JP4104512B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that includes a droplet discharge head and forms an image on a recording medium.

  Inkjet recording apparatuses used as various image forming apparatuses such as printers, facsimiles, copying machines, plotters, etc., form (record) images by mounting a droplet discharge head that discharges liquid recording liquid (ink) from fine nozzles. )

  By the way, as an ink jet recording apparatus, a serial type apparatus in which a droplet discharge head (ink jet head) is mounted on a carriage and a recording medium is conveyed in the sub scanning direction while moving the carriage in the main scanning direction to form an image. There is a line type that includes a so-called line head having a main scanning width and forms an image by conveying a recording medium in the sub-scanning direction.

  In any of these types of ink jet recording apparatuses, when a droplet discharged from the droplet discharge head lands on the recording medium, the recording medium is stopped and one line (width in the sub-scanning direction of the head) is reached. When the recording is completed, the recording medium is conveyed by a predetermined amount, and the recording of the next line is repeated to form an image.

In the conventional ink jet recording apparatus, for example, as shown in FIG. 10, the recording medium 501 on the paper feed tray 502 is separated and fed one by one by a paper feed roller 503, and a pair of paper feed unit conveyance rollers is provided. 504 is fed between the conveying roller 505 and the pressure roller 506, and droplets are ejected while conveying the recording medium 501 in the sub-scanning direction at a position facing the recording head 507 by the conveying roller 505. The recording medium 501 that is formed and on which an image is formed by the paper discharge transport roller 508 is configured to be sent out in the paper discharge direction.
JP-A-8-110660 JP 2001-260341 A

The conventional image recording apparatus includes a process unit that affects the physical properties of the recording medium on which an image is formed by the image recording unit, and is disposed between the image recording unit and the process unit. Some have loop forming means that bends in a loop shape.
JP 2000-203744 A

  In an image forming apparatus using a droplet discharge head, a droplet discharged from the droplet discharge head must be landed accurately at a predetermined position on the recording medium. At this time, sub-scanning of the recording medium is performed. When the transport accuracy (feed amount accuracy) of feed is lowered, it becomes impossible to land a droplet on a predetermined position, and image quality is lowered.

  However, in the conveyance mechanism in the conventional image forming apparatus as described above, when the recording medium is sub-scan fed by the conveyance roller, the sheet feeding roller is in contact with the recording medium or the sheet feeding is performed. For this reason, a load due to the rotation of the roller or the like due to the rotation of the roller or the back tension due to the bending load due to the recording medium itself due to the guide plate shape is applied to the sub-scan feed of the recording medium. Alternatively, when the recording medium passes through the paper feed unit conveyance roller, a force in the feeding direction may act on the recording medium due to the waist of the recording medium. In particular, with thick paper, the back tension increases due to the influence of bending load (friction load with the guide plate).

  Therefore, even if the sub-scanning motor that drives the conveyance roller is accurately driven and controlled, the tension applied to the recording medium varies (due to disturbance), so an error occurs in the actual feed amount of the recording medium, As a result, there is a problem that the image quality is degraded.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus that improves the image quality by increasing the sub-scan feed accuracy of the recording medium.

In order to solve the above problems, an image forming unit including a droplet discharge head that discharges droplets from a nozzle, a sub-scanning conveyance unit that conveys a recording medium in the sub-scanning direction so as to face the image forming unit, In an image forming apparatus comprising a paper feed transport means for transporting a recording medium fed to the sub-scan transport means, a recording medium in a transport path between the sub-scan transport means and the paper feed transport means The recording medium by the paper feeding / conveying means is provided so as to reduce the loop amount of the recording medium when the trailing end of the recording medium passes through the conveying roller of the paper feeding / conveying means. The feed amount is controlled.

  Further, it is preferable that a guide member that forms a conveyance path that bends the recording medium in a loop shape is provided so as to be able to swing in a direction of retreating from the conveyance path.

  In these image forming apparatuses, it is preferable that the driving source of the paper feeding / conveying means is a stepping motor, and it is preferable that an image reading means for reading an image is provided.

According to the image forming apparatus according to the present invention comprises means for forming a loop in the transport path between the sheet feed conveying unit and the sub-scanning conveyance means by bending the recording medium, the rear end portion of the recording medium Since the feed amount of the recording medium by the paper feeding / conveying means is controlled so that the loop amount of the recording medium becomes small when the roller passes through the conveyance roller of the paper feeding / conveying means, the back tension fluctuation applied to the recording medium The sub-scan feed accuracy is increased and the image quality is improved.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. An example of an image forming apparatus according to the present invention will be described with reference to FIGS. 1 is a schematic configuration diagram showing the overall configuration of the image forming apparatus, FIG. 2 is an explanatory plan view of an image forming unit and a sub-scanning conveying unit of the apparatus, and FIG. 3 is an explanatory diagram of a sub-scanning conveying unit of the apparatus. It is.

  This image forming apparatus has an image forming part (means) 2 for forming an image, a sub-scanning conveying part (means) 3, etc. in the inside (enclosure) of the apparatus main body 1. A recording medium (hereinafter referred to as “paper”, but not limited to paper) 5 is fed one by one from the provided paper feeding unit (means) 4, and the paper 5 is imaged by the sub-scanning conveyance unit 3. The image forming unit 2 ejects liquid droplets onto the paper 5 while forming (recording) it while conveying it at a position facing the forming unit 2, and then forms it on the upper surface of the apparatus main body 1 through the paper discharge conveying unit 6. The paper 5 is discharged onto the discharged paper discharge tray 7.

  This image forming apparatus also serves as an input system for image data (print data) to be formed by the image forming unit 2, and is an image reading unit (scanner) for reading an image above the discharge tray 7 above the apparatus body 1. Part) 11. The image reading unit 11 includes a scanning optical system 15 including an illumination light source 13 and a mirror 14 and a scanning optical system 18 including mirrors 16 and 17. The scanned document image is read as an image signal by the image reading element 20 disposed behind the lens 19, and the read image signal is digitized and subjected to image processing, and the image-processed print data is printed. be able to. A pressure plate 10 is provided on the contact glass 12 for pressing the document.

  Further, this image forming apparatus uses an information processing apparatus such as an external personal computer, an image reading apparatus such as an image scanner, and an imaging apparatus such as a digital camera as an input system for image data (print data) formed by the image forming unit 2. For example, print data including image data from the host side can be received via a cable or a network, and the received print data can be processed and printed.

  Here, as shown in FIG. 2, the image forming unit 2 of the image forming apparatus is guided by a carriage guide 21 and moved on a carriage 23 that can move in a main scanning direction (a direction perpendicular to the sheet conveying direction). A recording head 24 for ejecting droplets of different colors is mounted, the carriage 23 is moved in the main scanning direction, and the recording head 5 is fed in the paper transport direction (sub-scanning direction) by the sub-scan transport unit 3. 24 is a shuttle type in which droplets are ejected from 24 to form an image.

  The recording head 24 includes four liquid droplet ejection heads that eject black (Bk) ink, cyan (C) ink, magenta (M) ink, and yellow (Y) ink, respectively, and a sub tank 25 mounted on the carriage 23. Are supplied with ink of each color. Ink is replenished and supplied to each sub tank 25 from an ink cartridge 26 (FIG. 1) of each color which is a main tank detachably mounted in the apparatus main body 1 through a tube (not shown). In addition to the recording head 24 that discharges ink droplets, a recording head that discharges a fixing treatment liquid (fixing ink) that reacts with the recording liquid (ink) to improve the fixing property of the ink can be provided.

  The recording head 24 uses a piezoelectric element as a pressure generating means (actuator means) for pressurizing the ink in the ink flow path (pressure generation chamber) to deform the vibration plate that forms the wall surface of the ink flow path. A so-called piezo type that discharges ink drops by changing the volume in the flow path, or discharges ink drops with pressure generated by heating the ink in the ink flow path using a heating resistor to generate bubbles. The so-called thermal type, the diaphragm that forms the wall surface of the ink flow path and the electrode are placed opposite to each other, and the diaphragm is deformed by the electrostatic force generated between the vibration plate and the electrode, thereby the ink flow path inner volume It is possible to use an electrostatic type or the like that discharges ink droplets by changing the above.

  Although a plurality of recording heads are provided here, a configuration in which one or a plurality of recording heads having a plurality of nozzle rows that eject ink droplets of different colors may be provided. Although the serial type is used here, a line type using a full-line type head having a width in the main scanning direction can also be used. In this case, a plurality of line-type recording heads that discharge droplets of each color may be arranged in the sub-scanning direction, or one or a plurality of recording heads having a plurality of nozzle rows that discharge droplets of different colors Can be provided in such a manner that the nozzle rows are arranged in the sub-scanning direction.

  In addition, a maintenance / recovery mechanism (hereinafter referred to as “subsystem”) 27 including a head cleaning device for maintaining and recovering the state of the nozzles of the recording head 24 is provided in a non-printing area on one side in the scanning direction of the carriage 23. It is arranged. The subsystem 27 includes cap members 28a, 28b, 28c, and 28d for capping the nozzle surface of the recording head 24, a wiper blade 29 for wiping the nozzle surface, and the like.

  As shown in FIG. 3, the sub-scanning conveyance unit 3 is a driving roller for conveying the paper 5 fed from below by changing the conveyance direction by approximately 90 degrees and facing the image forming unit 2. An endless conveyance belt 31 laid between the conveyance roller 32 and the driven roller 33, a charging roller 34 to which a high voltage is applied from a high voltage power source (not shown) for charging the surface of the conveyance belt 31, and the conveyance belt 31 The image is formed by the guide member 35 that guides the sheet 5 in the opposite region of the image forming unit 2, the pressing roller 36 that presses the paper 5 against the conveying belt 31 at the position facing the conveying roller 32, and the image forming unit 2. A conveyance roller 37 for sending the formed paper 5 to the paper discharge conveyance unit 6 is provided.

  The conveyance belt 31 of the sub-scan conveyance unit 3 is rotated in the belt conveyance direction (sub-scanning direction) in FIG. 2 by rotating the conveyance roller 32 from the sub-scanning motor 131 via the timing belt 132 and the timing roller 133. It is configured to do.

  The transport belt 31 includes, for example, a surface layer that is a sheet adsorption surface formed of a pure resin material that is not subjected to resistance control, such as ETFE pure material, and a back layer that is subjected to resistance control using carbon with the same material as the surface layer. It has a two-layer structure (medium resistance layer, earth layer).

  Further, the configuration of the sub-scanning conveyance unit 3 is not limited to the conveyance belt. For example, as illustrated in FIG. 4, a printing that guides the conveyance roller (grinding roller) 38 and the paper 5 at a position facing the image forming unit 2. A configuration using the receiving member 39 can also be adopted.

  The paper feed unit 4 can be inserted into and removed from the apparatus main body 1, and a paper feed cassette 41 for stacking and storing a large number of papers 5 and a paper feed for separating and feeding the papers 5 in the paper feed cassette 41 one by one. A paper roller 42 and a friction pad 43, and a paper feed conveyance roller 44 that conveys the fed paper 5 to the sub-scanning conveyance unit 3 are provided.

  The paper feed roller 42 is rotated by a paper feed motor (drive source) 141 formed of an HB type stepping motor via a paper feed clutch (not shown), and the paper feed transport roller 44 is also rotationally driven by the paper feed motor 141. By using a stepping motor as the paper feed motor, synchronization control with the sub-scanning motor 131 is facilitated, and loop formation control is facilitated.

  The paper discharge conveyance unit 6 includes a pair of paper discharge conveyance rollers 61 and 62 for conveying the paper 5 on which image formation has been performed, a pair of paper discharge conveyance rollers 63 and a pair of paper discharge rollers for sending the paper 5 to the paper discharge tray 7. 64.

  In this image forming apparatus, as shown in FIGS. 1 and 5, the sheet 5 is bent by a conveyance path 91 extending from the sheet feeding conveyance roller 44 to the nip portion between the conveyance belt 31 and the pressing roller 36. Of the guide plates 92 and 93 for forming the loop 91, the outer guide plate 93 is provided so as to be swingable in the direction of the arrow. Accordingly, when the loop of the paper 5 is formed, the guide plate 93 can be swung in the direction of retreating from the conveyance path 91 by the bending load of the paper 5.

  Further, a loop sensor 95 that constitutes a detecting means for detecting the loop amount of the sheet 5 conveyed on the conveyance path 91 is provided in the vicinity of the exit of the sheet feeding conveyance roller 44. As the loop sensor 95, it is possible to employ a configuration that includes a filler that is displaced according to the loop amount of the paper 5, and detects the loop amount based on the displacement amount of the filler.

Next, an outline of the control unit of the image forming apparatus will be described with reference to FIG. The figure is a schematic block diagram of the control unit.
The control unit 100 includes a CPU 101 that controls the entire image forming apparatus, a ROM 102 that stores programs executed by the CPU 101 and other fixed data, a RAM 103 that temporarily stores image data (print data), and the like. Non-volatile memory (NVRAM) 104 for holding data even while the power is cut off, image processing for performing various signal processing and rearrangement on image data, and other input / output signals for controlling the entire apparatus An ASIC 105 for processing and a scanner control unit 106 for performing image reading by the image reading unit 11 and data processing of the read image are provided.

  The control unit also controls the drive of the external I / F 107 for transmitting and receiving data and signals used when receiving data from an external apparatus, and the recording head 24 of the image forming unit 2. And a motor driver for independently driving the main scanning motor 121, the sub-scanning motor 131, and the paper feed motor 141, which are driving sources for moving the carriage 23 in the main scanning direction. A motor driving unit 111, 112, 113 and a clutch driving unit 114 for turning on / off a paper feeding clutch 142 for transmitting the rotation of the paper feeding motor 141 to the paper feeding roller 42 are provided.

  The control unit further includes an I / O 115 for capturing the detection signals of the loop sensor 95 and various sensors (not shown), and an operation panel 116 for inputting and displaying information necessary for the apparatus. It is connected.

  Next, when the image reading unit 11 reads a document image, the control unit 100 processes the read image and stores it in a buffer in the scanner control unit 106. When print data or the like is received from an external host such as an information processing apparatus such as a personal computer, an image reading apparatus such as an image scanner, or an imaging apparatus such as a digital camera, etc., via the external I / F 107, the external I / F 107 is used. Is stored in the receive buffer included in.

  The CPU 101 reads out and analyzes the image data from the scanner control unit 106 and the external I / F 107, performs necessary image processing, data rearrangement processing, and the like in the ASIC 105, and sends the print image data to the head drive control unit 108. Forward. Note that the generation of dot pattern data for image output based on external data may be performed by storing font data in the ROM 102, for example, or image data is converted into bitmap data by a printer driver on the external host side. The image may be developed and transferred to the image forming apparatus.

  When the head drive control unit 108 receives image data (dot pattern data) corresponding to one row of each recording head 24, the head drive control unit 108 transfers the dot pattern data for one row to the head driver 109. Based on the pattern data, a drive waveform is selectively applied to the actuator means of the recording head 24 for driving. As a result, droplets are ejected from the required nozzles of each recording head 24.

  At this time, the paper 5 is transported one line at a time by the sub-scan transport unit 3 and stopped, and the recording head 24 is ejected while the main scanning is performed to record one line, thereby recording one line. When the processing is completed, a required image is formed on the paper 5 by repeatedly carrying (feeding) the paper 5 by one line by the sub-scanning conveyance unit 3.

Next, a sheet conveying operation in the image forming apparatus configured as described above will be described with reference to FIG.
First, the paper feed motor 141 is started to be driven at a predetermined feed amount, and the paper feed clutch 142 is turned on to feed the paper 5 stored in the paper feed cassette 41 one by one. The sheet is further conveyed by the sheet feeding conveyance roller 44 that is driven to rotate, and as shown by a solid line in FIG. 5, the sheet passes through the conveyance path 91 to the nip portion between the conveyance belt 31 of the sub-scanning conveyance unit 3 and the pressing roller 36. The paper 5 is conveyed until the tip of 5 reaches.

  At this time, by keeping the sub-scanning motor 131 in a stopped state (the sub-scanning motor 131 may or may not be driven in the previous stage), the conveyance belt 31 and the pressing roller 36 can be used. Since the sheet 5 having its tip abutted against the nip portion is further conveyed by receiving the conveying force by the sheet feeding and conveying roller 44, it bends (swells outward) as indicated by the broken line in FIG. 5a is formed. Even if the sub-scanning motor 131 is not stopped, the loop 5a is formed in the same manner as long as the feeding amount of the paper feeding conveyance by the paper feeding motor 141 is larger than the feeding amount of the sub-scanning conveyance by the sub-scanning motor 131. Become.

  When the feed amount of the sheet 5 reaches a predetermined amount, that is, when the sheet 5 is fed and transported by the feed amount that forms the loop 5a in the transport path 91 on the sheet 5, the sub-scanning motor 131 is driven. Thereafter, the sub-scanning motor 131 and the paper feed motor 141 are synchronously controlled, and the sub-scan feed and the paper feed conveyance are always performed with the feed amount in which the loop 5a of the paper 5 is maintained in the conveyance path 91. I do. In this case, when the paper 5 is intermittently fed by driving the sub-scanning motor 131, if the paper feed motor 141 is driven and fed by the sub-scan feed amount, the loop of the paper 5 in the transport path 91 is achieved. 5a is maintained.

  In this way, by forming a loop by bending the paper in the transport path between the sub-scan transport means and the paper feed transport means, the effect of back tension fluctuations on the paper is reduced, and the sub-scan feed accuracy is reduced. Increases the image quality.

  In this case, by performing synchronous control of sub-scan feed and paper feed transport after forming the initial loop, it is possible to prevent the loop amount from becoming zero, and feed control that maintains a good loop amount is possible. become. According to experiments, the initial loop amount is preferably 10 mm or less, particularly preferably 5 to 6 mm, based on the conveyance path 91. Therefore, by setting the initial loop amount within this range, it is possible to perform feeding while maintaining a good loop amount.

  In addition, by making the guide plate 93 on the outer side (the side on which the paper 5 swells) forming the conveyance path 91 swing freely, the guide plate 93 can be retracted when the loop amount of the paper 5 becomes too large. Thus, it is possible to prevent the force due to the increase in the loop amount from acting on the sub-scanning conveyance unit.

  Thereafter, when the trailing edge of the sheet 5 passes through the sheet feeding roller 44, the feeding amount of the sheet feeding motor 141 is reduced based on the detection result of the loop sensor 95, and the trailing edge of the sheet 5 is Control is performed so that the loop amount is minimized when the feed roller 44 passes through.

  In this way, the influence of the trailing edge of the sheet can be reduced by minimizing the loop amount when the trailing edge of the sheet passes through the paper feed roller. In other words, if the amount of loop when the paper passes through the paper feed conveyance roller is large, a force is applied to the sub-scanning conveyance section by the waist of the paper, and the sub-scan feed may become unstable. The amount is reduced to reduce this effect.

Next, synchronous control will be described with reference to FIG.
As described above, if the synchronous control of the sub-scan feed and the paper feed transport is performed after the initial loop is formed (drive control to make the feed amount the same), the initial loop amount is maintained as it is. In practice, however, there are various variations such as initial variations in the diameters of the transport roller 32 and the paper feed transport roller 44, variations due to environmental changes, and fluctuations in the frictional resistance between the paper 5 and the transport belt 31 and the paper feed transport rollers 44 due to environmental changes Depending on the factors, even if the driving amounts of the sub-scanning motor 131 and the paper feeding motor 141 are constant, the actual feed amount of the paper 5 may fluctuate.

  For this reason, the loop amount of the paper 5 also fluctuates due to fluctuations in the feed amount of the paper 5, and the loop amount becomes zero or becomes excessively large, so that a force acts on the sub-scanning conveying unit. Sometimes it is.

  Therefore, here, as shown in FIG. 8, the loop amount of the paper 5 is detected by the loop sensor 95, and when the loop amount decreases below the set amount, the feed amount of the paper feed motor 141 is increased to reduce the loop amount. Further, when the loop amount increases beyond the set amount, control is performed to decrease the loop amount by decreasing the feed amount of the paper feed motor 141.

  As a result, the sheet can be fed while stably maintaining a good loop amount, and the sheet can be conveyed stably with high sub-scan feed accuracy.

Next, the feed amount setting process of the paper feed motor will be described with reference to FIG.
As the paper 5, there are papers that are stiff and papers that are weak. If a large loop is formed on a stiff sheet, the sub-scanning conveyance section tends to be pushed, and a friction load or back tension may be generated. Therefore, here, by setting the feed amount of the paper feed motor 141 according to the thickness of the paper 5, the friction load and the back tension due to the stiffness of the paper are reduced.

  In other words, parameters of the paper type (thickness) and the feed amount of the paper feed motor are stored in the ROM 102 of the control unit 100, and the designation means for designating the paper type (thickness) on the operation panel 116. (Designated by switch or menu selection).

  When the drive control of the paper feed motor 141 is performed, a set feed amount corresponding to the designated sheet thickness is read out, and based on the read feed amount (second feed amount <first feed amount). The feed control of the paper 5 by the paper feed motor 141 is performed.

  In the above-described embodiment, the present invention has been described with reference to an example in which the present invention is applied to a multifunction (MFP) image forming apparatus. However, the present invention can be similarly applied to other image forming apparatuses such as a printer and a facsimile apparatus.

1 is a schematic configuration diagram illustrating an overall configuration of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is an explanatory plan view of an image forming unit of the image forming apparatus. FIG. 3 is an enlarged explanatory diagram of a sub-scanning conveyance unit in the image forming apparatus. FIG. 6 is an enlarged explanatory view for explaining another configuration of the sub-scanning conveyance section. FIG. 6 is an enlarged explanatory view of a portion from a sheet feeding conveyance roller to a conveyance belt. 2 is a block for explaining an outline of a control unit of the image forming apparatus. FIG. 6 is a flowchart for explaining the operation of the image forming apparatus. It is a flowchart with which an operation | movement description is similarly provided. It is a flowchart with which an operation | movement description is similarly provided. FIG. 10 is an explanatory diagram of a main part for explaining a conventional image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Apparatus main body 2 ... Image formation part 3 ... Sub-scanning conveyance part 4 ... Paper feed part 5 ... Paper (recording medium)
6 ... Discharge conveying unit 7 ... Discharging tray 11 ... Image reading unit 23 ... Carriage 24 ... Recording head 31 ... Conveying belt 41 ... Feeding roller 44 ... Feeding conveying roller 91 ... Conveying paths 92, 93 ... Guide plate 95 ... Loop sensor 131 ... sub-scanning motor 141 ... feed motor

Claims (4)

An image forming unit including a droplet discharge head for discharging droplets from a nozzle, a sub-scanning conveying unit that conveys a recording medium in the sub-scanning direction so as to face the image forming unit, and the sub-scanning conveying unit In an image forming apparatus comprising: a paper feeding / conveying unit that conveys the fed recording medium,
Means for bending the recording medium in a conveyance path between the sub-scanning conveyance means and the paper feed conveyance means to form a loop;
Controlling the feeding amount of the recording medium by the paper feeding / conveying means so that the loop amount of the recording medium becomes small when the rear end of the recording medium passes through the conveyance roller of the paper feeding / conveying means. An image forming apparatus. The image forming apparatus according to claim 1 , wherein a guide member that forms a conveyance path for bending the recording medium in a loop shape is provided so as to be swingable in a direction of retreating from the conveyance path. Forming equipment. 3. The image forming apparatus according to claim 1 , wherein a driving source of the paper feeding / conveying means is a stepping motor. The image forming apparatus according to any one of claims 1 to 3, the image forming apparatus characterized by comprising an image reading means for reading an image.

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