JP2009202337A - Image formation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that the maintenance (maintenance recovery) and interchange of heads which have been interchanged and then a printing will stop when a poor delivery generates with a spare head even adopting the configuration equipped with the spare head. <P>SOLUTION: Two or more head units 11 equipped with heads for discharging droplets are arranged and enable the printing of a printing area by one pass. The head unit 11 is movably installed between the image forming position corresponding to the printing area and the maintenance position for the maintenance recovery, and is equipped with the first droplet detection means 401 for detecting the droplet discharged from the head unit 11 located in the image forming position during printing, and the second droplet detection means 402 for detecting the droplet discharged at the time of the head unit 11 being located in the maintenance position. The discharged droplet is detected by the second droplet detection means 402 before moving the head unit 11 to the image forming position from the maintenance position, and then the discharge state of the head unit 11 is detected. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  As an image forming apparatus such as a printer, a facsimile machine, a copying apparatus, a plotter, and a complex machine of these, for example, an ink jet recording apparatus is known as an image forming apparatus of a liquid discharge recording method using a recording head for discharging ink droplets. . This liquid discharge recording type image forming apparatus means that ink droplets are transported from a recording head (not limited to paper, including OHP, and can be attached to ink droplets and other liquids). Yes, it is also ejected onto a recording medium or a recording medium, recording paper, recording paper, etc.) to form an image (recording, printing, printing, and printing are also used synonymously). And a serial type image forming apparatus that forms an image by ejecting liquid droplets while the recording head moves in the main scanning direction, and a line type head that forms images by ejecting liquid droplets without moving the recording head There are line type image forming apparatuses using

  The “image forming apparatus” means an apparatus that forms an image by discharging liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, etc. “Formation” means not only giving an image having a meaning such as a character or a figure to a medium but also giving an image having no meaning such as a pattern to the medium (simply ejecting a droplet). means. Further, “ink” is not limited to ink in a narrow sense, and is not particularly limited as long as it becomes liquid when ejected. For example, a DNA sample, a resist, a pattern material, a resin material, etc. Is also included.

  In such a liquid ejection type image forming apparatus, it is possible to form a pattern in a non-contact manner on a medium by ejecting liquid droplets from a number of pores called many nozzles of a liquid ejection head. Therefore, it is possible to form an image by a single image forming process regardless of the type and shape of the medium.

  Since this nozzle has a fine orifice having a diameter of 50 μm or less and ejects a droplet from the orifice, it is very difficult to keep it in a normal state. In particular, in the case of a line-type head having a nozzle row in which nozzles corresponding to the medium width are arranged, the number of nozzles is enormous, from several hundred to several thousand. It is an important problem to avoid the state where the liquid droplets are not ejected in the vertical direction and the state where the ejected droplets cannot form a desired size, and to keep everything normal.

Therefore, as described in Patent Document 1, it is known to replace a head in a defective discharge state with another head, and to proceed with cleaning of the defective discharge head during that time.
Japanese Patent No. 3944858

Further, in order to normalize the nozzle state, it is necessary to identify a nozzle with defective ejection and perform a recovery operation. In a conventional inkjet printer or the like, a nozzle check pattern is printed on a paper surface to visually check the nozzle state. However, the paper is wasted and it is necessary to get used to the confirmation. Therefore, as described in Patent Document 2, a device for checking the discharge state by checking the droplets ejected from the nozzle optically has been put into practical use, for example, mounted on a wide format inkjet plotter or the like. ing.
JP 2006-187981 A

Further, in the conventional serial type image forming apparatus, as described in Patent Document 3, a discharge state detection device is provided in the vicinity of an empty discharge receiver that discharges droplets that do not contribute to image formation.
JP 2005-319698 A

On the other hand, in the line type image forming apparatus, the head portion does not need to move in a printing state and is stationary. Therefore, in Patent Document 4, a discharge detection device is provided in a cap member of a maintenance / recovery device that performs head maintenance / recovery, and droplets are detected when the head unit is moved to a position where a maintenance / recovery operation is performed. It is described that.
Japanese Patent No. 2838894

Japanese Patent Application Laid-Open No. H10-228561 describes that an apparatus for detecting the ejection state is arranged on a path that moves to a position for performing the head maintenance and recovery operation.
Japanese Patent Laid-Open No. 2005-199658

  In recent years, high-speed printing has been demanded, and a line-type inkjet apparatus that performs printing in one pass by arranging inkjet nozzles in the paper width direction of the printing area has been put into practical use. Line-type ink jet devices are easy to increase in size because the head is required for the width of the paper, and it is difficult to maintain reliability because of the large number of nozzles ejected simultaneously.

For this reason, the ink on the nozzle surface is discharged to a location unrelated to printing, or the discharge detection is performed to improve the reliability. However, if discharge failure occurs, printing is stopped for maintenance. There is a need. In order to avoid this point, Patent Documents 6 and 7 disclose a method in which a plurality of heads are provided and replaced with alternative heads during maintenance.
Japanese Patent Laid-Open No. 07-076093 Japanese Patent No. 3,906,631

  However, in these Patent Documents 6 and 7, since an alternative head is required for the width of the paper, the size becomes large and the apparatus becomes large. In addition, having a spare head that is not used for normal printing reduces the printing amount per nozzle and increases the cost of the apparatus.

Therefore, Patent Document 8 discloses a configuration in which printing is performed while replacing a small auxiliary head by dividing into a plurality of heads with respect to the paper width and reducing the replacement unit.
Japanese Patent No. 3944858

  As described above, in the line-type image forming apparatus, even if a configuration including a spare head as described in the above-mentioned patent document for continuous printing is adopted, the ejection state of the spare head is completely ( Is not necessarily good). For this reason, if an ejection failure occurs after replacement of the spare head, maintenance (maintenance recovery) and replacement work of the replaced head are required, and printing stops, resulting in line-type high-speed printing (productivity). There is a problem of being damaged.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to improve the reliability with respect to ejection failure so that the head can be used efficiently.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A plurality of head units having a head for discharging droplets can be arranged to print the printing area in one pass,
The head unit is provided so as to be movable between an image forming position corresponding to a printing area and a maintenance position for performing maintenance and recovery.
First droplet detecting means for detecting droplets ejected from the head unit at the image forming position during printing;
Second droplet detection means for detecting droplets discharged when the head unit is in a maintenance position;
Means for detecting droplets discharged by the second droplet detection means before moving the head unit from the maintenance position to the image forming position, and detecting the discharge state of the head unit;
It was set as the structure equipped with.

  Here, the plurality of head units include at least one more head unit than the number necessary for printing the printing area in one pass, and the head unit at the image forming position and the head at the maintenance position. It can be configured to perform printing while changing units.

  The head units can have the same configuration.

  The plurality of head units may be arranged to be movable in a direction orthogonal to the paper transport direction.

  According to the image forming apparatus of the present invention, the first liquid droplet detecting unit that detects the liquid droplets discharged during printing from the head unit at the image forming position, and the liquid droplets discharged when the head unit is at the maintenance position. A second liquid droplet detecting means for detecting a liquid droplet to be detected, and a liquid droplet discharged by the second liquid droplet detecting means before the head unit is moved from the maintenance position to the image forming position. The head to be replaced can be detected by detecting the discharge of the head unit not related to the printing and checking the discharge state of the head not related to the discharge while performing the printing discharge detection during the printing. Since the discharge state of the unit is guaranteed, the reliability with respect to discharge failure is improved, and the head can be used efficiently.

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an example of an ink jet recording apparatus as an image forming apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a schematic explanatory view of the ink jet recording apparatus.
The ink jet recording apparatus 1 includes a head unit 11 in which heads for ejecting ink are integrated, a maintenance unit (not shown) that performs head maintenance (maintenance recovery) corresponding to each head unit 11, black ( K), cyan (C), magenta (M), and yellow (Y) ink cartridges 7K, 7C, 7M, and 7Y that supply ink of each color (referred to simply as “ink cartridge 7” when colors are not distinguished). The same applies to the members.) Sub-ink tanks 8K, 8C, 8M, and 8Y that partially store ink from the ink cartridge 7 and supply the ink to the head of the head unit 11 at an appropriate pressure are provided.

  Further, the conveyance belt 13 that sucks and conveys the paper 14, the conveyance rollers 19 and 21 that support the conveyance belt 13, the tension roller 15 that controls the conveyance belt 13 to maintain an appropriate tension, and the conveyance belt 13 have an appropriate flatness. A transport mechanism comprising a platen 24 for maintaining, a charging roller 18 for applying electrostatic charge to attract the paper 14, a separation claw 20 for separating the paper 14 from the transport belt 13, and a paper discharge roller for transporting paper. 16, a sheet discharge roller 17 for pressing the sheet, a sheet discharge mechanism including a sheet discharge tray 4 for storing the discharged sheet 14, one sheet from the sheet feed tray 3 for storing the sheet 14 to be printed, and the sheet feed tray 13. A paper feed roller 12 that feeds the paper 14 one by one, a counter roller 23 that reliably attracts the fed paper 14 to the charged transport belt 13, and a manual feed And a paper feed mechanism comprising a manual feed tray 5 to be used when the paper feed.

  Further, a waste liquid tank 9 for collecting waste liquid discharged after maintenance and an operation panel 6 capable of operating the apparatus and displaying the apparatus state are also provided.

  The nozzle rows of each head unit 11 are arranged so as to be orthogonal to the conveyance direction of the paper 14, and form a nozzle row longer than the recording area. The paper 14 is separated from the paper feed tray 13 one by one by the paper feed roller 12 and fed, and is fixed on the transport belt 13 by being in close contact with the transport belt 13 by the counter roller 23. By ejecting droplets onto the sheet 14 when passing below, the sheet can be patterned with droplets at high speed, separated from the transport belt 13 by the separation claw 20, and discharged from the discharge roller 16 and the sheet discharge. The recorded matter is discharged to the discharge tray 4 supported by the rollers 17.

Here, an example of the head unit 11 constituting the recording head of the image forming apparatus will be described with reference to FIGS. 2 is an explanatory plan view when the head unit is viewed from the nozzle surface side, and FIG. 3 is an enlarged plan view when one head constituting the head unit is viewed from the nozzle surface side.
In the head unit 11, six liquid ejection heads 101 </ b> A to 101 </ b> F are arranged on a head support member 100 in two rows in a staggered manner in the arrangement direction of nozzles 102 formed on the nozzle surface 104 (direction along the nozzle row 103). The parts are arranged in an overlapping manner. One head 101 has a nozzle surface 104 in which nozzle rows 103 in which a plurality of nozzles 102 for discharging droplets are arranged side by side are arranged in two rows in a staggered manner. Then, between the head support member 100 and the liquid discharge head 101, as shown in FIG. 4, a filler 105 is filled and sealed, and a gap from the nozzle surface 104 side is eliminated.

  Further, the head support member 100 and the nozzle surface 104 are fixed so as to be located on substantially the same plane. That is, if there is a step between the nozzle surface 104 and the head support member 100 that is the head outer peripheral member at the time of wiping, the wiper blade 140 is caught by the step and cannot contact the nozzle surface 104 with an equal force, and wiping was performed. Sometimes left behind. In addition, since a blind spot that cannot be contacted by the wiper blade is generated at the level difference, ink is easily collected, and the accumulated ink falls on the paper 14 during printing, thereby degrading the image quality. Further, if there is a level difference, the pressure applied to the wiper blade locally increases, so that friction between the wiper blade and the contact portion increases, and wear of the nozzle face contact end surface of the wiper blade is caused in a durable manner.

Next, another example of the head unit 11 constituting the recording head will be described with reference to FIGS. 5 is an explanatory plan view of the head unit as seen from the nozzle surface side. FIG. 6 is an enlarged plan view of one liquid discharge head constituting the head unit as seen from the nozzle surface side.
The head unit 11 is configured by arranging six heads 111 </ b> A to 111 </ b> F on a head support member 100 so as to partially overlap each other in the nozzle arrangement direction (direction along the nozzle row) in a two-row zigzag pattern. One liquid discharge head 111 has a nozzle surface 104 on which a plurality of nozzle rows 113a to 113f in which a plurality of nozzles 112 for discharging droplets are arranged in a staggered manner are arranged. And between the head support member 100 and the head 111, the filler is filled and sealed in the same manner as described above to eliminate the gap from the nozzle surface 104 side.

  When this head unit 11 is used, it is possible to increase the number of colors without increasing the size of the apparatus by changing the color of ink for each of the nozzle rows 113a to 113f. In addition, when the same color ink is used, a head that cannot discharge all nozzles at the same time can discharge with multiple nozzle rows, so the same ink can be discharged without thinning out and the printing speed is improved. Can be made. When multi-coloring is performed with the head unit 11 having this configuration, the landing position accuracy of the adjacent nozzle row is the highest, so dark ink that is easy to detect the landing position is placed on the center side of the head unit 11, and light ink is placed on the head. It is preferable to arrange on the outer edge side of the unit 11.

  In this image forming apparatus configured as described above, the nozzle rows of the head units 11 are arranged so as to be orthogonal to the conveyance direction of the paper 14, and the plurality of units 11 are arranged so as to be longer than the recording area. The nozzle row is formed.

An outline of the arrangement of the head units 11 will be described with reference to FIGS.
Here, the head units 11A to 11D are arranged at image forming positions, and the areas 26A to 26D that can be ejected from the arranged head units 11A to 11D are located so as to be the entire surface of the sheet. Further, the head unit 11E is disposed at a maintenance position for performing maintenance and recovery. The head unit 11E can move to the same place relative to the print position of the paper and the head unit 11 at the image forming position, thereby enabling printing to be performed alternately.

  In addition, maintenance units 10A to 10D are arranged corresponding to the head units 11A to 11D at the maintenance position, and a maintenance unit 10E is arranged corresponding to the head unit 11E.

  Each of the head units 11A to 11E is movable in a direction perpendicular to the paper transport direction to the position of the maintenance units 10A to 10E which are maintenance and recovery means for performing discharge maintenance or recovery operation. Is configured so as to be freely movable between the areas 26A to 26D that can be discharged from the maintenance units 10A to 10E.

  Each head unit 11 can move to the maintenance position and perform maintenance / recovery, and can perform maintenance / recovery operation outside the transport path. Therefore, maintenance or recovery (hereinafter referred to as “maintenance” or “ It is also called “maintenance and recovery” but is used in the same meaning.). The maintenance operation is an operation for continuously discharging, for example, an empty discharge operation for discharging ink to a non-recording portion, and the recovery operation is a head surface for discharging the non-discharge portion of the head again. It means operations such as suction to discharge ink, pressure supply of ink from a supply port, discharge of ink from the head, and then wiping off excess ink adhering to the head.

  As shown in FIG. 8, the maintenance unit 10 corresponding to the head unit 11 includes a cap 149 having a cap nip portion 150 for capping the nozzle surface, an empty discharge receiver 141 for discharging liquid droplets that do not contribute to image formation, and a nozzle surface. A wiper member 140, a frame for moving up and down, a driving source (not shown), a cap suction path, and a pump for the same. The maintenance operation is performed in the vicinity of the maintenance unit 10. The maintenance operation is composed of idle ejection, suction operation, and wiping, but is not limited to this. For example, instead of suction by a cap, ink is pressurized and supplied from an ink supply port, and the ink is discharged from the head. You may do it.

Such movement of the head unit 11 is performed in the same manner as in the serial type image forming apparatus. Therefore, the movement of the head unit will be described with reference to FIGS.
The head unit 11 is provided with an encoder reading sensor 146 and a belt clip 147, and the encoder reading sensor 146 passes through a gap between the linear encoder 142 and the head unit 11 so that the linear encoder (encoder scale) 142 can be detected. .

  The head unit 11 is supported by a guide lot 25, and a head unit moving belt 143 stretched between a head unit moving motor 144 and a tension roller 145 is held by a belt clip 147 provided on the head unit 11. The movement is transmitted to the head unit 11.

  Further, the ink supply tube 148 that supplies ink to the head unit 11 can be bent according to the movement of the head unit 11, and has a low fluid resistance that is sufficient to supply ink even with the maximum consumption of ink. The cross-sectional area is obtained.

  In this way, by configuring the head unit with the same type, it is possible to equalize the image allocation and maintenance work time after replacement, resistance to decap time, heat capacity of the head unit, etc., and control is simplified Therefore, the reliability can be improved by reducing the defect of the control software. In addition, when the head unit fails or is damaged, it is only necessary to prepare the same parts, and it is difficult to make a mistake in replacement, thereby improving maintainability.

Next, an outline of the control unit of the ink jet apparatus will be described with reference to FIG. This figure is an overall block diagram of the control unit.
The control unit 300 includes a CPU 301 that controls the entire apparatus, a program executed by the CPU 301, a value of light reception sensitivity change of predetermined droplet discharge detection used in the present invention, a sensitivity threshold that is regarded as droplet detection, drive waveform data, ROM 302 for storing other fixed data, RAM 303 for temporarily storing image data and the like, non-volatile memory (NVRAM) 304 for holding data even while the apparatus is powered off, and various signals for image data An ASIC 305 that processes image processing for processing, rearrangement, and the like, and other input / output signals for controlling the entire apparatus.

  The control unit 300 also includes an I / F 306 for transmitting and receiving data and signals to and from the host side, and a head drive control unit 307 that generates a drive waveform for driving and controlling the pressure generating means of the recording head 154. , A paper conveyance motor drive unit 308 for driving the paper conveyance motor 309, a head unit movement motor drive unit 310 for driving the head unit (carriage) movement motor 311, and a drive for the maintenance unit movement motor 313. Maintenance unit movement motor drive control unit 312; ink path valve control unit 314 for controlling opening and closing of electromagnetic valve 315 in the ink path; liquid feeding suction motor drive control unit for controlling driving of cap suction motor 317 and ink supply motor 318 316 and an output for outputting a detection signal corresponding to the moving amount and moving speed of the conveyor belt 113. I / O 322 for inputting a detection signal from a sensor 323 for detecting a coder, environmental temperature and environmental humidity (whichever is acceptable), an ink amount detection signal for the sub ink tank, and various detection sensors (not shown). Etc. An operation / display unit 106 for inputting and displaying information necessary for the apparatus is connected to the control unit 300.

  The control unit 300 receives print data and the like from the host side such as an information processing device such as a personal computer, an image reading device such as an image scanner, and an imaging device such as a digital camera, via the cable or the network, via the I / F 316.

  Then, the CPU 301 reads and analyzes the print data in the reception buffer included in the I / F 306, performs necessary image processing, data rearrangement processing, and the like in the ASIC 305, for one page of the head width of the recording head 154. Is sent to the head drive controller 307 in synchronization with the clock signal. The dot pattern data for image output may be generated by storing font data in the ROM 302, for example, or the image data is rasterized into raster data by a host-side printer driver and transferred to this apparatus. Anyway.

  The head control unit 307 transfers the head drive information to the head drive control unit 321, and the head drive control unit 321 is based on image data (dot pattern data) corresponding to one page of the head unit 11 input in units of pages. Then, each head 101 of the head unit 11 is driven by selectively applying to the pressure generating means of each head 101 of the head unit 11 (or the head 111. The same applies hereinafter).

  The head control unit 307 also transfers a droplet detection command issued from the CPU 301 to the droplet detection control unit 320. The droplet detection control unit 320 is a droplet detection unit according to the present invention described later according to the timing of the command. A droplet detection device 324 is controlled.

  Although details will be described later, the droplet detection device 324 indicates the discharge state of the droplets from each head 101 of the head unit 11 through the light emitting unit 325 that is a light emitting unit, the light receiving unit 326 that is a light receiving unit, and the optical axis deflecting device 327. Detection is performed, and detection data obtained based on the detection result is transferred to the CPU 301 via the droplet detection control unit 320.

  The liquid discharge head used in the image forming apparatus to which the present invention is applied includes a piezoelectric head that discharges droplets by applying a voltage to the electrostrictive element and deforming the electrostrictive element, and an electric current to the electrothermal conversion element. A thermal type head that generates heat by flowing and foams liquid by generating heat, and discharges droplets by electrostatic force between the diaphragm and electrodes, and mechanically drops droplets by the restoring force of the diaphragm. An electrostatic head for discharging can be used, and the actuator means (pressure generating means) for discharging droplets is not limited. In the piezoelectric head, by adjusting the driving waveform for driving the piezoelectric element, it is possible to eject droplets of various sizes, which is advantageous for forming an image with good gradation. On the other hand, the thermal type head is easy to highly integrate nozzles and is suitable for the production of a multi-nozzle head. Therefore, it is advantageous for printing an image with high resolution at a high speed.

  Further, the liquid discharge head may be an edge shooter method in which the shape from the liquid flow path to the discharge port (nozzle) is linear, or a side shooter method in which the liquid flow channel direction and the discharge port direction are different. There may be.

  As the coloring material used in the ink, any of a pigment and a dye can be used, and they can be used in combination. There is no particular limitation on the water-dispersible colorant used in the ink, but it can be added to water without a dispersant due to the treatment that at least one hydrophilic group is bonded to the pigment surface directly or through other atomic groups. A pigment emulsion that has become dispersible, or a polymer emulsion in which resin fine particles contain a water-insoluble or hardly soluble colorant, or a surfactant or a water-soluble polymer compound having an average molecular weight of 50,000 or less are used alone or in combination. It is preferable to use the water-dispersed colorant of the pigment which has been stabilized by dispersion alone or in combination.

  Although there is no limitation in particular as a pigment kind to be used, an organic pigment and an inorganic pigment can be used, and an organic pigment is used suitably especially in terms of specific gravity. Moreover, you may use these pigments in mixture of multiple types. The particle diameter of these pigments is preferably 0.01 to 0.30 [mu] m. If the particle diameter is 0.01 [mu] m or less, the light resistance and feathering are deteriorated because the particle diameter approaches that of the dye. On the other hand, if it is 0.30 μm or more, clogging of the discharge port or clogging with a filter in the apparatus occurs, and discharge stability cannot be obtained.

  Such water-dispersible colorants have water resistance, light resistance, and gas resistance because the colorant molecules are in an aggregated state (including crystal state) or coexist with resin molecules and do not exist as single molecules. It is excellent, and when such a colorant is used, image storage stability can be improved. In particular, pigments that are dispersible in water without a dispersant due to treatment that at least one hydrophilic group is bonded directly or via other atomic groups to the pigment surface, or water insoluble in fine resin particles Alternatively, when a polymer emulsion containing a hardly soluble coloring material is used, the ink viscosity with respect to the colorant solid content can be kept low, so that a large amount of water-dispersible resin or wetting material can be added.

  The resin used in the ink is not particularly limited, but the water-dispersible resin preferably has a pH of 6 to 11 and more preferably a pH of 7 to 9 because of miscibility with the water-dispersed colorant. As a characteristic of the dispersible resin, the smaller the average particle size, the higher the viscosity. The average particle size of the water-dispersible resin is preferably 50 nm or more so as not to have an excessively high viscosity.

  Further, since the ink flow path and nozzle opening of the liquid discharge head are small, it is known that the discharge performance is deteriorated when particles having a large particle diameter are present in the ink. The average particle diameter is preferably 500 nm or less, and particularly preferably 150 nm or less, in order not to inhibit the ink ejection properties. The water-dispersible resin preferably has a function of fixing the water-dispersed colorant on the paper surface. In order to improve the fixability, the minimum film-forming temperature (MFT) is preferably 20 ° C. or lower. However, when the glass transition point is −40 ° C. or lower, the resin film becomes more viscous and the printed matter is tacky. Therefore, a water dispersible resin having a glass transition point of −30 ° C. or higher is preferable.

  In order to make the ink have desired physical properties or to prevent clogging of the nozzles of the recording head due to drying, it is preferable to use a water-soluble organic solvent in addition to the coloring material. The water-soluble organic solvent includes a wetting agent and a penetrating agent. The wetting agent is added for the purpose of preventing clogging of the nozzles of the recording head due to drying. These solvents are used alone or in combination with water.

  The penetrating agent is added for the purpose of improving the wettability between the ink and the recording material (paper) and adjusting the penetrating speed. Examples of penetrants include polyoxyethylene alkylphenyl ether surfactants, acetylene glycol surfactants, fluorine surfactants, silicon surfactants, polyoxyethylene alkyl ether surfactants and polyoxyethylene polyoxy Propylene alkyl ether surfactants can be exemplified, and these compounds can reduce the surface tension of the liquid, so that the wettability can be improved and the penetration rate can be increased.

  The ink can contain antiseptic and antifungal agents. By containing the antiseptic / antifungal agent, the growth of bacteria can be suppressed, and the storage stability and the image quality stability can be improved. Further, the ink can contain a rust inhibitor. By containing a rust preventive agent, a coating can be formed on the metal surface in contact with the liquid, such as a head, and corrosion can be prevented. The ink can contain an antioxidant. By containing an antioxidant, even when radical species that cause corrosion are generated, the antioxidant can be prevented by eliminating the radical species.

  The ink can contain a pH adjuster. The pH of the ink is preferably 3 to 11, and more preferably 6 to 10 from the viewpoint of preventing corrosion of the metal member in contact with the ink. The pH adjuster can adjust the pH of the recording liquid of the present invention to a preferable range.

The surface tension of the ink is preferably 20 to 60 mN / m, and more preferably 30 to 50 mN / m from the viewpoint of achieving both wettability with the recording material and droplet formation.
The viscosity of the ink is preferably 1.0 to 20.0 mPa · s, and more preferably 2.0 to 10.0 mPa · s from the viewpoint of ejection stability.

Next, a maintenance operation in this ink jet recording apparatus will be described with reference to FIG.
In the maintenance operation in this case, the head unit 11 first moves to a capping position (hereinafter abbreviated as “home position: HP”), and the cap 149 is raised to perform capping. The head unit 11 waiting at the maintenance position is also in the capping state (FIG. 12A).

  When performing maintenance, the ink is discharged from the head unit 11 in the capping state (FIG. 12A) (FIG. 12B). As a discharging method, any one of a method of increasing the ink pressure in the head unit 11 and discharging from the nozzle, a method of decreasing the pressure in the cap 149 and sucking and discharging the ink in the head unit 11, or a combination of the two methods can be used. It may be used.

  After discharging the ink of the head unit 11 into the cap 149, the cap 149 is lowered and separated from the head unit 11, and the wiper member 140 is raised to the extent that it contacts the nozzle surface of the head unit 11 (FIG. 12C). .

  Then, while moving the head unit 11 in the direction of the image forming position, the ink 151 attached to the nozzle surface is wiped by contacting the wiper member 140 (FIG. 12D), and the head unit 11 is moved from the maintenance position to the image forming position. It moves and stops (FIG. 12 (e)). Thereafter, while the wiper member 140 is lowered, the ink adhering to the surface of the wiper member 141 is scraped off by the idle ejection receiver 141 to clean the wiper member 140 (FIG. 12F).

  The head unit 11 performs idle discharge 152 on the empty discharge receiver 141 while moving to the maintenance position (FIG. 12 (g)). After detecting the discharge by the droplet discharge detection 154 (FIG. 13 described later), the head unit 11 is normal. Then, it returns to the maintenance position and stops (FIG. 12 (h)). If there is a missing nozzle, the maintenance operation (FIG. 12 (a)) is performed again.

  If the head unit 11 does not immediately move to the image forming position, the cap 149 is raised as it is to enter the capping state (FIG. 12A). When moving to the image forming position, the image forming position is moved without capping as it is.

Next, droplet discharge detection in this ink jet recording apparatus will be described with reference to FIGS.
This ink jet recording apparatus has two droplet discharge detection systems, one is a first droplet detection unit 401 that detects droplet discharge during printing, and the other is droplet discharge detection before maintenance or printing. This is a second droplet discharge detection means 402 that performs the above.
The first droplet detection unit 401 that detects droplets during printing discharges the light emitted from the light emitting / receiving unit 157 until it is reflected by the reflecting mirror 158 and returns to the light emitting / receiving unit 157 again. The detection optical path 153 is blocked by the liquid droplets ejected from the head unit 11, and the light is absorbed, so that the light receiving sensitivity is lower than when there is no liquid droplet, thereby detecting the liquid droplet.

The first droplet detecting means 401 for detecting the droplet during printing will be described with reference to a perspective explanatory view shown in FIG. 14 and a schematic explanatory view shown in FIG.
The optical axis for detecting the droplet is emitted from the laser diode 161, the beam diameter is determined by the collimator lens 160 through the beam splitter 159, and enters the polygon mirror 165 as parallel light. The laser light refracted by the polygon mirror 165 is incident on the light emitting / receiving mirror 163 via the fθ lens 164, and the optical axis is bent so as to pass through the detection region 166. The light is reflected by the reflection mirror 158 at the tip of the detection region 166 and returns in the reverse order on the same optical path. The optical axis is changed by the beam splitter 159, and the laser light reaches the photodiode 162. Since the polygon mirror 165 moves, the optical axis is slightly different between the forward path and the return path, and the optical path from the polygon mirror 165 on the return path to the photodiode 162 is not parallel to the forward path. Therefore, the detection efficiency can be improved by using a correction means for optical path correction, a method of providing a condenser lens in front of the photodiode 162, or the like.

  In addition, when it hits a droplet in the detection region, the laser light is scattered and absorbed at the portion hitting the droplet, and further absorbed and scattered in the return path, so that the amount of light reaching the photodiode 162 is reduced. . Therefore, the S / N ratio is increased and the sensitivity is improved.

  Next, the second droplet detection unit 402 that performs droplet discharge detection before maintenance or printing has the discharge detection optical path 154 until the light emitted from the light emitting unit 155 enters the light receiving unit 156. The liquid droplets are detected by the light receiving sensitivity being lower than when there are no liquid droplets by being blocked by the liquid droplets discharged from 11 and absorbing light.

The second droplet detecting means 402 for performing the maintenance and droplet detection before printing will be described with reference to a perspective explanatory view shown in FIG. 16 and a schematic explanatory view shown in FIG.
The light emitting unit 155 emits the laser light emitted from the laser diode 261 into parallel light having an appropriate width by the collimator lens 260. The light that passes above the empty discharge receivers 141 </ b> E to 141 </ b> A, which are the detection region 266, enters the light receiving unit 156, and is collected by the condenser lens 267, and enters the photodiode 262.

  When it hits a droplet in the detection region 266, the laser light is scattered and absorbed at the portion hitting the droplet, and detection is possible. In addition, since the discharge inspection can be performed at a position where the empty discharge receiver 141 is located below, it is possible to discharge a plurality of droplets from the same nozzle and detect a discharge variation. The ink in the meniscus area at the nozzle (orifice) is drying and increasing in viscosity, but it is necessary to check whether it is completely normal by performing discharge detection many times until normal discharge is achieved. Can do. In addition, discharge detection can be performed during idle discharge, and maintenance time can be shortened.

Next, printing control and maintenance control according to the present invention will be described with reference to the flowcharts shown in FIGS.
Regarding print control, referring to FIG. 18, the print preparation of the head unit is first executed. In the head unit printing preparation, as shown in FIG. 19, priority is given to printing for the head units 11 (11 </ b> A to 11 </ b> E) existing at the maintenance position, and maintenance liquids are assigned according to the priority order of the head units 11. Confirm droplet discharge by droplet detection. If there is a defective nozzle, the recovery of the head unit 11 is reserved, and the order is changed so that the printing priority of the head unit 11 becomes the lowest. When there is no ejection failure, if the priority is the printing range, the image forming position is moved. This operation is repeated until all the image forming positions are filled with the head unit 11 to prepare for printing.

  Next, returning to FIG. 18, the print image is raster-developed, and a print surface empty discharge pattern is applied to the raster image.

  After that, raster-processed main data for image formation (data to be printed on the center portion 133 in FIG. 23) is formed, and a blank discharge pattern for printing hollow discharge is formed in the left and right margins (both ends 132 in FIG. 23). Form and join to main data. The empty ejection data is formed by applying a blue noise mask or the like so that the adjacent pixels are not ejected so that the ejection pixels are not conspicuous and the ejection droplet row does not form a periodic pattern. Similarly, upper and lower margin portions (upper end portion 130 and lower end portion 131 in FIG. 23) are formed and joined to main data. Since this data confirms the ejection, it is preferable to process the ejection image so as to refrain from ejection of other nozzles, which is an impediment to ejection detection of the target nozzle. In parallel with these operations, paper is fed to the printing unit (printing area for the head unit 11).

  When the image forming data can be generated, while the paper is fed, printing is performed with an empty ejection pattern in the upper margin, and the ejection state of the liquid droplet is detected by the printing liquid drop detection device to determine the presence or absence of a defective ejection nozzle. .

  When a defective nozzle is detected, as shown in FIG. 20, the head unit 11 including the target nozzle is identified, and the head unit 11 having the defective nozzle and the head unit 11 in the standby state at the maintenance position The replacement operation is performed, and the image is printed again when the replacement of the head unit 11 is completed.

  After outputting the print image, the printer waits for a predetermined time at the image forming position. When data is input, print processing from raster development is performed again. If no additional printed image is input, the head unit shown in FIG. 21 is stored, and the printing process is terminated.

  Here, as shown in FIG. 21, the head unit storage operation is performed by moving the head unit 11 to the home position HP based on the printing priority order of the head unit 11 and discharging the idle discharge to the idle discharge receptacle during the movement. While performing, discharge detection is performed by a droplet detection device for maintenance. When there is a discharge failure, the head recovery operation is performed. When there is no discharge failure, the head moves to the home position HP as it is, and capping is performed. This is performed for the head units 11 at all image forming positions, and the process ends when all the head units 11 are capped.

  Further, as shown in FIG. 20, in the replacement operation of the head unit, the priority order of the head unit 11 to be replaced is made the lowest, and the recovery operation of the head unit 11 is reserved. The head unit 11 having the highest priority among the head units 11 waiting at the maintenance position is subjected to droplet detection at the maintenance position using the second droplet detection unit 402, and the ejection state of the head unit 11 is detected. Is detected (confirmed) to determine whether there is a discharge failure. If there is a discharge failure, if there is another standby head unit 11, a recovery operation of the head unit 11 is reserved and the head unit 11 is reserved. Change the priority of to the lowest. If there is no other standby head, the recovery operation of the head unit 11 is performed.

  If there is no ejection failure of the standby head, the standby head unit 11 is moved to a position corresponding to the printing position of the replacement head unit 11 and printing is performed instead of the replacement head unit 11. When printing starts instead, the exchange head unit 11 moves to the home position HP, and the exchange is completed.

  When the recovery operation reservation is made, the recovery operation is performed as shown in FIG. 22 from the head unit 11 with the higher print priority that is reserved for the recovery operation while there is no replacement work of the head unit 11 or the like.

  As in the head maintenance described above, this recovery operation is performed by capping the head (the head of the head unit 11), discharging ink from the head, separating the head and the cap 149, and then sucking the cap 149. Wiping is performed by the wiper member 140, and idle ejection is performed on the idle ejection receiver 141. In addition to performing idle ejection, a defective nozzle is detected, and if there is a defective ejection, the maintenance operation is performed again. When there is no ejection failure nozzle, capping is performed when there is no printing operation immediately after.

Next, another embodiment of the present invention will be described with reference to FIG. FIG. 3 is a flowchart showing the printing process in the embodiment.
In this embodiment, the head unit is replaced according to the elapsed time in an uncapped state (decap state).

  When printing is performed, the head unit 11 is prepared for printing, the cap 149 is removed, the head unit 11 is moved to the printing position, and measurement of the elapsed time (decap time T) in the decap state is started.

  The print image is raster-developed, and a print surface empty discharge pattern is added to the raster data. In parallel, paper feeding is performed, and ejection is confirmed while printing for one page. If there is a discharge failure, the recorded matter is discharged and the head unit 11 is replaced. If there is no ejection failure, it is evaluated whether the decap time T is less than the specified value. If the decap time T is longer than the specified value, the formed paper is discharged while the head unit 11 is replaced. The subsequent processing is the same as the printing processing (FIG. 18) of the above embodiment.

  Unlike nozzle omission, exceeding the specified decap time does not cause a problem in image formation. However, since the possibility of drying of the meniscus of the orifice (nozzle) and the mixing of paper dust is increased, regular maintenance is performed by setting specified values according to the ink physical properties, usage environment, and head characteristics. Reliability can be increased.

Here, when the head unit is moved, the movement can be controlled based on the printing order of the head unit. This printing order will be described with reference to FIG.
A: Movement for printing When the head unit is moved, the head unit is prepared for printing as described in the flowchart of FIG. In this print preparation, as shown in FIG. 25A, the print unit is assigned a print priority in the standby state at the maintenance position. This priority order is determined based on the usage time of the head unit used so far, the ink discharge amount, the head temperature, and the like. When moving to the image forming position, up to the required number of head units is selected from the higher priority order and moved to the image forming position to perform printing. When printing is completed, the head unit is stored as described with reference to the flowchart of FIG. 21, and capping is performed while moving from the head unit having a higher priority to the maintenance position.

B: Replacement of ejection failure In replacing the ejection failure of the head unit, a head unit including a nozzle with ejection failure is identified (No. 2 in FIG. 25B). As described with reference to the flowchart of FIG. 20, the head unit with the highest priority (No. 4 in the example of FIG. 25B) that has been waiting at the home position HP is No. 4. The head unit 2 moves to a location corresponding to the image forming position. After moving, no. No. 2 head unit priority is changed to the lowest priority. Head units with a rank of 2 or less perform a process of raising the rank. No. The second head unit is moved to the maintenance position, and the replacement is completed.

C: Replacement by time When replacing according to the decap time of the head unit, the head unit having the longest decap time is specified. When A and B are used, the decap time is long, that is, not replaced, that is, the head unit having the highest rank (No. 1 in FIG. 24C). As described in the flowchart shown in FIG. 20, the head unit having the highest priority (No. 4 in FIG. 25C) that has been waiting at the home position HP is No. 4. It moves to a location corresponding to the image forming position of one head unit. After moving, no. No. 1 head unit priority is changed to the lowest priority. The head units with a rank of 1 or less perform a process of raising the rank. No. The one head unit is moved to the maintenance position, and the replacement is completed.

  Thus, by registering the priority order as a parameter as a value for managing the head unit and using it for control, the head unit can be efficiently circulated between printing and maintenance. In addition, when performing different operations at the same time, it is possible to work efficiently by providing a reservation process.

  In the image forming apparatus of the present invention, since maintenance operation can be executed during printing and the discharge performance of the replacement head is confirmed, the productivity can be improved and the reliability can be improved. Further, since the head units can be exchanged with each other, the load on the head can be equalized and the durability can be improved. Further, by using the same configuration (same type) as the head unit, it is possible to reduce the number of replacement parts and improve the maintainability.

Next, another example of a configuration for moving the head unit will be described with reference to a perspective explanatory view shown in FIG.
In this example, the head unit 11 moves in the vertical direction with respect to the printing surface, and then moves in the horizontal direction to move toward the cap 149 side of the maintenance unit 10. When such a configuration is used, the maintenance position can exist in a direction perpendicular to the image forming position, and the installation area of the image forming apparatus can be reduced.

Next, another example of the droplet detection device (means) will be described with reference to a plan view of FIG.
The image forming apparatus according to the present invention has two droplet discharge detection systems, one is a first droplet detection unit 401 that detects droplet discharge during printing, and the other is a liquid before maintenance or printing. A second droplet detection unit 402 that detects droplet discharge.
During the printing, the droplet detecting means 401 blocks the discharge detection optical path 153 by the droplets ejected from the head unit 11 and absorbs the light until the light emitted from the light emitting portion 172 enters the light receiving portion 173. Therefore, the light receiving sensitivity is lower than when there is no liquid droplet, thereby detecting the liquid droplet.

  The light emitting portion 172 is fixed to the light emitting portion carriage 171 and can reciprocate in the same direction as the head unit 11 along the light emitting side guide rod 169. The light receiving portion 173 is fixed to the light receiving portion carriage 170 and can reciprocate in the same direction as the head unit 11 along the light receiving side guide rod 168.

  As with the head unit 11, both carriages 170 and 171 can detect a movement count by a linear encoder and convert it into position information, and can move to a desired position by transmitting a driving force from a motor via a moving belt. it can. The light-emitting part carriage 170 and the light-receiving part carriage 171 are moved oppositely and equally so that the light-receiving part 173 always exists on the ejection detection optical path 153.

  The optical path of this droplet detection will be described with reference to FIG. 28. The laser light emitted from the laser diode 471 in the light emitting portion 172 is emitted as parallel light having an appropriate width by the collimator lens 470. Light that passes under the head unit, which is the detection region 153, enters the light receiving portion 173, and is collected by the condenser lens 467, enters the photodiode 462. When it hits a droplet in the detection region 153, the laser light is scattered and absorbed at the portion where it hits the droplet, and detection is possible.

  The second droplet detection means 402 that performs droplet discharge detection before maintenance or printing is the same as that described in the above embodiment, and thus the description thereof is omitted.

  In the above description, the droplet detection device before maintenance or printing is described as an optical detection device. However, a capacitance sensitive type may be used, and the capacitance sensitive type has no optical path limitation. Therefore, there is an advantage of increasing the degree of freedom of arrangement layout.

  In the above embodiment, the present invention has been described with reference to an example in which the present invention is applied to an image forming apparatus having a printer configuration. However, the present invention is not limited to this. For example, the present invention may be applied to an image forming apparatus such as a printer / fax / copier multifunction machine. it can. Further, the present invention can be applied to an image forming apparatus using a liquid other than the narrowly defined ink, a fixing processing liquid, or the like.

1 is a schematic side view illustrating an example of an image forming apparatus according to the present invention. It is the plane explanatory view seen from the nozzle side which shows an example of the head unit of the device. It is the plane explanatory view seen from the nozzle side which shows the head of the head unit. FIG. 3 is an enlarged explanatory view of a main part when viewed from a nozzle side showing a head periphery portion of the head unit. It is plane explanatory drawing seen from the nozzle side which shows the other example of the head unit of the same apparatus. It is the plane explanatory view seen from the nozzle side which shows the head of the head unit. FIG. 5 is an explanatory plan view for explaining the arrangement of head units. It is front explanatory drawing similarly. It is front explanatory drawing used for description of a movement of a head unit. It is a plane explanatory drawing similarly. It is block explanatory drawing which shows the outline | summary of the control part of the apparatus. It is principal part front explanatory drawing used for description of the maintenance operation | movement of the apparatus. It is plane explanatory drawing with which it uses for description of a droplet detection apparatus. FIG. 3 is a perspective explanatory view for explaining a droplet detecting device during printing. It is a schematic explanatory drawing similarly. FIG. 3 is a perspective explanatory view for explaining a maintenance / pre-printing droplet detection device. It is a schematic explanatory drawing similarly. It is a flowchart with which it uses for description of a process of printing control and maintenance control. It is a flowchart with which it uses for description of the print preparation process of the head unit of FIG. It is a flowchart with which it uses for description of the head unit replacement | exchange process of FIG. It is a flowchart with which it uses for description of the preservation | save operation | work process of the head unit of FIG. It is a flowchart with which it uses for description of the nozzle recovery process of FIG. It is explanatory drawing with which it uses for description of the printing of the raster image of FIG. It is a flowchart with which it uses for description of the printing process in other embodiment of this invention. It is explanatory drawing with which it uses for description of the specific example of replacement | exchange of a head unit. FIG. 10 is a perspective explanatory view for explaining another example of the moving configuration of the head unit. It is a plane explanatory view used for description of another example of the droplet detection means. It is explanatory drawing with which it uses for description of the optical path of a 1st droplet detection means similarly.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Inkjet apparatus 3 ... Paper feed tray 4 ... Paper discharge tray 6 ... Operation panel 7 ... Ink cartridge 8 ... Sub ink tank 10 ... Maintenance unit 11 ... Head unit 13 ... Conveyor belt 14 ... Paper 26 ... Print area by head unit 140 ... Wiper member 141 ... Empty discharge receptacle 149 ... Cap 153 ... Discharge detection optical path 154 ... Discharge detection optical path 2
155... Light emitting part 156. Light receiving part 157. Light emitting / light receiving part 172. Light emitting part 173. Light receiving part 320 .. Liquid drop detection control part 321... Head drive control part 324 ... Liquid droplet detection device 401. ... Second droplet detection means

Claims (4)

A plurality of head units having a head for discharging droplets can be arranged to print the printing area in one pass,
The head unit is provided so as to be movable between an image forming position corresponding to a printing area and a maintenance position for performing maintenance and recovery.
First droplet detecting means for detecting droplets ejected from the head unit at the image forming position during printing;
Second droplet detection means for detecting droplets discharged when the head unit is in a maintenance position;
Means for detecting droplets discharged by the second droplet detection means before moving the head unit from the maintenance position to the image forming position, and detecting the discharge state of the head unit;
An image forming apparatus comprising:   2. The image forming apparatus according to claim 1, wherein the plurality of head units include at least one more head unit than the number required for printing the printing area in one pass, and are in the image forming position. An image forming apparatus for performing printing while replacing a head unit and a head unit at a maintenance position.   The image forming apparatus according to claim 1, wherein the head units have the same configuration.   4. The image forming apparatus according to claim 1, wherein the plurality of head units are arranged so as to be movable in a direction orthogonal to a paper transport direction. 5.

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