JP2005132538A - Paper carrying device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem in a conventional paper carrying device wherein, when high voltage is supplied, through a bearing, to a charging roller for charging a carrying belt for carrying a paper sheet by electrostatic attraction, resistance variation becomes large and changing for the electrostatic attraction cannot be stably performed. <P>SOLUTION: This paper carrying device comprises a first power supply passage supplying high voltage from a high-voltage power supply 265 to the peripheral surface of the shaft part of the charging roller 26 through a bearing pressurizing spring 264 and the conductive bearing 262 and a second power supply passage supplying high voltage from the high-voltage power supply 265 to the shaft end face of the shaft part of the charging roller 26 through the bearing pressurizing spring 264 and a high-voltage supply plate spring 268 and without passing through the conductive bearing 262. A current flowing through the second power supply passage is formed larger than a current flowing through the first power supply passage. The power supply passage passed through the bearing is used as a secondary one. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus, and more particularly to a sheet conveying apparatus and an image forming apparatus that convey a sheet by electrostatically attracting a sheet to a conveying belt.

  As various image forming apparatuses such as printers, facsimiles, copiers, plotters, printer / facsimile / copier multifunction machines, etc., a liquid droplet ejecting head for ejecting a recording liquid is provided as a recording head, and the liquid droplets ejected from the recording head Means paper (not limited to paper but includes OHP, etc., and can be attached to ink droplets, developer, and other recording liquids, and is also called a recording medium, recording medium, recording paper, or the like. ) Is formed to form an image.

  By the way, in such an image forming apparatus, at least paper is transported intermittently in the sub-scanning direction, the paper is stopped and scanned in the main scanning direction, or one line (sub-scanning direction). The image is formed by repeating the recording for the nozzle row width). Therefore, in order to improve the image quality, it is necessary to feed the paper with high accuracy.

  In addition, since the liquid droplets land on the paper to form an image, it is necessary to improve the flatness of the paper. However, when printing on plain paper, the paper fibers swell due to moisture contained in the recording liquid. As a result, the liquid droplet is deformed into a wave shape, and the landing position of the droplet is displaced.

  Therefore, in order to maintain the flatness of the paper, an endless charging belt (referred to as a conveyance belt) is provided, the surface of the conveyance belt is charged to electrostatically adsorb the paper, and the conveyance belt is circulated in this state. 2. Description of the Related Art There is known an image forming apparatus that can maintain high flatness by preventing a sheet from being lifted from a conveyor belt by conveying a sheet.

  Incidentally, in order to charge the transport belt in this way, a contact charging device that charges the transport belt by applying a high voltage to a charging roller that contacts the transport belt is generally used. In order to perform accurate and stable paper feeding, charging by the charging roller needs to be performed stably, and high-voltage power supply to the charging roller must also be performed stably.

Conventionally, as a power supply device that supplies power to a contact charging device that charges an image carrier such as a photoconductor, there is a device disclosed in Patent Document 1. This power supply device includes a power supply path for supplying power to a charging roller from a high-voltage power supply, a path for supplying power to a shaft portion including the rotating shaft via a bearing that receives the rotating shaft of the charging roller, and a bearing that receives the rotating shaft of the charging roller. And a path for supplying power directly to the shaft portion including the rotating shaft without going through the shaft.
Japanese Patent Laid-Open No. 10-104912

Similarly, a contact charging device that charges an image carrier such as a photoconductor is disclosed in Patent Document 2. Similarly to the power supply device of Patent Document 1, this contact charging device also includes a shaft including a rotation shaft via an outer peripheral surface of a bearing that receives the rotation shaft of the charging roller as a power supply path for supplying power to the charging roller from a high-voltage power supply. And a path for supplying power directly to the outer peripheral surface of the shaft portion including the rotary shaft without passing through the outer peripheral surface of the bearing that receives the rotary shaft of the charging roller.
JP-A-11-207185

  Both the above-described conventional power supply device and contact charging device can secure power supply from the other power supply path even if one power supply path is troubled by securing two power supply paths to the charging roller. I am doing so.

  By the way, the bearing of the charging roller is preferably made of a resin having conductivity from the viewpoint of ensuring slidability and cost, but the resin having conductivity has an unstable resistance value and varies. Large, the resistance fluctuation becomes large at the time of power feeding at the sliding portion, and radio noise is easily generated.

  Therefore, as in the prior art that intends to charge the image carrier, if two power supply paths are secured for the charging roller and power is supplied in the same way for both systems, the power supply via the bearings When the power supply fluctuation increases and the voltage fluctuation of the high voltage applied to the charging roller increases, and when the conveyance belt of the paper conveyance device is charged, a uniform charge cannot be formed on the conveyance belt. There is a problem that the sheet adsorbing force cannot be obtained and the sheet cannot be conveyed stably with high accuracy.

  The present invention has been made in view of the above problems, and a sheet conveying apparatus capable of stably conveying a sheet with high accuracy and an image forming apparatus capable of forming a high-quality image by including the sheet conveying apparatus. The purpose is to provide.

  A sheet conveying apparatus according to the present invention includes a first power supply path that supplies a high voltage for charging via a bearing made of a conductive resin that supports a rotating shaft of a charging roller for charging a conveying belt, and the bearing. And a second power supply path that supplies a high voltage for charging to the rotating shaft of the charging roller, and the current flowing through the second power supply path is higher than the current flowing through the first power supply path when supplying a high voltage to the charging roller. It has a large configuration.

  Here, the second power supply path includes a high-pressure supply leaf spring that is slidably in contact with the end surface of the rotating shaft of the charging roller, and the high-pressure supply leaf spring is held on the outer peripheral surface of the bearing. preferable. The high-pressure supply leaf spring is preferably pressed against the end surface of the rotating shaft of the charging roller by a spring force. Further, it is preferable that the contact width of the high-pressure supply leaf spring with the end surface of the rotating shaft of the charging roller is narrower than the width of the slit formed in the bearing.

  The image forming apparatus according to the present invention includes the sheet conveying apparatus according to the present invention as a sheet conveying apparatus that conveys a sheet on which an image is formed with recording liquid droplets discharged from a recording head.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall explanatory view showing an example of an image forming apparatus according to the present invention including a paper conveying apparatus according to the present invention, and FIG.
This image forming apparatus is an ink jet recording apparatus, and holds a carriage 3 slidably in a main scanning direction by a guide rod 1 and a guide rail 2 which are guide members horizontally mounted on left and right side plates (not shown). The scanning motor 4 moves and scans in the direction indicated by the arrow (main scanning direction) in FIG.

  The carriage 3 is provided with a recording head 7 composed of at least four ink jet heads for discharging recording liquid droplets of a plurality of colors such as cyan (C), magenta (M), yellow (Y), and black (K). The ink droplet ejection direction is directed downward.

  As an ink jet head constituting the recording head 7, a piezoelectric actuator such as a piezoelectric element, a thermal actuator that utilizes a phase change caused by film boiling of a liquid using an electrothermal transducer such as a heating resistor, and a metal phase change caused by a temperature change. A shape memory alloy actuator to be used, an electrostatic actuator using an electrostatic force, or the like as an energy generating means for discharging ink can be used.

  Here, a plurality of recording heads for ejecting droplets of each color are mounted on the carriage 3, but one or a plurality of recording heads having a plurality of nozzle rows for ejecting droplets of each color. 7 may be provided.

  Further, the carriage 3 is equipped with a sub tank 8 for each color for supplying the recording head 7 with ink as a recording liquid for each color. Ink is supplied to the sub tank 8 from a main tank (ink cartridge) via an ink supply tube (not shown).

  On the other hand, as a paper feed unit for feeding paper 12 stacked on a paper stacking unit (pressure plate) 11 such as a paper feed tray 10, a half-moon roller (for separating and feeding the paper 12 one by one from the paper stacking unit 11) A separation pad 14 made of a material having a large friction coefficient is provided facing the sheet feeding roller 13 and the sheet feeding roller 13, and the separation pad 14 is urged toward the sheet feeding roller 13 side.

  As a transport unit for transporting the paper 12 fed from the paper feed unit on the lower side of the recording head 7, a transport belt 21 for transporting the paper 12 by electrostatic adsorption, and a paper feed unit A counter roller 22 for transporting the paper 12 fed through the guide 15 between the transport belt 21 and the paper 12 fed substantially vertically upward is turned approximately 90 ° and copied onto the transport belt 21. A conveying guide 23 for adjusting the pressure and a tip pressing roller 25 urged toward the conveying belt 21 by a pressing member 24. In addition, a charging roller 26 as a charging unit for charging the surface of the transport belt 21 is provided.

  Here, the conveyance belt 21 is an endless belt, is stretched between the conveyance roller 27 and the tension roller 28, and the conveyance roller 27 rotates from the sub-scanning motor 31 via the timing belt 32 and the timing roller 33. By doing so, it is configured to circulate in the direction indicated by the arrow in FIG. 2 (belt (paper) conveyance direction: sub-scanning direction).

  This transport belt 21 is a surface layer that is a sheet adsorbing surface formed of a resin material having a pure thickness of about 40 μm that is not subjected to resistance control, for example, ETFE pure material, and resistance control by carbon is performed using the same material as the surface layer. It has a back layer (medium resistance layer, ground layer).

  Further, the conveyance roller nip portion 18 is formed by the conveyance roller 27 and the counter roller 22, and the sheet detection sensor 16 that detects the sheet 12 is disposed at a predetermined position upstream of the conveyance roller nip portion 18 in the sheet conveyance direction. . The paper detection sensor 16 detects the paper 12 by displacing the detection lever 17 by the paper 12 (the position indicated by the broken line in FIG. 1 is the ON position).

  The charging roller 26 is disposed so as to contact the surface layer of the conveyor belt 21 and rotate following the rotation of the conveyor belt 21, and applies 2.5N to both ends of the shaft as a pressing force. A configuration for supplying power to the transport roller 26 will be described later. Further, the transport roller 27 also serves as an earth roller, and is placed in contact with the middle resistance layer (back layer) of the transport belt 21 and is grounded.

  In addition, a guide member 36 is disposed on the back side of the conveyance belt 21 so as to correspond to a printing area by the recording head 7. The upper surface of the guide member 36 protrudes toward the recording head 7 from the tangent line of the two rollers (the conveyance roller 27 and the tension roller 28) that support the conveyance belt 21. As a result, the conveying belt 21 is pushed up and guided on the upper surface of the guide member 36 in the printing region.

  Further, as shown in FIG. 1, an encoder scale 42 having slits or lines is provided on the front side of the carriage 3, and a transmission type photosensor that detects the slits or lines of the encoder scale 42 on the front side of the carriage 3. An encoder 44 for detecting the position of the carriage 3 in the main scanning direction (position with respect to the home position) is configured.

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

  A double-sided paper feeding unit 61 is detachably mounted on the back. The double-sided paper feeding unit 61 takes in the paper 12 returned by the reverse rotation of the transport belt 21, reverses it, and feeds it again between the counter roller 22 and the transport belt 21.

  Further, although not shown, a maintenance / recovery mechanism for maintaining and recovering the nozzle state of the recording head 7 is disposed in the non-printing area on both sides in the scanning direction of the carriage 3. The maintenance / recovery mechanism includes a cap member for capping the nozzle surface of the recording head 3 and a wiper blade for wiping the nozzle surface.

  In the ink jet recording apparatus configured as described above, the paper 12 is separated and fed one by one from the paper feed unit, and the paper 12 fed substantially vertically upward is guided by the guide 15, and includes the transport belt 21 and the counter roller 22. The leading end is guided by the conveying guide 23 and pressed against the conveying belt 21 by the leading end pressing roller 25, and the conveying direction is changed by approximately 90 °.

  At this time, a positive output and a negative output are alternately repeated from the high voltage power source to the charging roller 26 by a control circuit (not shown), that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 21 is alternating, that is, In the sub-scanning direction, which is the circumferential direction, plus and minus are alternately charged in a band shape with a predetermined width. When the paper 12 is fed onto the conveyance belt 21 charged alternately with plus and minus, the paper 12 is electrostatically attracted to the conveyance belt 21, and the paper 12 is moved in the sub-scanning direction by the circular movement of the conveyance belt 21. Be transported.

  Therefore, by driving the recording head 7 according to the image signal while moving the carriage 3, the ink droplets are ejected onto the stopped paper 12 to record one line, and after the paper 12 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 12 has reached the recording area, the recording operation is finished and the paper 12 is discharged onto the paper discharge tray 54.

  In the case of double-sided printing, when recording on the front surface (surface to be printed first) is completed, the recording belt 12 is fed into the double-sided paper feeding unit 61 by rotating the conveyor belt 21 in the reverse direction. The paper 12 is reversed (with the back surface being the printing surface), fed again between the counter roller 22 and the transport belt 21, controlled in timing, and transported onto the transport bell 21 as described above. Then, after recording on the back surface, the paper is discharged onto the paper discharge tray 54.

  Therefore, a configuration for applying a high voltage to the charging belt constituting the paper conveying device in the image forming apparatus will be described with reference to FIGS. 3 is an explanatory view of the conveyor belt as viewed from the side, FIG. 4 is an explanatory view of the conveyor belt as viewed from the front, and FIG. 5 is an enlarged explanatory view of the main part of FIG.

  Shaft portions 261 and 261 at both ends of the charging roller 26 are rotatably supported by bearings 262 and 262, respectively, and bearings for pressing the charging roller 26 toward the conveying belt 21 between the bearings 262 and the fixing portion 263. Pressure springs 264 and 264 are interposed. Here, the bearing 262 on at least one side (the side that is electrically connected to the high-voltage power supply) is a bearing formed of a conductive resin, and the bearing 262 and the bearing pressure spring 264 are electrically connected. .

  The output side of the high-voltage power supply 265 for applying a high voltage to the charging roller 26 is connected to the relay member 267 via the high-voltage supply cable 266, and one bearing pressure spring 264 is connected to the relay member 267. Yes. As a result, a first power supply path is configured to supply high pressure from the high-voltage power supply 265 to the peripheral surface of the shaft portion 262 of the charging roller 26 via the bearing pressure spring 264 and the conductive bearing 262.

  Further, a conductive high-pressure supply leaf spring 268 that slidably contacts the end face (shaft end face) of the shaft portion 262 of the charging roller 26 from the axial opening of the bearing 262 is held on the outer peripheral portion of the bearing 262. It is pressed against the shaft end surface of the shaft portion 262 of the charging roller 26 by a spring force. The high pressure supply leaf spring 268 is electrically connected to the bearing pressure spring 264. As a result, the high-voltage power supply 265 supplies the high pressure to the shaft end surface of the shaft portion 262 of the charging roller 26 via the bearing pressure spring 264 and the high-pressure supply leaf spring 268 without passing through the conductive bearing 262. Is configured. Instead of the high-pressure supply leaf spring 268, a brush that contacts the shaft portion 262, a metal wire, or the like may be used.

  Here, a member that forms the high-pressure supply leaf spring 268 so that the resistance value of the second power supply path via the high-pressure supply leaf spring 268 is smaller than the resistance value of the first power supply path via the bearing 262, and The contact resistance with the shaft end face is set. The contact portion 269 that contacts the shaft end surface of the shaft portion 262 of the charging roller 26 of the high-pressure supply leaf spring 268 is configured to contact the shaft end surface by at least line contact, and the width of the contact portion 269 is formed in the bearing 262. The width is narrower than that of the slit 270.

  As shown in FIG. 4, the contact member 271 is pressed by a spring force on the shaft portion 271 of the transport roller 27 corresponding to the shaft portion 261 opposite to the shaft portion 261 that supplies the high pressure of the charging roller 26. The contact member 271 is connected to the ground to be the ground member for the transport roller 27.

  With this configuration, the high voltage output from the high voltage power supply 265 is transmitted from the outer peripheral surface or the shaft end surface of the shaft portion 261 of the charging roller 26 to the charging roller 26 via the first power supply path and the second power supply path. Supplied. At this time, since the resistance value of the second feeding path is made smaller than that of the first feeding path, the current flowing through the second feeding path is larger than the current flowing through the first feeding path. growing.

  That is, in this apparatus, a high voltage is supplied to the charging roller 26 via the first and second power supply paths, but the second power supply path not via the bearing 262 becomes the main power supply path, and the first power supply via the bearing 262 is the first power supply path. The power supply path is a subordinate power supply path, and has two power supply paths having a master-slave relationship. When a factor such as an increase in the contact resistance of the high-pressure supply leaf spring 268 occurs with time, power is supplied to the charging roller 26 complementarily from the first power supply path.

  Accordingly, a bearing made of a resin having conductivity is used as the bearing 262, and the resistance of the bearing made of the resin having conductivity is low while ensuring the slidability with the charging roller 26 using a bearing made of a resin having conductivity. When the resistance value of the power supply path without a bearing increases, avoiding the inconvenience of stable and large variation, large fluctuations in resistance when power is supplied at the sliding part, and easy generation of radio noise. In addition, power can be supplied via the bearing.

  As a result, instability caused by power feeding through a bearing made of a conductive resin can be prevented, so that the conveyance belt can be stably charged and the sheet conveyed by the conveyance belt can be stably electrostatically attracted. It can be conveyed by force, and the paper feeding accuracy is improved and the image quality is improved.

  The present invention can be applied to an image forming apparatus such as a printer, a facsimile machine, a copying machine, a printer / fax / copier multifunction machine, or an image forming apparatus using a recording liquid which is a liquid other than ink. Can also be applied. Furthermore, the present invention can also be applied to a paper transport device for transporting paper other than the image forming apparatus (the paper in this case means, for example, a document).

1 is a configuration diagram showing an outline of a mechanism part of an image forming apparatus according to the present invention. It is principal part plane explanatory drawing of the mechanism part. FIG. 3 is an explanatory side view illustrating a configuration for applying a high voltage to a charging belt that constitutes a sheet conveying device in the image forming apparatus. It is front explanatory drawing similarly. Similarly, it is a principal part expansion explanatory drawing of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Carriage 7 ... Recording head 21 ... Conveyance belt 26 ... Charging roller 27 ... Conveyance roller 261 ... Shaft part 262 ... Bearing 264 ... Bearing pressure spring 265 ... High voltage power supply 268 ... Plate spring for high voltage supply

Claims (5)

  In a sheet conveying apparatus that conveys a sheet by charging a surface of an endless conveying belt with a charging roller, a first charging voltage is supplied via a bearing made of a conductive resin that supports a rotating shaft of the charging roller. A current flowing through the second power supply path when a high voltage is supplied to the charging roller, the second power supply path supplying a high voltage for charging to the rotating shaft of the charging roller without passing through the bearing; Is larger than the current flowing through the first power supply path.   2. The sheet conveying device according to claim 1, wherein the second power supply path includes a high-pressure supply leaf spring that slidably contacts an end surface of the rotation shaft of the charging roller, and the high-pressure supply leaf spring is A paper conveying device, which is held on an outer peripheral surface of a bearing.   3. The paper conveying apparatus according to claim 2, wherein the high-pressure supply leaf spring is pressed against an end surface of a rotating shaft of the charging roller by a spring force.   4. The sheet conveying device according to claim 2, wherein a contact width of the high-pressure supply leaf spring with an end surface of a rotating shaft of the charging roller is narrower than a width of a slit formed in the bearing. Paper transport device. An image forming apparatus that includes a sheet conveying device that charges a surface of an endless conveying belt and conveys a sheet, and forms an image by ejecting droplets from a droplet ejection head onto the sheet. An image forming apparatus, which is the sheet conveying apparatus according to any one of 1 to 4.

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