JP2012143944A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an image forming means from contacting a recording medium.SOLUTION: The image forming apparatus includes: a prediction means that predicts a second lift amount of the recording medium 124 in a position opposite to an inkjet head 172 based on a plurality of first lift amounts detected by each lift amount detection sensor 204; and a control means that decreases a conveyance speed of a drawing drum 170 or makes the inkjet head 172 retreat from the drawing drum 170 based on the second lift amount that the prediction means predicts.

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, an image forming apparatus has a droplet discharge head in which a large number of nozzles are arranged. A recording medium is conveyed relative to the droplet discharge head and ink or the like is directed from the nozzle toward the recording medium. 2. Description of the Related Art A liquid discharge recording type image forming apparatus that forms an image (including characters) on a recording medium by discharging droplets is known.

  In such a liquid discharge recording type image forming apparatus, since the nozzle surface of the droplet discharge head is close to the recording medium and discharges the droplet, depending on the orientation of the recording medium, the recording medium may come into contact with the nozzle and the recording is performed. In some cases, dirt may adhere to the medium, or the nozzle surface may be damaged, or paper dust may clog the nozzle, causing problems such as ejection failure.

  Also in image forming apparatuses other than the liquid discharge recording method, there is a concern that the recording medium comes into contact with the image forming means instead of the droplet discharge head, and the image quality is lowered.

  In order to solve such a problem, Patent Document 1 discloses that when a lift detector (a lift amount detecting unit) that detects a lift amount of a recording medium detects a lift of a predetermined amount or more of a recording medium, a droplet is detected. An image forming apparatus is disclosed in which recording is stopped by retracting an ejection head from a recording medium.

  Patent Document 2 discloses an image forming apparatus that detects an abnormality in the conveyance of a recording medium based on a detection result of a sensor (a lifting amount detection unit) that detects a distance to the recording medium conveyed by the conveyance mechanism. Has been.

Japanese Patent No. 2733927 Japanese Patent No. 3951858

  However, in the case of the configurations of Patent Document 1 and Patent Document 2, when a lift occurs in the recording medium after passing through the lift amount detection means such as a lift detector, the lift is not detected when passing through the lift amount detection means. Nevertheless, the recording medium may come into contact with the image forming means.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of preventing contact between an image forming unit and a recording medium.

  The image forming apparatus according to the first aspect of the present invention includes: an image forming unit that forms an image on a recording medium; a transport unit that transports the recording medium to a position facing the image forming unit; A plurality of lifting amount detection means that are arranged at different locations in the transport direction on the upstream side in the transport direction of the recording medium and detect a first lifting amount from the transport means when the recording medium passes; Prediction means for predicting a second lift amount of the recording medium at a position facing the image forming means based on the first lift amount of the recording medium at the time of passage detected by the lift amount detection means; and the prediction means Control means for reducing the conveying speed of the conveying means or retracting the image forming means from the conveying means based on the second lifting amount predicted by Provided.

  According to this configuration, the predicting unit predicts the second lifting amount at the position facing the image forming unit based on the plurality of first lifting amounts detected when the recording medium passes through each lifting amount detection unit. The control unit lowers the transport speed of the transport unit (including stopping the transport unit) or retracts the image forming unit from the transport unit based on the second lifting amount predicted by the prediction unit. Contact with the recording medium can be prevented.

  The image forming apparatus according to a second aspect of the present invention is the image forming apparatus according to the first aspect, wherein the distance between the lift amount detecting means on the most downstream side in the transport direction and the image forming means among the lift amount detecting means is It is set longer than the paper conveyance braking distance.

  According to this configuration, before the recording medium is transported to a position facing the image forming unit, the transport speed of the transport unit decreases or the image forming unit is completely retracted from the transport unit. Contact between the means and the recording medium can be reliably prevented.

  In the image forming apparatus according to the third aspect of the present invention, in the first aspect or the second aspect, the conveying means is a drawing cylinder that rotates and conveys the recording medium, and the image forming means A droplet discharge head including a nozzle for discharging, provided on the upstream side in the transport direction of the recording medium from the droplet discharge head, and includes a sheet pressing member that presses the recording medium transported by the drawing cylinder, The lifting amount detection means is disposed at a plurality of locations between the sheet pressing member and the droplet discharge head.

  According to this configuration, even if the recording medium is lifted after the recording medium passes through the paper pressing member, the first lifting amount between the paper pressing member and the droplet discharge head is set to the paper pressing member. Detection can be made by means of floating amount detection means arranged at a plurality of locations between the droplet discharge heads. For this reason, the prediction of the second lifting amount by the prediction means is also accurate.

  In the image forming apparatus according to a fourth aspect of the present invention, in the third aspect, the predicting unit is configured to have the plurality of first lifting amounts detected by the lifting amount detection unit and after the recording medium has passed the sheet pressing member. And the control means predicts the second lifting amount at the time when the recording medium reaches the position facing the droplet discharge head, and the control means predicts the second amount predicted by the prediction means. 2. When the lifting amount is equal to or greater than a preset distance between the conveying means and the recording medium, the conveying means is controlled to stop conveying the recording medium.

  According to this configuration, since the recording medium stops before the droplet discharge head, contact between the droplet discharge head and the recording medium can be reliably prevented.

  In the image forming apparatus according to the fifth aspect of the present invention, in the fourth aspect, the predicting means includes a plurality of first lifts during which the time after the recording medium passes through the paper pressing member is less than 200 milliseconds. Based on the amount, the first lifting amount at 200 milliseconds is predicted linearly, and the predicted first lifting amount is set as the second lifting amount.

  According to this configuration, the first lifting amount predicted at 200 milliseconds after the recording medium passes through the sheet pressing member is actually the time when the recording medium reaches the position facing the droplet discharge head. The second lifting amount is not excessively predicted because it is based on the rule of thumb that the second lifting amount is substantially the same.

  An image forming apparatus according to a sixth aspect of the present invention is the image forming apparatus according to the fourth aspect, wherein the relationship between the time after the recording medium passes through the paper pressing member, the first lifting amount, and the second lifting amount is expressed as data. Storage means storing a plurality of tables corresponding to each other, and the prediction means, among the tables stored in the storage means, each first lift amount when detected by the lift amount detection means, The table having the closest data is selected, and the second lifting amount in the selected table is output to the control means.

  According to this configuration, in order for the prediction means to predict the second lift amount, one of the first lift amounts when detected by the lift amount detection means among the tables stored in the storage means, Since it is only necessary to select a table having the closest data and output the second lifting amount in the selected table to the control means, the prediction of the second lifting amount is accelerated.

  According to the present invention, it is possible to provide an image forming apparatus capable of preventing contact between an image forming unit and a recording medium.

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. FIG. 2 is an enlarged view showing a recording medium conveying apparatus which is a main part of the ink jet recording apparatus according to the first embodiment. FIG. 3 is a principal block diagram showing the system configuration of the ink jet recording apparatus according to the first embodiment of the present invention. FIG. 4 is a flowchart showing an operation sequence related to detection of the floating amount of the recording medium and subsequent processing in the image forming method of the present embodiment. FIGS. 5A to 5C are views showing the state of the recording medium conveyed by the drawing drum.

(First embodiment)
The image forming apparatus according to the first embodiment of the present invention will be specifically described below with reference to the accompanying drawings. In the drawings, members (components) having the same or corresponding functions are denoted by the same reference numerals and description thereof is omitted as appropriate.

  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 the inkjet recording apparatus 100 according to the present embodiment, 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.

  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.

  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 ink jet heads 172M, 172K, 172C, and 172Y (hereinafter sometimes collectively referred to as an ink jet head 172).

  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.

  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.

  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, in addition to the above-described configuration, the inkjet recording apparatus 100 of the present embodiment includes an ink storage / loading unit that supplies ink to each inkjet head 172M, 172K, 172C, and 172Y, and a processing liquid. A means for supplying a treatment liquid to the applying unit 114 and a head maintenance unit for cleaning each of the inkjet heads 172M, 172K, 172C, and 172Y (wiping, purging, nozzle suction, etc. of the nozzle surface), and on the paper conveyance path Are provided with a position detection sensor for detecting the position of the recording medium 124 and a temperature sensor for detecting the temperature of each part of the apparatus.

  Of the configuration of the ink jet recording apparatus 100 described above, the processing liquid drum 154, the drawing drum 170, the drying drum 176, the fixing drum 184, and the intermediate conveyance units 126, 128, 130 between them, etc. This constitutes the recording medium transport apparatus 200 according to the first embodiment of the present invention.

<Details of intermediate transport section (transfer drum)>
FIG. 2 is an enlarged view of the recording medium transport apparatus 200 that is a main part of the ink jet recording apparatus 100 of the first embodiment, and further shows the recording medium transport apparatus 200 according to the first embodiment, particularly in the vicinity of the drawing drum 170. explain in detail.

  As shown in FIG. 2, in the recording medium conveyance device 200, the processing liquid drum 154, the intermediate conveyance unit 126 (first transfer cylinder), the drawing drum 170, the intermediate conveyance unit 128 (second transfer cylinder), the drying drum 176, the intermediate The conveyance unit 130 (third transfer cylinder) and the fixing drum 184 are arranged side by side, and the recording medium 124 is conveyed by the respective drums. During the conveyance, treatment liquid application, drawing, drying, and fixing (curing) are sequentially performed. To be done.

  Here, on the drawing drum 170, the sheet pressing roller 202 that presses the recording medium 124 in order to remove the wrinkles of the recording medium 124 conveyed by the drawing drum 170 on the upstream side of the inkjet head 172 in the conveying direction of the recording medium 124. Is provided.

On the outer peripheral surface of the drawing drum 170 between the paper pressing roller 202 and the inkjet head 172, as a special configuration according to the present embodiment, the amount of floating of the conveyed recording medium 124 from the drawing drum 170 is detected. The lift amount detection sensors 204 to be installed are installed at a plurality of locations (three locations in the present embodiment). The “lifting amount” is a general term including not only the floating of the recording medium 124 but also the rising due to the folding of the recording medium 124 or the adhesion of foreign matter. Further, as the “lifting amount”, the maximum value of the lifting amount at each position of the recording medium 124 detected by the lifting amount detection sensor 204 at any time can be used.
Further, the type of the lift amount detection sensor 204 is not particularly limited, and a general optical sensor 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, among the lift amount detection sensors 204, the lift amount detection sensor 204 on the most downstream side in the transport direction of the recording medium 124 has a distance D between the ink jet head 172 (particularly, the ink jet head 172M) and the paper transport braking distance. Is set longer than.

<Description of control system>
FIG. 3 is a principal block diagram showing the system configuration of the inkjet recording apparatus 100 according to the first embodiment of the present invention.

  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. 3, the motor (actuator) disposed in each part of the ink jet recording apparatus 100 is represented by reference numeral 98. For example, the motor 98 in FIG. 3 includes the 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 in FIG.

  As will be described in detail later, when the recording medium 124 is conveyed, paper floating or adhesion of foreign matter occurs, and the floating amount of the recording medium 124 increases and the recording medium 124 is transferred to the inkjet heads 172M, 172K, 172C, and 172Y. When there is a possibility of contact, 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. 3, a plurality of heaters provided in the inkjet recording apparatus 100 are represented by reference numeral 99. For example, the heater 99 shown in FIG. 3 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 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.

  The system control unit 82 is connected to the lifting amount detection sensor unit 20 and the head height control unit 30.

  The lift amount detection sensor unit 20 includes the above-described three lift amount detection sensors 204.

  The head height control unit 30 controls the relative position (height) of the inkjet head 172 relative to the surface of the recording medium 124 conveyed on the drawing drum 170. As will be described in detail later, for example, when paper floating occurs in the recording medium 124 being conveyed and the recording medium 124 is likely to come into contact with the inkjet head 172, the height of the inkjet head 172 relative to the drawing drum 170 is increased. Thus, control is performed so as to avoid contact. The specific configuration for changing the height of the inkjet head 172 is not particularly limited, and for example, a mechanical mechanism using a gear such as a pinion rack can be applied.

  The distance between the recording medium 124 and the inkjet head 172 is normally set to 1 mm. The inkjet head 172 is 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 possible to move up to 2 mm, and it is also possible to stop at an intermediate position of 2 mm. Here, the height of 3 mm is the maximum value at which the ink jet head 172 can rise onto the transport unit, and the height of 2 mm is a height at which ink droplets can be ejected from the ink jet head 172 toward the recording medium 124. It is the limit.

<Partial flow of system controller>
FIG. 4 is a flowchart showing an operation sequence related to the detection of the floating amount of the recording medium 124 and the subsequent processing in the image forming method of the present embodiment. Hereinafter, the operation sequence related to the detection of the floating amount of the recording medium 124 and the subsequent processing in the image forming method of the present embodiment will be described with reference to the flowchart of FIG. The following parentheses are step identification codes in the figure.

(S 100) 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, and on the drawing drum 170. After passing the paper pressing roller 202, the first lifting amount detection sensor 204 in the lifting amount detection sensor unit 20 detects the lifting amount of the recording medium 124. The lift amount is acquired by the system control unit 82. Hereinafter, the lift amount detected by the lift amount detection sensor 204 is referred to as a first lift amount.
(S102) The system control unit 82 determines whether or not the acquired first lifting amount is equal to or greater than the distance H _TD between the drawing drum 170 and the recording medium 124 set in advance. If a positive determination is made, the process proceeds to step S116, and if a negative determination is made, the process proceeds to step S104. Note that the preset distance H _TD between the drawing drum 170 and the recording medium 124 is, for example, a distance obtained by subtracting the thickness of the recording medium 124 from the distance between the drawing drum 170 and the inkjet head 172, 3/4 of the distance.

(S104) Similarly, the second lifting amount detection sensor 204 of the lifting amount detection sensor unit 20 detects the first lifting amount of the recording medium 124. Then, the first lifting amount is acquired by the system control unit 82.
(S106) The system control unit 82 determines whether or not the acquired first lifting amount is equal to or greater than the distance H _TD between the drawing drum 170 and the recording medium 124 set in advance. If a positive determination is made, the process proceeds to step S116, and if a negative determination is made, the process proceeds to step S108.

(S108) Similarly, the third lifting amount detection sensor 204 in the lifting amount detection sensor unit 20 detects the first lifting amount of the recording medium 124. Then, the first lifting amount is acquired by the system control unit 82.
(S110) The system control unit 82 determines whether or not the acquired first lifting amount is equal to or greater than the distance H _TD between the drawing drum 170 and the recording medium 124 set in advance. If the determination is affirmative, the process proceeds to step S116, and if the determination is negative, the process proceeds to step S112.

(S112) The system control unit 82 determines that the recording medium 124 is based on the correlation between the plurality of first lifting amounts detected by the lifting amount detection sensor unit 20 and the detection time after the recording medium 124 passes the paper pressing roller 202. A second lifting amount H _PRE at the time to reach the position facing the inkjet head 172 is predicted.
Specifically, a plurality of detection times (T) and first lifting amount (H) are extrapolated linearly from (T1, H1), (T2, H2), (T3, H3) (FIG. 5A). (See (C)), the second lifting amount H _PRE at the time when the recording medium 124 reaches the position facing the inkjet head 172 is predicted.

In addition, the first lifting amount at 200 milliseconds is linearly based on the three first lifting amounts obtained while the time after the recording medium 124 passes through the sheet pressing roller 202 is less than 200 milliseconds. The predicted first lifting amount may be predicted as the second lifting amount H _PRE . In this prediction method, the actual amount of time when the first lifting amount predicted at 200 milliseconds after the recording medium 124 passes through the paper pressing roller 202 reaches the position where the recording medium 124 faces the ink jet head 172 is used. Since it is based on the empirical rule that it is almost the same as the second lifting amount, the second lifting amount H _PRE is not excessively predicted.

In addition, a plurality of tables in which the relationship between the time after the recording medium 124 passes through the sheet pressing roller 202, the first lifting amount, and the second lifting amount are associated as data are stored in the EEPROM 85. Of the stored tables, the table having the closest data to the first lift amount detected by the lift amount detection sensor unit 20 is selected, and the table in the selected table is selected. You may output 2 lift amount _HPRE as a prediction result. In this prediction method, in order to predict the second lift amount _HPRE , each detected first lift amount and a table having the closest data are selected, and the second lift amount in the selected table is selected. Therefore, the prediction of the second lifting amount H _PRE is faster.

(S114) The system control unit 82 determines whether or not the second lifting amount H _PRE as a prediction result is equal to or greater than the distance H _TD between the drawing drum 170 and the recording medium 124 set in advance. If the determination is affirmative, the process proceeds to step S116, and if the determination is negative, the process ends.

  (S116) The system control unit 82 performs contact prevention control between the inkjet head 172 and the recording medium 124 before the recording medium 124 is conveyed to a position facing the inkjet head 172. Specifically, the system control unit 82 reduces the conveyance speed of the recording medium 124 via the motor driver 86, such as stopping the feeding and conveyance of the recording medium 124. Alternatively, the system control unit 82 may increase the height of the inkjet head 172 relative to the drawing drum 170 via the head height control unit 30.

<Effect>
As described above, according to the embodiment of the present invention, even if the recording medium 124 is lifted after passing through the most downstream lifting amount detection sensor 204 of the three lifting amount detection sensors 204, first, the system control unit 82. However, based on the plurality of first lifting amounts detected by each lifting amount detection sensor 204 when the recording medium 124 passes through each lifting amount detection sensor 204, the second lifting amount H _PRE at the position facing the inkjet head 172 is calculated. Predict. Then, before the recording medium 124 is transported to a position facing the ink jet head 172, based on the predicted second lifting amount _HPRE , the transport speed is reduced, such as by stopping the rotation of the drawing drum 170, or the ink jet head 172. Is retracted (increased) from the drawing drum 170, so that contact between the inkjet head 172 and the recording medium 124 can be prevented.

  Further, the distance D between the lift amount detection sensor 204 on the most downstream side in the conveyance direction of the recording medium 124 and the inkjet head 172 (particularly, the inkjet head 172M) is set to be longer than the braking distance of the sheet conveyance. Before the recording medium 124 is conveyed to a position facing the inkjet head 172, the conveyance speed of the drawing drum 170 is decreased or the inkjet head 172 is retracted from the drawing drum 170. Contact with the recording medium 124 can be reliably prevented.

In addition, since the lift amount detection sensors 204 are installed at a plurality of locations on the outer peripheral surface of the drawing drum 170 between the paper pressing roller 202 and the inkjet head 172, the recording medium 124 has passed the paper pressing roller 202. Even if the recording medium 124 is lifted later, the first lifting amount between the sheet pressing roller 202 and the inkjet head 172 can be detected. For this reason, the prediction of the second lifting amount H _{PRE in} the system control unit 82 is also accurate.

(Modification)
Although the present invention has been described in detail with respect to specific embodiments, the present invention is not limited to such embodiments, and various other embodiments are possible within the scope of the present invention. It will be apparent to those skilled in the art, and for example, the plurality of embodiments described above can be implemented in combination as appropriate. Moreover, you may combine the following modifications suitably.

  For example, although the case where there are three lifting amount detection sensors 204 has been described, there may be two, or four or more.

  In the above embodiment, a sheet (cut paper) is used as the recording medium 124. However, a configuration in which a continuous paper (roll paper) is cut into a necessary size and fed is also possible. Further, 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 connected to a suction unit that performs suction from the suction hole. In addition, although the treatment liquid coating apparatus 156 has exemplified the configuration to which the application method using the roller is applied, the present invention is not limited to this, and various methods such as a spray method and an ink jet method can be applied.

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

  Further, although the case where the inkjet head 172 has a configuration of CMYK standard colors (four colors) has been described, the combination of ink colors and the number of colors is not limited to the present embodiment, and light ink, dark ink may be used as necessary. Ink and special 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.

  In the above embodiment, an ink jet type image recording apparatus using water-based ink using water as a solvent has been described as an example. However, the liquid to be ejected is not limited to ink for image recording / character printing, etc. Any liquid that uses a solvent or a dispersion medium soaking into the medium can be applied to various discharge liquids. Further, the case where the drawing format is the droplet discharge method has been described, but a toner method or the like may be used from the viewpoint of preventing member destruction of a charging device, a laser beam (exposure) device, or the like.

  Further, the conveyance method of the inkjet recording apparatus 100 has been described with respect to the impression cylinder conveyance method, but may be a belt conveyance method.

  Moreover, although the system control part 82 demonstrated the case where the prediction means and control means of this invention were combined, the prediction means and control means may be comprised separately on a program.

30 Head height controller (control means)
82 System control unit (control means, prediction means)
86 Motor driver (control means)
100 Inkjet recording apparatus (image forming apparatus)
124 recording medium 170 drawing drum (conveying means, drawing)
172 Inkjet head (image forming means, droplet discharge head)
202 Paper pressing roller (paper pressing member)
204 Lifting amount detection sensor H _PRE second lifting amount

Claims (6)

Image forming means for forming an image on a recording medium;
A conveying unit that conveys the recording medium to a position facing the image forming unit;
A plurality of lifts that are arranged at different positions in the transport direction upstream of the image forming unit in the transport direction of the recording medium and detect a first lift amount from the transport unit when the recording medium passes. A quantity detection means;
Predicting means for predicting a second lift amount of the recording medium at a position facing the image forming means based on the first lift amount of the recording medium at the time of passage detected by the lift amount detection means;
Control means for lowering the conveying speed of the conveying means or retracting the image forming means from the conveying means based on the second lifting amount predicted by the predicting means;
An image forming apparatus comprising: The distance between the lift amount detection means on the most downstream side in the transport direction and the image forming means among the lift amount detection means is set to be longer than the braking distance for paper transport.
The image forming apparatus according to claim 1. The transport means is a drawing cylinder that rotates and transports the recording medium,
The image forming means is a droplet discharge head having a nozzle for discharging droplets,
Provided on the upstream side of the recording medium in the transport direction from the droplet discharge head, and includes a paper pressing member that presses the recording medium transported by the drawing cylinder,
The lifting amount detection means is disposed at a plurality of locations between the paper pressing member and the droplet discharge head.
The image forming apparatus according to claim 1. The predicting means determines whether the recording medium is the droplet discharge head based on a correlation between a plurality of first lifting amounts detected by the lifting amount detection means and detection times after the recording medium passes through the sheet pressing member. Predicting the second lifting amount in the time to reach the position opposite to
The control means controls the conveyance means to convey the recording medium when the second lifting amount predicted by the prediction means is equal to or greater than a preset distance between the conveyance means and the recording medium. Stop,
The image forming apparatus according to claim 3. The prediction means includes
Based on a plurality of first lifting amounts during the time after the recording medium passes through the sheet pressing member is less than 200 milliseconds, the first lifting amount at 200 milliseconds is predicted linearly, and this prediction is made. The first lifting amount is the second lifting amount,
The image forming apparatus according to claim 4. Storage means storing a plurality of tables in which the relationship between the time after the recording medium passes through the paper pressing member, the first lifting amount, and the second lifting amount is associated as data;
The prediction means selects a table having the closest data to each first lift amount when detected by the lift amount detection means from the tables stored in the storage means, Outputting the second lifting amount in the selected table to the control means;
The image forming apparatus according to claim 4.

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