JP2011126131A - Apparatus and method for forming image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for forming an image, in each of which the throughput when many pieces of recording media are printed at a high speed is restrained from being deteriorated and the contact of an inkjet head with the recording medium is prevented. <P>SOLUTION: The apparatus for forming the image includes: a conveyance part for conveying the recording medium to the position which is just under the inkjet head including a nozzle and is opposed to the inkjet head; a paper feed part; a discharge control part for controlling the discharge of ink droplets from the nozzle; a conveyance control part for controlling the conveyance of the recording medium; a head relative distance control part for controlling the relative distance of the inkjet head from the conveyance part; and form height detector which are arranged at a plurality of places different in the conveying direction of the recording medium and used for detecting the form height showing the amount of the recording medium to be lifted from the conveyance part. At least one of the conveyance of the recording medium, the discharge of the ink droplets, and the relative distance of the inkjet head from the conveyance part is controlled according to the detected form height of the recording medium. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method, and more particularly to an image forming apparatus and an image forming method provided with an inkjet head.

  2. Description of the Related Art Conventionally, an image forming apparatus has an inkjet head in which a large number of nozzles (ink discharge ports) are arranged, and a recording medium is conveyed relative to the inkjet head, and ink is directed from the nozzle toward the recording medium. An ink jet printer (ink jet recording apparatus) that forms an image on a recording medium by ejecting it as ink droplets is known.

  In such an ink jet printer, when the ink jet head and the recording medium are transported relative to each other, the nozzles of the ink jet head are close to the recording medium being transported. In some cases, dirt may adhere to the nozzle surface, the nozzle surface may be damaged, or paper dust may clog the nozzle, causing problems such as ejection failure.

  In order to deal with such problems, conventionally, for example, a lift detector for detecting the amount of lifting of the recording paper has been provided, and when a lifting of a predetermined amount or more of the recording paper is detected, interference with the nozzle portion of the inkjet head is caused. If recording is not performed on the floating part of the recording paper, and if such a floating part continues for a predetermined amount, the recording is stopped while the inkjet head is retracted from the range of the recording paper, and after the floating part has passed An ink jet recording apparatus that performs recording again is known (see, for example, Patent Document 1).

Japanese Patent No. 2733927

  Here, consider the case where the conventional technology is applied to an inkjet recording apparatus that continuously prints a large number of recording media at high speed. In order to avoid the collision between the recording medium being conveyed and the inkjet head and to prevent the recording medium from entering the lower part of the inkjet head, conventionally, a method of suddenly stopping the conveyance of the recording medium and a method of retracting the inkjet head, There is.

  In the case of high-speed printing, if an attempt is made to retract the inkjet head, it takes a certain time for the inkjet head to retract, and therefore it is necessary to dispose the lift detector and the inkjet head at some distance. Therefore, this distance increases as the recording medium conveyance speed increases, and this distance increases in the case of high-speed printing. At this time, if the recording medium is lifted or foreign matter adheres after passing through the lift detector, the recording medium collides with the inkjet head even though the lift is not detected when passing through the lift detector. There are things to do.

  On the other hand, when the method of suddenly stopping the conveyance of the recording medium is taken, it is a matter of course that printing is not performed on the recording medium in which an error has occurred, but because a large number of recording media are continuously printed. The recording medium before and after the recording medium also stops in the middle process (drying, fixing process, etc.). As a result, drying and fixing become insufficient, and print quality deteriorates. Therefore, these recording media must also be discarded, and there is a problem that throughput decreases.

  The present invention has been made in view of such circumstances. Even when printing a large number of recording media at high speed, the present invention suppresses a decrease in throughput and at the same time prevents contact between the inkjet head and the recording medium. An object of the present invention is to provide an image forming apparatus and an image forming method.

  In order to achieve the above object, the invention according to claim 1 is a recording comprising a sheet of paper at a position facing the ink jet head directly below the ink jet head, and an ink jet head having a nozzle for discharging ink droplets. A transport unit that transports the medium, a paper feed unit that feeds the recording medium to the transport unit, an ejection control unit that controls ejection of ink droplets from the nozzles, and transport of the recording medium by the transport unit An image forming apparatus including a conveyance control unit that controls the relative position of the inkjet head from the conveyance unit and a plurality of locations where the recording medium conveyance direction is different. Paper height detecting means for detecting the height of the recording medium indicating the amount of lifting of the recording medium from the conveying section, and detected by the paper height detecting means. And controlling at least one of conveyance of the recording medium, ejection of ink droplets from the nozzles, and relative distance from the conveyance unit of the inkjet head in accordance with the sheet height of the recording medium. An image forming apparatus is provided.

  As a result, even when a large number of recording media are printed at high speed, it is possible to suppress a decrease in throughput and at the same time prevent contact between the inkjet head and the recording medium. Note that in this specification, the paper height is a collective term of “paper height” such as paper floating, rising due to paper folding, or adhesion of foreign matter.

  According to a second aspect of the present invention, the sheet height detecting means includes a first sheet height detector disposed in the sheet feeding unit and a second sheet disposed in the transport unit in front of the inkjet head. And a sheet height detector.

  By providing the two sheet height detectors in this manner, the sheet floating state can be detected in detail, fine sheet conveyance and discharge control can be performed, and a decrease in throughput can be suppressed.

  According to a third aspect of the present invention, the conveyance control unit, the head relative distance control unit, and the discharge control unit are respectively connected to the conveyance unit and the inkjet head according to the detection result of the first paper height detector. The relative distance and the ejection of ink droplets from the nozzles are controlled.

  As a result, even when a large number of recording media are printed at high speed, it is possible to suppress a decrease in throughput and at the same time prevent contact between the inkjet head and the recording medium.

  According to a fourth aspect of the present invention, the head relative distance control unit that controls the relative distance of the inkjet head from the transport unit is a head height control unit that controls the height of the inkjet head on the transport unit. It is characterized by being.

  Thus, by controlling the height of the inkjet head with respect to the transport unit, it is possible not only to avoid collision with the recording medium but also to perform printing in some cases, and fine control is possible.

  According to a fifth aspect of the present invention, when the sheet height detected by the first sheet height detector is equal to or higher than a maximum value at which the inkjet head can be raised on the transport unit, the corresponding recording is performed. The medium stops feeding from the sheet feeding unit to the transport unit.

  As described above, when the detected paper height is very high and it is difficult to avoid the collision as it is, the collision can be avoided by stopping the feeding of the recording medium.

  According to a sixth aspect of the present invention, the paper height of the recording medium detected by the first paper height detector is less than a maximum value at which the ink jet head can rise on the transport unit, and the ink jet head The ink jet head is moved to a maximum height at which the ink jet head can be raised on the transport unit when the ink droplets are higher than a height at which the ink droplets can be ejected toward the recording medium. When the paper height of the recording medium detected by the second paper height detector is less than the maximum value at which the inkjet head can be raised on the transport unit, image formation is not performed on the corresponding recording medium. It is characterized by that.

  Thereby, after the paper height is detected by the first paper height detector, when the height of the inkjet head raised to avoid a collision is higher than the height at which ink droplets can be ejected, By not performing image formation, it is possible to prevent waste of the recording medium.

  According to a seventh aspect of the present invention, the height of the recording medium detected by the first paper height detector is a height at which the ink droplets can be ejected from the inkjet head toward the recording medium. Less than the height above the transport portion of the inkjet head at the time of normal image formation, the height at which the ink droplets can be ejected from the inkjet head toward the recording medium The sheet height of the recording medium detected again by the second sheet height detector is less than a height at which the ink droplets can be ejected from the inkjet head toward the recording medium. In this case, an image is formed on the corresponding recording medium, and the height of the inkjet head on the conveyance unit is usually set at a portion other than the image forming area of the corresponding recording medium. Performing ejection of ink droplets from a height or more positions at the time of image formation, wherein the attaching a mark indicating that the image formation.

  As a result, when an image is formed by ejecting ink droplets from a position higher than the height at the time of normal image formation, the user is informed to that effect and the image quality is judged by the user, thereby reducing the throughput. Suppress.

  In addition, as described in claim 8, the paper height of the recording medium by the second paper height detector is greater than the detection result of the paper height of the recording medium by the first paper height detector. When the detected result becomes larger, the conveyance is stopped before the recording medium reaches the lower part of the inkjet head.

  As a result, after the sheet height is detected by the first sheet height detector, if the sheet floats or adheres to the foreign matter on the recording medium, the conveyance is suddenly performed before the recording medium collides with the inkjet head. Avoid collisions by stopping.

  Similarly, in order to achieve the above-mentioned object, the invention according to claim 9 is configured such that a recording medium made of a sheet supplied from a sheet feeding unit is conveyed to the lower part of the inkjet by the conveyance unit, and the nozzle of the inkjet head An image forming method for forming an image on the recording medium by ejecting ink droplets from the recording medium to the recording medium, wherein the conveyance of the recording medium arranged at a plurality of locations in different conveyance directions of the recording medium Depending on the detection result by the paper height detecting means for detecting the paper height indicating the amount of lifting from the part, the recording medium is transported, the ink droplets are ejected from the nozzles, and the ink jet head is transported from the transport part. Provided is an image forming method characterized by controlling at least one of the relative distances.

  As a result, even when a large number of recording media are printed at high speed, it is possible to suppress a decrease in throughput and at the same time prevent contact between the inkjet head and the recording medium.

  According to a tenth aspect of the present invention, the sheet height detecting means includes a first sheet height detector disposed in the sheet feeding unit and a second sheet disposed in the transport unit in front of the inkjet head. And a sheet height detector.

  Thus, by providing two sheet height detectors, the sheet floating state can be detected in detail, fine sheet conveyance and discharge control can be performed, and a decrease in throughput can be suppressed.

  According to another aspect of the present invention, when the sheet height of the recording medium detected by the first sheet height detector is equal to or higher than a maximum value at which the inkjet head can be raised on the transport unit. The recording medium stops feeding paper from the paper feeding unit to the transport unit.

  Thereby, when the detected sheet height is very high and it is difficult to avoid the collision as it is, the collision can be avoided by stopping the feeding of the recording medium.

  Further, according to a twelfth aspect of the present invention, the sheet height of the recording medium detected by the first sheet height detector is less than a maximum value at which the inkjet head can be raised on the transport unit, and the inkjet head The ink jet head is moved to a maximum height at which the ink jet head can be raised on the transport unit when the ink droplets are higher than a height at which the ink droplets can be ejected toward the recording medium. When the paper height of the recording medium detected by the second paper height detector is less than the maximum value at which the inkjet head can be raised on the transport unit, image formation is not performed on the corresponding recording medium. It is characterized by that.

  Thereby, after the paper height is detected by the first paper height detector, when the height of the inkjet head raised to avoid a collision is higher than the height at which ink droplets can be ejected, By not performing image formation, it is possible to prevent waste of the recording medium.

  According to a thirteenth aspect of the present invention, the sheet height of the recording medium detected by the first sheet height detector is a height at which the ink droplets can be ejected from the inkjet head toward the recording medium. Less than the height above the transport portion of the inkjet head at the time of normal image formation, the height at which the ink droplets can be ejected from the inkjet head toward the recording medium The sheet height of the recording medium detected again by the second sheet height detector is less than a height at which the ink droplets can be ejected from the inkjet head toward the recording medium. In this case, image formation is performed on the corresponding recording medium, and the height of the inkjet head on the conveyance unit passes through a portion other than the image forming area of the recording medium. Characterized in that attaching a mark indicating that the image formed from the height or more positions at the time of image formation by performing ejection of ink droplets.

  As a result, when an image is formed by ejecting ink droplets from a position higher than the height at the time of normal image formation, the user is informed to that effect and the image quality is judged by the user, thereby reducing the throughput. Suppress.

  In addition, according to a fourteenth aspect of the present invention, the sheet height of the recording medium by the second sheet height detector is greater than the detection result of the sheet height of the recording medium by the first sheet height detector. When the detected result becomes larger, the conveyance is stopped before the recording medium reaches the lower part of the inkjet head.

  As a result, after the sheet height is detected by the first sheet height detector, if the sheet floats or adheres to the foreign matter on the recording medium, the conveyance is suddenly performed before the recording medium collides with the inkjet head. Avoid collisions by stopping.

  As described above, according to the present invention, even when a large number of recording media are printed at high speed, it is possible to suppress a decrease in throughput and simultaneously prevent contact between the inkjet head and the recording medium. Become.

1 is a schematic configuration diagram illustrating an embodiment of an ink jet recording apparatus as an image forming apparatus according to the present invention. It is a principal block diagram showing the system configuration of the ink jet recording apparatus. 6 is a flowchart illustrating an operation sequence relating to detection of paper floating and subsequent processing in the image forming method of the present embodiment.

  Hereinafter, an image forming apparatus and an image forming method according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram showing an embodiment of an ink jet recording apparatus as an image forming apparatus according to the present invention.

  The ink jet recording apparatus 100 uses a plurality of colors of ink from ink jet heads 172M, 172K, 172C, and 172Y on a recording medium 124 (hereinafter also simply referred to as “paper”) held on an impression cylinder (drawing drum 170) of the drawing unit 116. Is an impression cylinder direct drawing type ink jet recording apparatus that forms a desired color image by applying droplets to a processing liquid (here, an aggregating processing liquid) applied on the recording medium 124 before ink droplets are discharged. Is an on-demand type image forming apparatus to which a two-liquid reaction (aggregation) method in which an ink liquid is reacted to form an image on a recording medium 124 is applied.

  That is, as shown in FIG. 1, the inkjet recording apparatus 100 mainly includes a paper feeding unit 112, a treatment liquid application unit 114, a drawing unit 116, a drying unit 118, a fixing unit 120, and a paper discharge unit 122. ing.

  The paper feeding unit 112 is a mechanism that supplies the recording medium 124 to the processing liquid application unit 114, and the recording medium 124 that is a sheet is stacked on the paper feeding unit 112. The paper feed unit 112 is provided with a paper feed tray 150, and the recording medium 124 is fed from the paper feed tray 150 to the processing liquid application unit 114 one by one. In order to prevent the recording medium 124 from being lifted, the paper feed tray 150 may be provided with a suction hole on the outer surface, and a suction unit that performs suction from the suction hole may be connected.

  In the inkjet recording apparatus 100 of this example, a plurality of types of recording media 124 having different paper types and sizes (paper sizes) can be used as the recording medium 124. A mode is also possible in which a plurality of paper trays (not shown) are provided in the paper feed unit 112 to distinguish and collect various recording media and the paper to be fed to the paper feed tray 150 is automatically switched from among the plurality of paper trays. In addition, a mode is also possible in which the operator selects or replaces the paper tray as necessary. In this example, a sheet (cut paper) is used as the recording medium 124, but a configuration in which continuous paper (roll paper) is cut to a required size and fed is also possible.

  The processing liquid application unit 114 is a mechanism that applies the processing liquid to the recording surface of the recording medium 124. The treatment liquid contains a color material aggregating agent that agglomerates the color material (pigment in this example) in the ink applied by the drawing unit 116, and the ink comes into contact with the treatment liquid and the ink. And the solvent are promoted.

  As shown in FIG. 1, the treatment liquid application unit 114 includes a paper feed drum 152, a treatment liquid drum 154, and a treatment liquid application device 156. The treatment liquid drum 154 is a drum that holds and rotates the recording medium 124. The processing liquid drum 154 includes a claw-shaped holding means (gripper) 155 on the outer peripheral surface thereof, and the recording medium 124 is sandwiched between the claw of the holding means 155 and the peripheral surface of the processing liquid drum 154. The tip can be held. The treatment liquid drum 154 may be provided with a suction hole on the outer peripheral surface thereof and connected to a suction unit that performs suction from the suction hole. As a result, the recording medium 124 can be held in close contact with the peripheral surface of the treatment liquid drum 154.

  A processing liquid coating device 156 is provided outside the processing liquid drum 154 so as to face the peripheral surface thereof. The processing liquid coating device 156 includes a processing liquid container in which the processing liquid is stored, an anix roller partially immersed in the processing liquid in the processing liquid container, and the recording medium 124 on the anix roller and the processing liquid drum 154. And a rubber roller that transfers the measured processing liquid to the recording medium 124. According to the processing liquid coating apparatus 156, the processing liquid can be applied to the recording medium 124 while being measured.

  In the present embodiment, the configuration in which the application method using the roller is exemplified, but the present invention is not limited to this. For example, various methods such as a spray method and an ink jet method can be applied.

  The recording medium 124 to which the processing liquid is applied by the processing liquid applying unit 114 is transferred from the processing liquid drum 154 to the drawing drum 170 of the drawing unit 116 via the intermediate transport unit 126.

  The drawing unit 116 includes a drawing drum 170 and inkjet heads 172M, 172K, 172C, and 172Y. Although not shown in FIG. 1, a sheet suppression roller for removing the wrinkles of the recording medium 124 is disposed on the front side of the ink jet heads 172M, 172K, 172C, and 172Y with respect to the drawing drum 170. Also good.

  Similar to the processing liquid drum 154, the drawing drum 170 includes a claw-shaped holding unit (gripper) 171 that holds and fixes the leading end of the recording medium on the outer peripheral surface thereof. The recording medium 124 fixed to the drawing drum 170 is conveyed so that the recording surface faces outward, and ink is applied to the recording surface from the inkjet heads 172M, 172K, 172C, 172Y.

  The inkjet heads 172M, 172K, 172C, and 172Y are full-line inkjet recording heads (inkjet heads) each having a length corresponding to the maximum width of the image forming area on the recording medium 124. Is formed with a nozzle row in which a plurality of nozzles for ink ejection are arranged over the entire width of the image forming area. Each inkjet head 172M, 172K, 172C, 172Y is installed so as to extend in a direction orthogonal to the conveyance direction of the recording medium 124 (the rotation direction of the drawing drum 170).

  The droplets of the corresponding color ink are ejected from the inkjet heads 172M, 172K, 172C, and 172Y toward the recording surface of the recording medium 124 held in close contact with the drawing drum 170, whereby the processing liquid application unit 114 The ink comes into contact with the treatment liquid previously applied to the recording surface, and the color material (pigment) dispersed in the ink is aggregated to form a color material aggregate. As a result, the color material flow on the recording medium 124 is prevented, and an image is formed on the recording surface of the recording medium 124.

  In this example, the configuration of CMYK standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink, dark ink, and special ink are used as necessary. Color ink may be added. For example, it is possible to add an ink jet head that discharges light ink such as light cyan and light magenta, and the arrangement order of the color heads is not particularly limited.

  The drawing unit 116 configured as described above can perform drawing on the recording medium 124 in a single pass.

  The recording medium 124 on which an image is formed by the drawing unit 116 is transferred from the drawing drum 170 to the drying drum 176 of the drying unit 118 via the intermediate conveyance unit 128.

  The drying unit 118 is a mechanism that dries moisture contained in the solvent separated by the color material aggregating action, and includes a drying drum 176 and a solvent drying device 178 as shown in FIG.

  Similar to the processing liquid drum 154, the drying drum 176 includes a claw-shaped holding unit (gripper) 177 on the outer peripheral surface thereof, and the holding unit 177 can hold the leading end of the recording medium 124.

  The solvent drying device 178 is disposed at a position facing the outer peripheral surface of the drying drum 176, and includes a plurality of halogen heaters 180 and hot air ejection nozzles 182 disposed between the halogen heaters 180.

  Various drying conditions can be realized by appropriately adjusting the temperature and air volume of the hot air blown toward the recording medium 124 from each hot air ejection nozzle 182 and the temperature of each halogen heater 180.

  The surface temperature of the drying drum 176 is set to 50 ° C. or higher. Drying is accelerated by heating from the back surface of the recording medium 124, and image destruction during fixing can be prevented. The upper limit of the surface temperature of the drying drum 176 is not particularly limited, but from the viewpoint of safety of maintenance work such as cleaning ink adhering to the surface of the drying drum 176 (preventing burns due to high temperatures). It is preferably set to 75 ° C. or lower (more preferably 60 ° C. or lower).

  It is held on the outer peripheral surface of the drying drum 176 so that the recording surface of the recording medium 124 faces outward (that is, in a state in which the recording surface of the recording medium 124 is curved so as to be convex), and is dried while being rotated and conveyed. By doing so, it is possible to prevent the recording medium 124 from wrinkling and floating, and to reliably prevent drying unevenness caused by these.

  The recording medium 124 that has been dried by the drying unit 118 is transferred from the drying drum 176 to the fixing drum 184 of the fixing unit 120 via the intermediate conveyance unit 130.

  The fixing unit 120 includes a fixing drum 184, a halogen heater 186, a fixing roller 188, and an inline sensor 190. Like the processing liquid drum 154, the fixing drum 184 includes a claw-shaped holding unit (gripper) 185 on the outer peripheral surface, and the leading end of the recording medium 124 can be held by the holding unit 185.

  With the rotation of the fixing drum 184, the recording medium 124 is conveyed with the recording surface facing outward. The recording surface is preheated by the halogen heater 186, fixing processing by the fixing roller 188, and by the inline sensor 190. Inspection is performed.

  The halogen heater 186 is controlled to a predetermined temperature (for example, 180 ° C.). Thereby, preheating of the recording medium 124 is performed.

  The fixing roller 188 is a roller member that heats and pressurizes the dried ink to weld the self-dispersing polymer fine particles in the ink to form a film of the ink, and is configured to heat and press the recording medium 124. The Specifically, the fixing roller 188 is disposed so as to be in pressure contact with the fixing drum 184 and constitutes a nip roller with the fixing drum 184. As a result, the recording medium 124 is sandwiched between the fixing roller 188 and the fixing drum 184 and nipped at a predetermined nip pressure (for example, 0.15 MPa), and the fixing process is performed.

  The fixing roller 188 is configured by a heating roller in which a halogen lamp is incorporated in a metal pipe such as aluminum having good thermal conductivity, and is controlled to a predetermined temperature (for example, 60 to 80 ° C.). By heating the recording medium 124 with this heating roller, thermal energy equal to or higher than the Tg temperature (glass transition temperature) of the latex contained in the ink is applied, and the latex particles are melted. As a result, pressing and fixing are performed on the unevenness of the recording medium 124, and the unevenness of the image surface is leveled to obtain glossiness.

  In the embodiment of FIG. 1, only one fixing roller 188 is provided. However, a configuration in which a plurality of fixing rollers 188 are provided may be used depending on the thickness of the image layer and the Tg characteristics of latex particles.

  On the other hand, the in-line sensor 190 is a measuring means for measuring a check pattern, a moisture content, a surface temperature, a glossiness, and the like for an image fixed on the recording medium 124, and a CCD line sensor or the like is applied.

  According to the fixing unit 120 configured as described above, the latex particles in the thin image layer formed by the drying unit 118 are heated and pressurized by the fixing roller 188 and are melted. Can be made. The surface temperature of the fixing drum 184 is set to 50 ° C. or higher. The recording medium 124 held on the outer peripheral surface of the fixing drum 184 is heated from the back surface to accelerate drying, thereby preventing image destruction at the time of fixing and increasing the image strength by the effect of increasing the image temperature. Can do.

  When an ink containing an actinic ray curable resin such as a UV curable resin is used instead of the ink containing the thermoplastic resin particles, a UV lamp or an ultraviolet LD is used instead of the fixing roller 188 for heat fixing. Means for irradiating actinic rays, such as (laser diode) arrays, are provided.

  Subsequent to the fixing unit 120, a paper discharge unit 122 is provided. A paper discharge unit 192 is installed in the paper discharge unit 122. Between the fixing drum 184 and the paper discharge unit 192 of the fixing unit 120, transfer cylinders 194 and 195 and a transport chain 196 are provided. The transport chain 196 is wound around stretching rollers 197 and 198. The recording medium 124 that has passed through the fixing drum 184 is sent to the transport chain 196 via the transfer drums 194 and 195, and is transferred from the transport chain 196 to the paper discharge unit 192.

  Although not shown in FIG. 1, the ink jet recording apparatus 100 of the present example has an ink storage / loading unit that supplies ink to each of the ink jet heads 172M, 172K, 172C, and 172Y, and a treatment liquid application, in addition to the above configuration. A head maintenance unit for supplying a processing liquid to the unit 114 and cleaning the ink jet heads 172M, 172K, 172C, 172Y (wiping, purging, nozzle suction, etc. of the nozzle surface) A position detection sensor for detecting the position of the recording medium 124, a temperature sensor for detecting the temperature of each part of the apparatus, and the like are provided.

  In the present embodiment, as a special configuration according to the present invention, two sheet floating sensors (paper height detecting means) for detecting the floating of the conveyed recording medium 124 are installed. That is, the first paper float sensor 200 is installed on the end of the paper feed tray 150 on the side close to the paper feed drum 152, and the second paper float sensor 202 is placed on the inkjet heads 172M and 172K of the drawing drum 170. It is installed on the outer peripheral surface on the near side of 172C and 172Y.

  Further, a stamp (printing means) 204 is provided on the outer peripheral surface of the transfer drum 194 of the paper discharge unit 122 for printing the mark on a print that seems to have a problem with image quality due to paper floating or the like. Has been. The stamp (printing means) 204 simply prints a mark indicating that there is a problem with the image quality of the print. Therefore, the stamp is the simplest printing means, but is not limited to the stamp. . For example, other printing means such as inkjet may be used.

  FIG. 2 is a principal block diagram showing the system configuration of the inkjet recording apparatus 100.

  The inkjet recording apparatus 100 includes a communication interface 80, a system controller (system controller) 82, an image memory 84, a motor driver 86, a heater driver 88, a print controller 90, a maintenance controller 92, a head driver 94, and the like.

  The communication interface 80 is an interface unit that receives image data sent from the host computer 96. As the communication interface 80, a serial interface such as USB (Universal Serial Bus), IEEE 1394, Ethernet (registered trademark), a wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory for speeding up communication may be mounted. The image data sent from the host computer 96 is taken into the ink jet recording apparatus 100 via the communication interface 80 and temporarily stored in the image memory 84.

  The image memory 84 is a storage unit that temporarily stores an image input via the communication interface 80, and data is read and written through the system control unit 82. The image memory 84 is not limited to a memory composed of semiconductor elements, and a magnetic medium such as a hard disk may be used.

  The system control unit 82 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 100 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. To do. That is, the system control unit 82 controls the communication interface 80, the image memory 84, the motor driver 86, the heater driver 88, and the like, and generates control signals for controlling the heater 99 and the host computer 96.

  The image memory 84 stores programs executed by the CPU of the system control unit 82 and various data necessary for control. Note that the image memory 84 may be a non-rewritable storage means or a rewritable storage means such as an EEPROM. The image memory 84 may be used as a temporary storage area for image data, and may be used as a program development area and a calculation work area for the CPU.

  The system control unit 82 is connected to an EEPROM 85 that stores various control programs and an image processing unit 87 that performs various image processes on image data. In response to a command from the system control unit 82, a control program is read from the EEPROM 85 and executed. Note that the EEPROM 85 may also be used as a storage unit for operating parameters and the like.

  The motor driver 86 is a driver that drives the motor 98 in accordance with an instruction from the system control unit 82. In FIG. 2, the motor (actuator) disposed in each part of the inkjet recording apparatus 100 is represented by reference numeral 98. For example, the motor 98 shown in FIG. 2 includes motors that drive the intermediate transport units 126 and 128, the transfer drum 152, the processing liquid drum 154, the drawing drum 170, the drying drum 176, the fixing drum 184, and the like shown in FIG.

  As will be described in detail later, if the sheet height rises due to the occurrence of sheet floating or adhesion of foreign matter to the recording medium 124 being conveyed and the sheet is conveyed as it is, the recording medium 124 collides with the inkjet heads 172M, 172K, 172C, 172Y. If there is a risk of this, the system control unit 82 performs control such as stopping the feeding and conveyance of the recording medium 124 via the motor driver 86.

  The heater driver 88 is a driver that drives the heater 99 in accordance with an instruction from the system control unit 82. In FIG. 2, a plurality of heaters provided in the ink jet recording apparatus 100 are represented by reference numeral 99. For example, the heater 99 shown in FIG. 2 includes the heater of the treatment liquid application unit 114 and the halogen heater of the drying unit 118 shown in FIG.

  In addition, a maintenance control unit 92 is connected to the system control unit 82. The maintenance control unit 92 controls a maintenance drive unit 93 that drives a maintenance unit (not shown) including a cap and a cleaning blade in accordance with an instruction from the system control unit 82.

  The print control unit 90 has a signal processing function for performing various processes and corrections for generating a print control signal from the image data in the image memory 84 under the control of the system control unit 82. The controller is a controller that controls the treatment liquid application driver 95 to apply the treatment liquid from the treatment liquid application device 156 to the recording medium 124 and supplies the generated print data (dot data) to the head driver 94. . Necessary signal processing is performed in the print controller 90, and the ejection droplet amount (droplet ejection amount) and ejection timing of the inkjet heads 172M, 172K, 172C, 172Y are controlled via the head driver 94 based on the image data. Is done. Thereby, a desired dot size and dot arrangement are realized.

  The print control unit 90 also controls the head driver 94 to stop printing on the recording medium 124 whose paper height has increased due to the occurrence of paper floating or foreign matter adhesion.

  The inline detection unit 91 performs non-ejection detection for determining an ejection failure nozzle based on information obtained from the inline sensor 190.

  When the inline detection unit 91 performs non-ejection detection, the system control unit determines whether or not the ejection abnormality nozzle is present, and performs image correction when the ejection abnormality nozzle can be corrected by image correction. A control signal is sent to each part via 82. If the image correction cannot cope, a control signal is sent to each unit via the system control unit 82 so as to perform a recovery operation such as preliminary discharge or suction for the abnormal discharge nozzle.

  In addition, the paper height detection unit 20 and the head height control unit 30 are connected to the system control unit 82. The print controller 90 is connected to a stamp driver 40 that controls a stamp (printing unit) 204.

  The paper height detection unit 20 includes the first paper floating sensor 200 installed on the end of the paper feed tray 150 on the side close to the paper feed cylinder 152, and the inkjet heads 172M, 172K, and 172C of the drawing drum 170. , 172Y on the outer peripheral surface on the near side, the second sheet floating sensor 202 is composed of two sheet floating sensors.

  The head height control unit 30 controls the relative position (height) of the inkjet heads 172M, 172K, 172C, 172Y with respect to the surface of the recording medium 124 conveyed on the drawing drum 170. As will be described in detail later, for example, when a sheet float occurs in the recording medium 124 being conveyed and the recording medium 124 is likely to collide with the inkjet heads 172M, 172K, 172C, 172Y, Control is performed to avoid a collision by increasing the height of the recording medium 124 of 172C and 172Y. The specific configuration for changing the height of the inkjet heads 172M, 172K, 172C, 172Y is not particularly limited, and a mechanical mechanism using gears such as a pinion rack can be applied. .

  In the present embodiment, the sheet height detection unit 20 includes the two sheet floating sensors 200 and 202 as described above. The sheet height detection unit 20 includes two sheets floating sensors 200 and 202. "Height").

  The sheet floating sensors 200 and 202 are not particularly limited, and general optical sensors can be used. For example, the sheet (recording medium 124) floats depending on how the light is blocked by receiving light from one direction and receiving light on the opposite side, or receiving a reflected light by disposing a reflective surface on the other side. It can be set as the structure which detects.

  Further, the distance between the recording medium 124 and the inkjet heads 172M, 172K, 172C, 172Y (hereinafter also simply referred to as the head 172) is normally set to 1 mm. Further, the head 172 has a distance of 3 mm from the surface of the recording medium when the recording medium 124 is normally conveyed without being lifted (normal recording medium surface corresponding to the height of the conveying drum surface plus the thickness of the recording medium 124). It is configured to be able to ascend and to stop at an intermediate position of 2 mm. Here, the height of 3 mm is the maximum value at which the head 172 can rise onto the transport unit, and the height of 2 mm is the limit of the height at which ink droplets can be ejected from the head 172 toward the recording medium 124. It is.

  The first paper float sensor 200 and the second paper float sensor 202 can measure whether or not there is an object at a height of 3 mm, 2 mm, and 1 mm from the normal recording medium surface. It is configured. That is, with respect to the sheet height of the recording medium 124 by the first sheet floating sensor 200 and the second sheet floating sensor 202, the distance (sheet height) lifted from the normal recording medium surface is (1) 1 mm. (2) 1 mm or more and less than 2 mm, (3) 2 mm or more and less than 3 mm, and (4) 3 mm or more.

  Hereinafter, an operation sequence relating to detection of sheet floating and subsequent processing in the image forming method of the present embodiment will be described with reference to the flowchart of FIG.

  First, in step S100 of FIG. 3, when the recording medium 124 is fed from the paper feed tray 150 of the paper feed unit 112 to the paper feed cylinder 152, the first paper float sensor 200 detects the paper height. Is called.

  If the detection result by the first sheet floating sensor 200 is that the sheet height H is 3 mm or more (H ≧ 3) (“Y” in step S100), the sheet feeding is stopped in step S102. This is because the head 172 can only rise up to a distance of 3 mm from the recording medium 124 (drawing drum 170), and thus cannot be escaped even if it rises. Further, although the feeding of the new recording medium 124 into the machine is stopped, the normal printing is performed on the recording medium 124 that has already been fed into the machine and remains in the previous machine from the feeding cylinder 152, and thereafter The paper is discharged from the paper discharge unit 122 through a process. Thereafter, an error message is displayed on the display screen (user screen) of the display unit (not shown in FIG. 1). The user sees the message and removes the recording medium 124 left in the apparatus due to the stop of paper feeding.

  If the sheet height H detected by the first sheet floating sensor 200 is less than 3 mm (H <3) in step S100 (“N” in step S100), the first sheet floating is performed in step S104. It is determined whether the sheet height H detected by the sensor 200 is 2 mm or more and less than 3 mm (2 ≦ H <3).

  If it is determined in step S104 that the sheet height H detected by the first sheet floating sensor 200 is 2 mm or more and less than 3 mm (2 ≦ H <3) (“Y” in step S104), in step S106, The head 172 is raised on the drawing drum 170 to a distance of 3 mm from the surface of the recording medium (normal recording medium surface) when the recording medium 124 is normally conveyed. Paper feeding is performed normally.

  At this time, since the detected paper height H is less than 3 mm, the contact of the recording medium 124 with the head 172 can be avoided by raising the head 172 by 3 mm above the normal recording medium surface.

  However, after the sheet height H is detected by the first sheet floating sensor 200, the recording medium 124 is conveyed to the drawing drum 170 of the drawing unit 116 through the paper feed cylinder 152, the processing liquid drum 154, and the intermediate conveyance unit 126. It is also possible that the paper height H rises for some reason, such as paper floating or foreign matter adhering. Therefore, in this embodiment, another sheet floating sensor, that is, the second sheet floating sensor 202 is provided immediately before the head 172 of the drawing drum 170, and the sheet height is detected again before image formation. Yes.

  In step S <b> 108, the paper height H is detected again immediately before the head 172 in the drawing unit 116 by the second paper floating sensor 202. If the second sheet floating sensor 202 detects that the sheet height H is 3 mm or more (H ≧ 3) (“Y” in step S108), the recording medium 124 and the head 172 collide with each other as they are. Therefore, in step S110, the conveyance of the recording medium 124 is suddenly stopped.

  In this case, the recording medium 124 transported before and after the paper including the corresponding paper whose paper height H is 3 mm or more is not treated as a normal printed product (print). Stocked separately.

  In step S108, when the second sheet floating sensor 202 detects that the sheet height H is less than 3 mm (H <3) (“N” in step S108), the corresponding sheet is detected in step S112. The paper is not printed, the paper is stocked separately from the normal printed product, and normal printing is performed on the paper before the paper.

  Here, the reason why printing is not performed on the corresponding sheet is that the head 172 is positioned at a height of 3 mm from the normal recording medium surface (see step S106), and ink is ejected from a height of 3 mm. This is because the distance (slow distance) from the head 172 to the recording medium 124 is too long and ink droplets do not normally adhere to the recording medium 124.

  If the second sheet floating sensor 202 detects that the sheet height H is less than 3 mm (H <3) (“N” in step S108), the head 172 now moves from the normal recording medium surface. Since the height is 3 mm, the recording medium 124 does not come into contact with the head 172, so that it is not necessary to stop the conveyance. Therefore, the previous recording medium 124 is treated as a normal print product.

  If it is determined in step S104 that the sheet height H by the first sheet floating sensor 200 is less than 2 mm (“N” in step S104), then in step S114, the first sheet floating sensor is detected. It is determined whether the sheet height H is 200 mm or more and less than 2 mm (1 ≦ H <2).

  If it is determined in step S114 that the sheet height H by the first sheet floating sensor 200 is 1 mm or more and less than 2 mm (1 ≦ H <2) (“Y” in step S114), the head 172 is moved in step S116. The sheet is raised to a height of 2 mm from the normal recording medium surface and fed normally.

  Thereafter, similarly to step S108, the sheet height H is detected again by the second sheet floating sensor 202 in step S118.

  At this time, if the sheet height H increases for some reason and the sheet height H is detected to be 2 mm or more ("Y" in step S118), the head 172 and the recording medium 124 collide with each other as it is. In step S120, the conveyance of the recording medium 124 is suddenly stopped. The recording medium 124 transported before and after the corresponding recording medium 124 is not handled as a normal print product, and is stocked separately from the normal print product.

  On the other hand, when the sheet height H is detected by the second sheet floating sensor 202 to be less than 2 mm in step S118 (“N” in step S118), it is positioned at a height of 2 mm as it is in step S122. The ink is ejected from the head 172 toward the recording medium 124 to perform printing, and stocked as a normal printed product. Also in this case, since it is not necessary to stop the conveyance, the previous recording medium 124 is treated as a normal print product.

  However, in this case, since the printing is not from a normal height (1 mm), the image quality cannot be guaranteed, so a stamp (printing means) installed on the outer peripheral surface of the transfer cylinder 194 of the paper discharge unit 122 In 204, a mark indicating that there is a problem with the image quality is stamped in the non-image forming area of the printed material, and the fact is also displayed on the user screen of the display unit (not shown). The user looks at the display information to recognize the presence of a printed product that has not been printed from a normal height, and determines whether the image quality of the printed product having the stamp mark is sufficient.

  Next, in step S114, when the sheet height H detected by the first sheet floating sensor 200 is less than 1 mm (“N” in step S114), the head 172 is moved to the normal recording medium in step S124. Move to a position of 1 mm from the surface. The recording medium 124 is conveyed normally.

  In step S126, the second sheet floating sensor 202 detects the sheet height H. Here, when the paper height H is 1 mm or more (H ≧ 1) (“Y” in step S126), the paper height H of the recording medium 124 has increased for some reason, and the head is left as it is. Since 172 and the recording medium 124 collide, in step S128, the conveyance of the recording medium 124 is suddenly stopped. The recording medium 124 transported before and after the corresponding recording medium 124 is not handled as a normal printed product, and is stocked separately from the normal printed product.

  On the other hand, when the sheet height H is detected by the second sheet floating sensor 202 to be less than 1 mm in step S126 (“N” in step S126), this is a normal case. In step S130, Normal printing is performed.

  By performing processing according to the operation flow described in detail above, it is possible to suppress a decrease in throughput when printing a large number of recording media at high speed, and to prevent contact between the head and the recording medium. In addition, since two paper float sensors are provided, not only when the paper height is high, paper feeding is stopped, but the situation is divided into a plurality of cases, and fine control according to each case is performed. Is possible.

  In the example described above, the head 172 is raised with respect to the recording medium 124 to adjust the height. However, the method for avoiding the collision between the recording medium 124 and the head 172 is not limited to this. Instead of moving the head 172 upward, the recording medium 124 may be moved downward. Further, for example, the head 172 may be controlled to move in a direction (lateral direction) orthogonal to the conveyance direction of the recording medium 124. Eventually, in order to avoid a collision between the head 172 and the recording medium 124, control may be performed so that the relative distance between the head 172 and the recording medium 124 is increased. At this time, the head height control unit 30 in FIG. 2 becomes a head distance control unit. However, when the head 172 is released in the horizontal direction, it is not possible to print on the corresponding sheet.

  As another method for avoiding the collision, for example, two transport paths are prepared in the transport section following the paper feed section, and a first sheet floating sensor is arranged in front of the branching point. When the paper floating sensor detects a paper height of 3 mm or more, the conveyance path is switched at the branch point, and the recording medium is guided to a conveyance path different from the conveyance path going to the normal head side, and discharged. There is also a way to do it.

  According to this method, even when the paper height is as high as 3 mm or more and the collision cannot be avoided even if the head is raised, only the corresponding recording medium is transported to the transport path different from the normal one, and the head side is moved. By avoiding this, it is possible to avoid collisions and continue feeding without stopping the feeding of other recording media, so recording media are not wasted and throughput is reduced. Nor.

  In the embodiment described above, the inkjet heads 172M, 172K, 172C, and 172Y are full-line inkjet recording heads each having a length corresponding to the maximum width of the image forming area in the recording medium 124. However, a shuttle (serial) type ink jet head may be used.

  The image forming apparatus and the image forming method of the present invention have been described in detail above. However, the present invention is not limited to the above examples, and various improvements and modifications are made without departing from the gist of the present invention. Of course it is also good.

  DESCRIPTION OF SYMBOLS 20 ... Paper height detection part, 30 ... Head height control part, 40 ... Stamp driver, 82 ... System control part, 86 ... Motor driver, 90 ... Print control part, 100 ... Inkjet recording device, 112 ... Paper feed part, DESCRIPTION OF SYMBOLS 114 ... Processing liquid provision part, 116 ... Drawing part, 118 ... Drying part, 120 ... Fixing part, 122 ... Paper discharge part, 124 ... Recording medium, 170 ... Drawing drum, 171 ... Holding means (gripper), 172M, 172K, 172C, 172Y ... inkjet head, 200 ... first paper float sensor, 202 ... second paper float sensor, 204 ... stamp (printing means)

Claims (14)

An ink jet head having a nozzle for discharging ink droplets; a transport unit that transports a recording medium made of a sheet to a position facing the ink jet head immediately below the ink jet head; and the recording medium is supplied to the transport unit. An image forming apparatus comprising: a paper feeding unit for paper; an ejection control unit that controls ejection of ink droplets from the nozzle; and a conveyance control unit that controls conveyance of the recording medium by the conveyance unit,
A head relative distance control unit that controls a relative distance of the inkjet head from the transport unit;
A sheet height detecting means for detecting a sheet height indicating the amount of lifting of the recording medium from the conveying section, which is disposed at a plurality of locations different in the conveying direction of the recording medium;
According to the paper height of the recording medium detected by the paper height detecting means, relative to the transport of the recording medium, the ejection of ink droplets from the nozzles, and the transport portion of the inkjet head An image forming apparatus that controls at least one of the distances.   The sheet height detecting means includes a first sheet height detector disposed in the sheet feeding unit and a second sheet height detector disposed in the transport unit in front of the inkjet head. The image forming apparatus according to claim 1.   In accordance with the detection result of the first paper height detector, the transport control unit, the head relative distance control unit, and the ejection control unit respectively transfer the ink from the transport unit, the relative distance of the inkjet head, and the nozzle. The image forming apparatus according to claim 2, wherein ejection of droplets is controlled.   2. The head relative distance control unit that controls a relative distance of the inkjet head from the transport unit is a head height control unit that controls a height of the inkjet head on the transport unit. The image forming apparatus according to any one of?   When the paper height detected by the first paper height detector is equal to or higher than the maximum value at which the inkjet head can be raised on the transport unit, the corresponding recording medium is transported from the paper feed unit to the transport unit. The image forming apparatus according to claim 2, wherein paper feeding to the printing unit is stopped.   The sheet height of the recording medium detected by the first sheet height detector is less than a maximum value at which the inkjet head can rise on the transport unit, and the ink liquid is directed from the inkjet head toward the recording medium. The second paper height detector detects the ink-jet head after the ink-jet head has moved to a maximum height at which the ink-jet head can rise onto the transport unit when the height is greater than the height at which droplets can be ejected. 6. An image is not formed on the recording medium when the sheet height of the recording medium is less than a maximum value at which the inkjet head can be raised on the transport unit. The image forming apparatus according to any one of the above.   The sheet height of the recording medium detected by the first sheet height detector is less than the height at which the ink droplets can be ejected from the inkjet head toward the recording medium, and the recording medium is formed during normal image formation. When the height of the ink jet head is greater than or equal to the height on the transport unit, the ink jet head is moved from the ink jet head toward the recording medium to a height at which the ink droplets can be discharged, and then the second If the paper height of the recording medium detected again by the paper height detector is less than the height at which the ink droplets can be ejected from the inkjet head toward the recording medium, When the image is formed and the height of the ink jet head on the conveyance unit is higher than the height at the time of normal image formation in a portion other than the image formation area of the recording medium. The image forming apparatus according to any one of claims 2-6, characterized in that attaching a marker to perform ejection of ink droplets from the position indicating that the image formed.   The detection result of the paper height of the recording medium by the second paper height detector is greater than the detection result of the paper height of the recording medium by the first paper height detector. The image forming apparatus according to claim 2, wherein the conveyance of the recording medium is stopped before reaching the lower part of the inkjet head. A recording medium made of a sheet supplied from the paper feeding unit is conveyed to the lower part of the inkjet by the conveying unit, and ink droplets are ejected from the nozzles of the inkjet head onto the recording medium, thereby forming an image on the recording medium. An image forming method for forming,
Conveying the recording medium according to the detection result by the paper height detecting means for detecting the paper height indicating the amount of lifting of the recording medium from the conveying unit disposed at a plurality of locations different in the conveying direction of the recording medium. An image forming method comprising controlling at least one of ejection of an ink droplet from the nozzle and a relative distance from the transport portion of the inkjet head.   The sheet height detecting means includes a first sheet height detector disposed in the sheet feeding unit and a second sheet height detector disposed in the transport unit in front of the inkjet head. The image forming method according to claim 9.   When the sheet height of the recording medium detected by the first sheet height detector is equal to or higher than the maximum value at which the inkjet head can be raised on the transport unit, the corresponding recording medium is The image forming method according to claim 10, wherein the sheet feeding from the section to the transport section is stopped.   The sheet height of the recording medium detected by the first sheet height detector is less than a maximum value at which the inkjet head can rise on the transport unit, and the ink liquid is directed from the inkjet head toward the recording medium. The second paper height detector detects the ink-jet head after the ink-jet head has moved to a maximum height at which the ink-jet head can rise onto the transport unit when the height is greater than the height at which droplets can be ejected. 12. The image formation is not performed on the recording medium when the sheet height of the recording medium is less than a maximum value at which the inkjet head can be raised on the transport unit. The image forming method described in 1.   The sheet height of the recording medium detected by the first sheet height detector is less than the height at which the ink droplets can be ejected from the inkjet head toward the recording medium, and the recording medium is formed during normal image formation. When the height of the ink jet head is greater than or equal to the height on the transport unit, the ink jet head is moved from the ink jet head toward the recording medium to a height at which the ink droplets can be ejected, and then the second If the paper height of the recording medium detected again by the paper height detector is less than the height at which the ink droplets can be ejected from the inkjet head toward the recording medium, When the image is formed and the height of the ink jet head on the conveyance unit is higher than the height at the time of normal image formation in a portion other than the image forming area of the recording medium. The image forming method according to any one of claims 10 to 12, characterized in that attaching a mark indicating that performs the ejection of ink droplets and the image forming from the position.   The detection result of the paper height of the recording medium by the second paper height detector is greater than the detection result of the paper height of the recording medium by the first paper height detector. The image forming method according to claim 10, wherein the conveyance of the recording medium is stopped before reaching the lower part of the inkjet head.

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