sensor or the like is converted into a digital signal by an AD converter mounted on the main control board 700 or the like and input to the FPGA 702, for example.

  The motor control unit 715 controls various motors 2000. The various motors 2000 are generic names of motors included in the image forming apparatus 600. Various motors 2000 operate a main scanning motor for operating the carriage, a sub-scanning motor for transporting the recording paper P in the sub-scanning direction, a paper feeding motor for feeding the recording paper P, and a maintenance mechanism 15 A maintenance motor for the purpose is included.

Here, a specific example of control by cooperation between the CPU 701 and the motor control unit 715 of the FPGA 702 will be described by taking operation control of the main scanning motor 8 as an example.
First, the CPU 701 notifies the motor control unit 715 of the operation speed and distance of the carriage 5 together with an operation start instruction for the main scanning motor 8. Receiving this instruction, the motor control unit 715 generates a drive profile based on the movement speed and movement instruction information notified from the CPU 701, and generates an encoder value (sensor signal of the encoder sensor 35) supplied from the sensor processing unit 714. The PWM command value is calculated and output to the motor driver 706 while comparing with the value obtained by processing the above. The motor control unit 715 notifies the CPU 701 of the end of the operation when the predetermined operation ends.
Although an example in which the motor control unit 715 generates a drive profile has been described here, a configuration in which the CPU 701 generates a drive profile and instructs the motor control unit 715 may be employed. The CPU 701 also counts the number of printed sheets and counts the number of scans of the main scanning motor 8.

  The recording head control unit 716 passes the head drive data, the discharge synchronization signal LINE, and the discharge timing signal CHANGE stored in the ROM 704 to the drive waveform generation circuit 707, and causes the drive waveform generation circuit 707 to generate a common drive waveform signal Vcom. The common drive waveform signal Vcom generated by the drive waveform generation circuit 707 is input to a recording head driver 210 (described later) mounted on the head relay substrate 900.

  Next, an example of the print control unit 207 and the head driver 208 will be described with reference to FIG.

FIG. 8 is a block diagram illustrating a configuration example of the recording head control unit 910, the drive waveform generation circuit 707, and the recording head driver 210.
When the recording head controller 910 receives the trigger signal Trig that triggers the ejection timing, it outputs the ejection synchronization signal LINE that triggers the generation of the drive waveform to the drive waveform generation circuit 707. Further, a discharge timing signal CHANGE corresponding to the delay amount from the discharge synchronization signal LINE is output to the drive waveform generation circuit 707 (see FIG. 8).
The drive waveform generation circuit 707 generates a common drive waveform Vcom at a timing based on the discharge synchronization signal LINE and the discharge timing signal CHANGE.
Further, the recording head control unit 910 receives image data SD ′ after image processing from an image processing unit 810, which will be described later, provided on the image processing substrate 800. The recording head control unit 910 generates a mask control signal MN for selecting a predetermined waveform of the common drive waveform signal Vcom according to the size of the ink droplets ejected from each nozzle of the recording head 7 based on the image data SD ′. Generate. The mask control signal MN is a signal having a timing synchronized with the ejection timing signal CHANGE. Then, the recording head control unit 910 transfers the image data SD ′, the synchronization clock signal SCK, the latch signal LT instructing to latch the image data, and the generated mask control signal MN to the recording head driver 210.

  As shown in FIG. 8, the recording head driver 210 includes a shift register 211, a latch circuit 212, a gradation decoder 213, a level shifter 214, and an analog switch 215.

  The shift register 211 receives the image data SD ′ and the synchronous clock signal SCK transferred from the recording head control unit 910. The latch circuit 212 latches each registration value of the shift register 211 by a latch signal LT transferred from the recording head control unit 910.

  The gradation decoder 213 decodes the value (image data SD ′) latched by the latch circuit 212 and the mask control signal MN, and outputs the result. The level shifter 214 converts the logic level voltage signal of the gradation decoder 213 to a level at which the analog switch 215 can operate.

  The analog switch 215 is a switch that is turned on / off by the output of the gradation decoder 213 given through the level shifter 214. The analog switch 215 is provided for each of the nozzles included in the recording head 7, and is connected to the individual electrode 83 of the piezoelectric element 70 corresponding to each nozzle. The analog switch 215 receives the common drive waveform signal Vcom from the drive waveform generation circuit 707. Further, as described above, the timing of the mask control signal MN is synchronized with the timing of the common drive waveform Vcom. Accordingly, the on / off of the analog switch 215 is switched at an appropriate timing in accordance with the output of the gradation decoder 213 given through the level shifter 214, whereby each nozzle is selected from the drive waveforms constituting the common drive waveform signal Vcom. The waveform applied to the piezoelectric element 70 corresponding to is selected. As a result, the size of the ink droplet ejected from the nozzle is controlled.

  From the drive waveform generation circuit 707, as shown in FIG. 9, within one printing cycle (one drive cycle), a waveform element falling from the reference potential Ve, a waveform element rising from the state after the falling, etc. are faired. A drive signal composed of the drive pulses P1 to P8 is generated and output.

  On the other hand, the driving pulse to be used is selected by the mask signal MN from the recording head control unit 910.

  Here, the waveform element in which the potential V of the drive pulse falls from the reference potential Ve is a pull-in waveform element in which the piezoelectric element 121 contracts and the volume of the liquid chamber 106 expands. 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 liquid chamber 106 to contract.

FIG. 10A is an explanatory diagram for explaining a small droplet selected from the drive waveform, FIG. 10B is a diagram illustrating a medium droplet selected from the drive waveform, and FIG. It is explanatory drawing for. FIG. 10C is an explanatory diagram for explaining a large droplet selected from the driving waveform, and FIG. 10D is an explanatory diagram for explaining fine driving selected from the driving waveform.
When a droplet (small dot) is formed by the mask control signal MN from the recording head controller 910, the drive pulse P1 is selected as shown in FIG. When forming medium drops (medium dots), the drive pulses P4 to P6 are selected as shown in FIG. When forming large droplets (large dots), the drive pulses P2 to P8 are selected as shown in FIG. When fine driving is performed (the meniscus is vibrated without droplet ejection), a fine driving pulse P2 is selected and applied to the piezoelectric element 121 of the recording head 7 as shown in FIG.

  When forming a medium droplet, the first droplet is ejected by the driving pulse P4, the second droplet is ejected by the driving pulse P5, and the third droplet is ejected by the driving pulse P6. At this time, assuming that the natural vibration period of the liquid chamber 106 is Tc, the interval between the ejection timings of the drive pulses P4 and P5 is preferably 2Tc ± 0.5 μs.

  Since the drive pulses P4 and P5 are composed of simple strike waveform elements, if the drive pulse P6 is also set to the same simple strike waveform element, the ink droplet speed becomes too large, and the landing positions of other droplet types There is a risk of shifting.

  Therefore, the drive pulse P6 reduces the pull-in voltage (decreases the falling potential) to reduce the pull-in of the meniscus and suppress the ink drop speed of the third drop. However, the startup voltage is not reduced in order to increase the necessary ink droplet volume.

  That is, in the drawing waveform element of the final drive pulse among the plurality of drive pulses, by reducing the drawing voltage relatively, the droplet discharge speed by the final drive pulse is relatively reduced, and the landing position is set to other droplets. It can be combined with the seed as much as possible.

  The fine drive pulse P2 is a drive waveform that vibrates the meniscus without ejecting ink droplets in order to prevent the meniscus of the nozzle from drying. This fine driving pulse P2 is applied to the recording head 7 in the non-printing area. Further, by using the drive pulse P2 that is the fine drive waveform as one of the drive pulses constituting the large droplet, the drive cycle can be shortened (speeded up).

  Furthermore, by setting the interval between the ejection timings of the fine drive pulse P2 and the drive pulse P3 within the range of the natural vibration period Tc ± 0.5 μs, the volume of ink droplets ejected by the drive pulse P3 can be increased. That is, the droplet volume of the droplet that can be ejected by the drive pulse P3 is applied by the drive pulse P3 alone by superimposing the expansion of the liquid chamber 106 by the drive pulse P3 on the pressure vibration of the liquid chamber 106 by the vibration cycle generated by the fine drive pulse P2. You can make it larger than you want.

The required drive waveform varies depending on the viscosity of the ink. Accordingly, as shown in FIG. 11, in the image forming apparatus, a drive waveform when the ink viscosity is 5 mPa · s, a drive waveform when the viscosity is 10 mPa · s, and a drive waveform when the viscosity is 20 mPa · s are prepared. . The ink viscosity is determined from the detected temperature from the temperature sensor, and the drive waveform to be used is selected.
FIG. 11 is an explanatory diagram for explaining a drive waveform according to the viscosity of the ink.

  That is, when the ink viscosity is small, the voltage of the drive pulse is relatively small, and when the ink viscosity is large, the voltage of the drive pulse is relatively large. The volume can be discharged substantially constant. Further, the driving pulse can vibrate the meniscus without ejecting ink droplets by selecting the peak value according to the ink viscosity.

  By using a drive waveform composed of such drive pulses, it is possible to control the time until each large, medium, and small droplet lands on the paper, and the ejection start time differs for each large, medium, and small droplet. In addition, each drop can be landed at substantially the same position.

  FIG. 12 is a functional block diagram illustrating a configuration example of the image processing unit 810.

  The image processing unit 810 performs gradation processing, image conversion processing, and the like on the received image data, and converts the image data into a format that can be processed by the recording head control unit 716. Then, the image processing unit 810 outputs the converted image data to the recording head control unit 716.

  Specifically, the image processing unit 810 includes an interface 41, a gradation processing unit 42, an image conversion unit 43, and an image processing unit RAM 44.

  The interface 41 is an image data input unit, and is a communication interface with the CPU 701 and the FPGA 702. The gradation processing unit 42 performs gradation processing on the received multi-valued image data and converts it to small-valued image data. The small-value image data is image data having the same number of gradations as the types of droplets (large droplets, medium droplets, small droplets) ejected by the recording head 7 shown in FIG. The gradation processing unit 42 holds the converted image data on the image processing unit RAM 44 for one band or more. The image data for one band refers to image data corresponding to the maximum width in the sub-scanning direction that can be recorded by the recording head 7 in one scan in the main scanning direction X.

  The image conversion unit 43 converts the image data of one band on the image processing unit RAM 44 in units of images to be output in one scan (one scan) in the main scanning direction X. This conversion is performed in accordance with the configuration of the recording head 7 in accordance with the information on the printing order and the printing width (= sub-scanning width of image recording per scan) received from the CPU 701 via the interface 41.

  The printing order and the printing width may be one-pass printing in which an image is formed by one main scanning on the recording medium, and the same area of the recording medium may be performed a plurality of times by the same nozzle group or different nozzle groups. Multi-pass printing for forming an image may be used. Further, the heads may be arranged in the main scanning direction, and the same area may be divided by different nozzles. These recording methods can be used in appropriate combination.

  The print width indicates the width in the sub-scanning direction Y of the image recorded by the scanning of the recording head 7 in the main scanning direction X (one scan). In this embodiment, the CPU 701 sets the print width.

  The image conversion unit 43 outputs the converted image data SD ′ to the image recording unit 50 via the interface 41.

The function of the image processing unit 810 may be executed as a hardware function such as an FPGA or an ASIC, or may be executed by an image processing program stored in a storage device inside the image processing unit 810.

  Next, an image forming method according to the present invention for outputting a print image by the above-described image forming apparatus will be described below with respect to an image processing apparatus in which a program according to the present invention is installed in a computer and the image forming apparatus.

An example of an image forming system according to the present invention constituted by the image processing apparatus according to the present invention and the ink jet printer (ink jet recording apparatus) as the image forming apparatus described above will be described with reference to FIG.
FIG. 13 is an explanatory block diagram illustrating an example of an image forming system according to the present invention.
This printing system (image forming system) is configured by connecting one or a plurality of image processing apparatuses 400 including a personal computer (PC) or the like and an image forming apparatus 600 via a predetermined interface or network.

As shown in FIG. 14, in the image processing apparatus 400, a CPU 401 and various ROMs 402 and RAM 403, which are memory means, are connected by a bus line. A storage device 406 using a magnetic storage device such as an HDD, an input device 404 such as a mouse and a keyboard, a monitor 405 such as an LCD and a CRT, and a storage medium such as an optical disk (not shown) are connected to the bus line via an interface. A storage medium reader for reading is connected. Here, HDD is an abbreviation for Hard Disk Drive, LCD is an abbreviation for Liquid Crystal Display, and CRT is an abbreviation for Cathode Ray Tube.
In addition, a predetermined interface (external I / F) 407 that communicates with a network such as the Internet or an external device such as a USB (universal serial bus) is connected.

In the image processing apparatus 400, an image drawing or character recording command from an application or an operating system is temporarily stored in a drawing data memory. Note that the recording command is, for example, a description of the position, thickness, and shape of a line to be recorded, or a typeface, size, position, etc. of a character to be recorded. These commands are written in a specific print language. It is described.
The command stored in the drawing data memory is interpreted by the rasterizer, and if it is a line recording command, it is converted into a recording dot pattern corresponding to the designated position and thickness. If the instruction is a character recording instruction, the outline information of the corresponding character is called from the font outline data stored in the image processing apparatus 400 and converted into a recording dot pattern corresponding to the designated position and size. If the command is image data, it is converted into a recording dot pattern as it is.

  These recorded dot patterns are subjected to image processing and stored in a raster data memory. At this time, the image processing apparatus 400 rasterizes the data into recording dot pattern data using the orthogonal lattice as a basic recording position. Image processing includes, for example, color management processing (CMM) for adjusting colors, γ correction processing, halftone processing such as dithering and error diffusion, further background removal processing, total ink amount regulation processing, and the like.

  The recording dot pattern stored in the raster data memory is transferred to the ink jet recording apparatus via the interface.

An image processing program is stored in the storage device 406 of the image processing apparatus 400. This image processing program is installed in the storage device 406 by being read from a storage medium by a storage medium reader or downloaded from a network such as the Internet.
By this installation, the image processing apparatus 400 becomes operable to perform the following image processing. Note that this image processing program may operate on a predetermined OS (Operating System). Further, it may be a part of specific application software.

This image processing method can also be implemented on the image forming apparatus side, but the ink jet recording apparatus side has a function of generating a dot pattern to be actually recorded in response to an image drawing or character print command in the apparatus. This will be described using an example that does not have this.
That is, a print command from application software or the like executed by the image processing apparatus 400 serving as a host computer is subjected to image processing by the printer driver according to the present invention incorporated as software in the image processing apparatus 400. An example in which multi-value dot pattern data (print image data) that can be output by an inkjet printer after image processing is generated for each color plate, rasterized, transferred to the inkjet printer, and printed out by the inkjet printer will be described. .

FIG. 15 is a flowchart of nozzle missing check performed on the main control board 700 of the control means 79 of the ink jet printer.
First, the detection means 77 in the ink jet printer checks whether or not there is a missing nozzle for each color plate (step S11). If there is no nozzle omission, the process ends (step S12 / No). If there is a nozzle missing (step S12 / Yes), the main control board 700 notifies the image processor 810 of nozzle missing information (step S13). The nozzle missing information includes position information of nozzles with missing nozzles.

FIG. 16 is an example of a flowchart of nozzle omission correction performed on the image processing substrate 800 of the control means 79 of the inkjet printer.
The image processing unit 810 converts the multivalued image data recording head 7 inputted from the image processing apparatus 400 into image data of the number of gradations to be ejected, and stores it in the FPGA 702 as image data SD ′ that matches the configuration of the recording head 7. This correction flow is performed when the output process is performed.
The image processing unit 810 stores nozzle missing information notified from the ink jet printer in the image processing unit RAM 44.
When the correction flow is started, first, the presence of nozzle missing is checked from the information stored in the image processing unit RAM 44 (step S1). If there is no nozzle missing, the flow ends (step S2 / No).
If there is a missing nozzle (step S2 / Yes), the gradation processing unit 42 performs correction for modulating the dot size of the adjacent dot of the dot corresponding to the missing nozzle in the image for each color plate converted by the image converting unit 43. . Since the image conversion unit 43 generates image data according to the configuration of the recording head 7, the image conversion unit 43 can specify which dot corresponds to the missing nozzle. Details of the dot size modulation will be described later. The dot size is modulated for each color plate (step S3).
Next, the gradation processing unit 42 performs superimposition of images that have been subjected to dot size modulation for each color plate (step S4). As a result of superimposing the images for each color plate, it is confirmed whether or not there is a dot size modulation part in the same pixel (step S5). If there is no dot size modulation part in the same pixel (step S5 / No), processing Exit. If there is a dot size modulation section in the same pixel, the dot size modulation width is reduced to prevent an excessive ink adhesion amount (step S5 / Yes).

Next, a first embodiment of nozzle missing correction will be described below.
First, normal nozzle omission correction will be described with reference to FIGS. 17 (a), (b), and (c).
FIG. 17A is a schematic diagram of the head, FIG. 17B is a schematic diagram of dots without nozzle omission correction, and FIG. 17C is a schematic diagram of dots during adjacent dot size modulation.
If the center nozzle of the head is non-ejection and there is no nozzle missing correction, there will be no white dot because there is no dot in the center, but by modulating the dot diameter of the adjacent part of the nozzle missing part to a larger size The visibility of white stripes accompanying nozzle missing can be reduced.

The nozzle omission correction when printing a secondary color will be described with reference to FIGS. 18A, 18B, and 19C to FIGS. 19A, 19B, and 19C.
FIG. 18A is a schematic diagram of a cyan head, FIG. 18B is a schematic diagram of a magenta head, and FIG. 18C is a diagram of dot size modulation from a cyan head and a magenta head. It is a dot schematic diagram. FIG. 19A is a schematic diagram of a cyan head, FIG. 19B is a schematic diagram of a magenta head, and FIG. 19C is a diagram of dot size modulation from a cyan head and a magenta head. It is a dot schematic diagram.

Here, a case where cyan and magenta are used is illustrated.
FIGS. 18C and 19C show a case where the central nozzle of the heads of both the cyan and magenta heads fail to eject.

FIGS. 18A to 18C show the nozzle missing correction performed in FIGS. 17A to 17C for each color plate.
When printing cyan and magenta as a single unit, the white line visibility can be reduced by correcting the missing nozzles. However, when printing red with cyan and magenta superimposed, the amount of ink adhering to the pixels with the larger dot size becomes excessive, and if the recording medium exceeds the allowable ink amount, transfer to the back due to ink loss or insufficient drying, etc. Will occur.

  Therefore, in the present invention, as shown in FIG. 19, when a plurality of colors are shot in the same pixel, the ink adhesion amount is controlled by reducing the modulation width of the dot size.

When cyan in FIG. 19A is printed alone, white streaks can be seen. However, when cyan and magenta are overlapped, the amount of liquid drops is two drops, so the nozzle missing portion is filled on the recording medium, and white streaks are observed. Visibility can be reduced.
Here, the case of two colors is illustrated, but, for example, when nozzle missing at the same location occurs in four-color superposition, the ink adhesion amount is controlled by further reducing the dot size modulation width. Just do it.
In addition, although the modulation widths of both colors are reduced here, if no problem occurs in the color or the like, the modulation width of any one of the colors may be reduced.

20A is a schematic diagram of a cyan head, FIG. 20B is a schematic diagram of a magenta head, and FIG. 20C is a schematic diagram of dots at the time of adjacent dot size modulation. .
FIG. 20C also shows a case where an image is formed using cyan and magenta, but the case where the cyan and magenta driving positions do not overlap will be described.
For example, since the generation of dots is sparse in a highlight area or the like, it is often seen that a plurality of colors are not superimposed on the same pixel.

  By having both the process of FIG. 19C and the process of FIG. 20C, it is possible to effectively perform nozzle omission correction.

In the above-described first embodiment, the correction flow according to the present invention is performed by the image processing unit 810, but may be performed by the image processing apparatus 400.
In this case, the image processing apparatus 400 stores the recording method information such as the configuration of the recording head 7 and the printing order and printing width by some method. For example, the configuration information of the recording head 7 may be stored when a program is installed in the image processing apparatus 400. The information on the recording method may be determined and stored when printing is instructed by the user.
The nozzle missing information is transmitted from the inkjet printer to the image processing apparatus 400 after detecting the nozzle missing.

In the above-described embodiment, the serial type printer in which the recording head 7 is mounted on the carriage and moves on the paper has been described. However, the present invention is also applicable to a line type printer in which the paper whose position of the recording head 7 is fixed moves. Is possible.

<Program>
The image forming apparatus according to the present invention described above is realized by a program that causes a computer to execute processing. As an example, the case where the function of the present invention is realized by a program will be described below.

For example,
A computer-readable program for an image forming apparatus including at least a first recording head and a second recording head,
On the computer,
A procedure in which the detecting means detects a defective nozzle in the first recording head and the second recording head;
When the control unit has the same landing position of the droplet from the defective nozzle of the first recording head as that of the droplet from the defective nozzle of the second recording head, A procedure for controlling the droplet volume discharged from the adjacent nozzle and the droplet volume discharged from the nozzle adjacent to the defective nozzle of the second recording head;
A program for executing

  Such a program may be stored in a computer-readable storage medium.

<Storage medium>
Here, examples of the storage medium include computer-readable storage media such as CD-ROM, flexible disk (FD), and CD-R, semiconductor memories such as flash memory, RAM, ROM, and FeRAM, and HDD.

  CD-ROM is an abbreviation for Compact Disc Read Only Memory. Flexible disk means Flexible Disk (FD). CD-R is an abbreviation for CD Recordable. FeRAM is an abbreviation for Ferroelectric RAM and means a ferroelectric memory.

<Effect>
As described above, according to the present embodiment, the droplet amount ejected from the nozzle adjacent to the defective nozzle of the first recording head and the droplet droplet ejected from the nozzle adjacent to the defective nozzle of the second recording head. Control the amount. In other words, in different heads, it is detected that a nozzle for ejecting droplets at the same pixel position is missing, and the droplet amount of adjacent nozzles is controlled. As a result, it is possible to reduce the visibility of white stripes due to missing nozzles and to form a high-quality image on the recording medium by controlling the ink adhesion amount on the recording medium.

  The above-described embodiment shows an example of a preferred embodiment of the present invention, and the present invention is not limited thereto, and various modifications can be made without departing from the scope of the invention. is there. For example, in the above description, the case where two recording heads are used for correction has been described. However, the present invention is not limited to this, and three or more recording heads used for correction may be used.

DESCRIPTION OF SYMBOLS 1 Guide rod 2 Guide rail 3 Carriage 7 Recording head 8 Sub tank 10 Paper feed cassette 11 Paper loading part (pressure plate)
12 paper 13 half moon roller (feed roller)
14 Separation Pad 15 Guide 21 Conveying Belt 22 Counter Roller 23 Conveying Guide 24 Holding Member 25 Holding Roller 26 Charging Roller 27 Conveying Roller 28 Tension Roller 29 Guide Member 31 Sub-Scanning Motor 32 Timing Belt 33 Timing Roller 34 Slit Disc 35 Encoder Sensor 36 Rotary encoder 41 Interface 42 Gradation processing unit 43 Image conversion unit 44 Image processing unit RAM
51 Separation Claw 52 Paper Discharge Drive Roller 53 Paper Discharge Roller 56 Maintenance Recovery Mechanism 57 Cap 101 Channel Plate 102 Vibration Plate 103 Nozzle Plate 104 Nozzle 105 Nozzle Communication Path 106 Liquid Chamber (Pressure Chamber)
108 Common liquid chamber 161 Light emitting element 162 Light receiving element 210 Recording head driver 400 Image processing device 700 Main control board 701 CPU
702 FPGA
703 RAM
704 ROM
705 NVRAM
706 Motor drive 707 Drive waveform generation circuit 711 CPU control unit 712 Memory control unit 713 I2C control unit 714 Sensor processing unit 715 Motor control unit 716 Recording head control unit 800 Image processing substrate 810 Image processing unit 900 Head relay substrate 910 Recording head control unit

JP 2002-86767 A

Claims (6)

An image forming apparatus including at least a first recording head and a second recording head,
Detecting means for detecting a defective nozzle in the first recording head and the second recording head;
When the landing position of the droplet from the defective nozzle of the first recording head is the same as the landing position of the droplet from the defective nozzle of the second recording head, the defective nozzle of the first recording head Control means for controlling the droplet volume discharged from the adjacent nozzle and the droplet volume discharged from the nozzle adjacent to the defective nozzle of the second recording head;
An image forming apparatus comprising:   2. The control unit according to claim 1, wherein the control unit confirms the position of the missing nozzle for each color plate, and if the same portion is missing, the dot size of the droplets ejected from the adjacent nozzle is increased. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the control unit corrects the missing nozzle only when a plurality of colors overlap the same pixel.   More than the case where the landing position of the droplet from the defective nozzle of the first recording head and the landing position of the droplet from the defective nozzle of the second recording head are the same, the first recording head has the When the landing position of the droplet from the defective nozzle is different from the landing position of the liquid droplet from the defective nozzle of the second recording head, the amount of droplet discharged from the nozzle adjacent to the defective nozzle is larger. The image forming apparatus according to claim 1. An image forming method in an image forming apparatus including at least a first recording head and a second recording head,
Detecting a defective nozzle in the first recording head and the second recording head;
When the landing position of the droplet from the defective nozzle of the first recording head is the same as the landing position of the droplet from the defective nozzle of the second recording head, the defective nozzle of the first recording head An image forming method comprising: controlling a droplet amount ejected from an adjacent nozzle and a droplet amount ejected from a nozzle adjacent to a defective nozzle of the second recording head. A computer-readable program for an image forming apparatus including at least a first recording head and a second recording head,
In the computer,
A procedure in which the detecting means detects a defective nozzle in the first recording head and the second recording head;
When the landing position of the droplet from the defective nozzle of the first recording head is the same as the landing position of the droplet from the defective nozzle of the second recording head, the control means A procedure for controlling a droplet amount discharged from an adjacent nozzle of the defective nozzle and a droplet amount discharged from a nozzle adjacent to the defective nozzle of the second recording head;
A program for running

Images