JP4452309B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that conveys a sheet using a conveyance belt.

  As an image forming apparatus (or image recording apparatus) such as a printer, a facsimile machine, and a copying apparatus, for example, an ink jet recording apparatus is known. An ink jet recording apparatus means a sheet (not limited to paper but including OHP, which can be attached with ink droplets, developer, etc.) from an ink recording head. Recording is performed by discharging ink, and high-definition images can be recorded at high speed, running costs are low, noise is low, and multi-color ink is used. There are advantages such as easy recording of color images.

  As an inkjet head, a piezoelectric actuator such as a piezoelectric element, a thermal actuator that uses a phase change due to liquid film boiling using an electrothermal transducer such as a heating resistor, a shape memory alloy actuator that uses a metal phase change due to a temperature change, 2. Description of the Related Art An electrostatic actuator using an electrostatic force or the like is known as an energy generating unit for ejecting ink.

  By the way, in the ink jet recording method, when an image is formed in order to make ink adhere to the paper, there is a phenomenon that the paper is stretched by moisture contained in the ink. This phenomenon is called cockling. The cockling causes the paper to wave, and the positions of the nozzles of the head and the surface of the paper change from place to place. If the degree of cockling deteriorates, in the worst case, the paper will come into contact with the nozzle surface of the head, and the nozzle surface of the head may become dirty, or the paper itself may become dirty, resulting in a decrease in image quality. The impact position of the ink droplet may be shifted due to the influence.

  Therefore, in an ink jet recording apparatus, printing is performed on a platen provided with a recess that absorbs paper cockling, and a spur having a protrusion on the circumference is provided as a presser for the paper. What happens is also a problem.

  Further, in the conventional ink jet recording apparatus, paper is fed by rollers, and two sets of rollers (one is a combination of a spur and a roller as described above) are arranged across a printing area. However, with this configuration, the sheet feeding accuracy can be guaranteed only when the sheet is engaged with the two sets of rollers.

  However, in recent years, since it is desired to increase the image printing area, it is impossible to guarantee the sheet feeding accuracy in order to secure the printing area, that is, one of the two pairs of rollers. However, there is also an ink jet recording apparatus that performs printing in a state where the paper is not bitten. However, in the state where the paper bites only one of the roller pairs, if the paper floats, it is impossible to cope with it, and because the paper conveyance force cannot be secured, the feeding accuracy cannot be guaranteed, so the image quality is also deteriorated. Problem arises.

  Pursuing high image quality in an inkjet recording device requires accuracy of the landing position of ink droplets on the paper, and it is necessary to improve the flatness of the paper, but as described above, when printing on plain paper In other words, the moisture contained in the ink causes the paper fibers to swell and deform into a wave shape, resulting in a shift in the dot landing position. So far, it has been found that it takes about 3 seconds or more after the ink adheres to the paper to cause a large deformation of the paper.

Therefore, as described in Patent Document 1 and Patent Document 2, in order to maintain the flatness of the paper, an endless charging belt is provided, and the surface of the charging belt is charged to electrostatically adsorb the paper. Ink jet recording apparatuses have been proposed in which a sheet is conveyed by rotating the charging belt in a state to prevent the sheet from being lifted from the charging belt and maintain high flatness.

Japanese Patent No. 2897960 JP-A-7-53081

  Here, Patent Document 1 discloses a sheet conveying device and an image recording device in which a voltage applying unit is brought into contact with the surface of the charging belt and an alternating charge pattern is formed on the surface of the charging belt, for example, in a belt shape. Further, Patent Document 2 discloses a printing apparatus in which the potential on the charging belt is neutralized with a neutralizing brush in order to obtain a stable potential on the charging belt at all times.

If case of transporting the sheet by the charging belt (conveyor belt) As described above, the charging belt Ru adopted a structure to be stretched between at least two rollers, but which thus support the belt by two or more axes of the rollers, There is a problem in that slip occurs between the conveyance belt and a driving roller that drives the conveyance belt, and the feeding accuracy of the conveyance belt is lowered, resulting in a decrease in image quality.

  Further, there is a problem that the suction force due to the electrostatic suction force cannot be efficiently obtained because the transport paper is lifted from the transport belt. Further, when a roller or the like is used to press the paper against the conveyance belt, pressing by the roller becomes a driving load of the conveyance belt, and there is a problem that the image quality is degraded due to a decrease in accuracy of the conveyance belt at the stop position.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of forming a high-quality image by stably transporting paper.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
In an image forming apparatus that adsorbs and conveys a sheet on the surface of a conveying belt and forms an image on the sheet by an image forming unit.
Span the conveyor belt between at least two rollers;
Belt guide means for guiding the conveying belt from the inside at a position facing the image forming means is provided so that a guide surface protrudes from a tangent line of the two rollers;
The apparatus has a conveyance guide unit that guides the sheet that is sucked and conveyed by the conveyance belt from a position before the image forming unit and the conveyance belt are substantially parallel to a position that is substantially parallel .

  Here, the conveyance guide means may have a roller which is pressed and held on the conveyance belt side so as to face the roller on the upstream side in the conveyance direction and presses the paper. In this case, the roller provided in the conveyance guide means is movable in the pressurizing direction, is rotatably held by the conveyance guide means, and is provided with a pressure means that pressurizes a shaft that supports the roller. The guide means may be configured to be fixed with respect to the main body. Further, at least the surface of the roller provided in the conveyance guide means is formed of an elastic material, and the elastic material is formed of an elastomer, rubber, or an elastic resin, and at least the elasticity thereof is softer than the elasticity of the conveying belt that abuts. it can.

  Further, the conveyance guide means may be configured not to contact the belt guide means via the conveyance belt. In this case, a second roller is rotatably provided at the most downstream portion in the transport direction of the transport guide means, and the belt guide means has a position corresponding to the second roller and the inside of the transport belt. It can be set as the structure in which the escape part which does not contact was formed.

  The image forming apparatus according to claim 6, wherein at least two ribs are formed on a guide surface of the belt guide unit in a direction orthogonal to a sheet conveyance direction, and a space between the ribs serves as the relief portion. And can. In this case, at least one rib of the belt guide means may have a width of 5 mm or less. Further, the second roller can be configured to be able to press the paper to be conveyed against the conveying belt side.

  In addition, the roller on the upstream side in the paper conveyance direction can be a driving roller. In this case, the drive roller can be configured to have a larger diameter than other rollers. The drive roller may be configured to have a larger coefficient of friction with the inner surface of the transport belt than the other rollers. Further, the conveyance guide means may be configured to be fixed to the apparatus main body member so that the height position thereof can be adjusted with respect to the conveyance belt.

According to the image forming apparatus of the present invention, the guide surface of the belt guide unit that guides the conveyor belt from the inside at a position facing the image forming unit is provided between the at least two rollers. provided so as to protrude from the sheet being transported by the conveyor belt, the conveyor belt and the roller in the upstream side of the image forming means is substantially and the conveyed image forming means from a position facing the belt parallel front Since the conveyance guide means for guiding from the position to the position substantially parallel is provided , the sheet can be conveyed stably and the image quality is improved.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. A first embodiment of an image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram for explaining the overall configuration of the apparatus, and FIG. 2 is a plan view for explaining a main part of the apparatus.

  An ink jet recording apparatus, which is an image forming apparatus, holds a carriage 3 slidably in a main scanning direction by a guide rod 1 that is a guide member horizontally mounted on left and right side plates (not shown) and a stay (not shown). 7 (FIG. 2) is moved and scanned in the direction of the arrow in FIG. 2 via the timing belt.

  The carriage 3 includes a plurality of recording heads 4 that are image forming units including four inkjet heads that eject ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (Bk). Are arranged in a direction crossing the main scanning direction, and the ink droplet ejection direction is directed downward.

  As the ink jet head constituting the recording head 4, a piezoelectric actuator such as a piezoelectric element, a thermal actuator that uses 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.

  In addition, the carriage 3 is mounted with replaceable sub tanks 5 for each color for supplying ink of each color to the recording head 4. Ink is supplied to the sub tank 5 from a main tank (ink cartridge) (not shown) via an ink supply tube 6.

  On the other hand, as a paper feeding unit for feeding the paper 12 loaded on the paper stacking unit 11 such as a paper feed tray, a half-moon roller (paper feeding roller) 13 that separates and feeds the paper 12 from the paper stacking unit 11 one by one. And a separation pad 14 made of a material having a large friction coefficient. The separation pad 14 is urged toward the sheet feeding roller 13.

  As a transport unit for transporting the paper 12 fed from the paper feed unit on the lower side of the recording head 4, a transport belt 21 for electrostatically attracting and transporting the paper 12 and a paper feed unit A counter roller 23 for transporting the paper 12 fed through the guide 22 while sandwiching it between the transport belt 21 and the paper 12 fed substantially vertically upward is changed by approximately 90 ° and copied onto the transport belt 21. The above-described guide 22 is provided, a conveyance guide 24 serving as conveyance guide means, and a tip pressure roller 25 held by the conveyance guide 24 and biased toward the conveyance belt 21 side. In addition, a charging roller 26 as a charging unit for charging the surface of the transport belt 21 is provided.

  Here, the transport belt 21 is an endless or connected belt (these are referred to as “endless shape”), and is stretched between a transport roller 27 as a driving roller and a tension roller 28 to which tension is applied. The conveying roller 27 is driven to rotate by the sub-scanning motor 31 (FIG. 2) so as to circulate in the arrow A direction (belt conveying direction).

  As shown in FIG. 3, the transport belt 21 includes a surface layer 21a that forms a sheet adsorbing surface formed of a pure resin material having a thickness of about 40 μm that is not subjected to resistance control, for example, ETFE pure material, and the surface layer 21a. It has a back layer (medium resistance layer, earth layer) 21b made of the same material and subjected to resistance control by carbon.

  The thickness of the insulating layer (surface layer) 21a of the conveyor belt 21 affects the dielectric constant. When the thickness increases, the dielectric constant decreases and the amount of charge on the belt decreases when charged. According to the experiment, a desired electrostatic attraction force was obtained by setting the thickness of the surface layer 21a to 60 μm or less. However, in consideration of the range of film thickness that varies in manufacturing, scratches generated on the belt in the actual machine However, the electrostatic attraction force can be further improved by making the layer thickness as thin as possible within the range where the layer thickness does not become zero.

  Further, the thickness of the back layer (medium resistance layer, earth layer) 21b of the conveyor belt 21 does not directly affect the electrostatic action. However, as the total thickness of the belt increases, the rigidity increases and the belt is stretched on the actual machine. Sometimes it is difficult to ensure the flatness of the belt, while it cannot be made too thin to ensure the required strength. According to experiments, the thickness of the back layer 21b is preferably about 40 to 200 μm.

  In this way, by providing the resistance control layer 21b on the entire back side of the transport belt 21 as a two-layer structure, after the charge is formed on the surface layer 21a that is an insulating layer in advance, the charge is further increased when the sheet adsorbed to the belt comes into contact The electrostatic attraction force between the paper and the conveyor belt 21 can be increased. For example, in the case of a single insulating layer, the adsorption force is halved compared to the case of two layers, and in the case of a single layer, the position where the paper starts to contact the belt faces the ground roller located inside the belt. However, by using two layers, such a restriction is eliminated.

  In this case, a surface resistance of 1E + 10Ω / □ or more was used as the surface layer 21a, and a surface resistance of 1E + 08Ω / □ or less was used as the back layer 21b, whereby a desired electrostatic adsorption force was obtained.

  The charging roller 26 is disposed so as to contact the surface layer 21a 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.

  Further, the transport roller 27 also serves as an earth roller, is disposed in contact with the middle resistance layer 21 b of the transport belt 21, and is grounded through a ground line 29. A slit plate 32 is fixed to the shaft 27 a of the conveying roller 27, and an encoder 34 is constituted by a photo sensor 33 that detects the slit of the slit plate 32, and the sub-scanning motor 31 is driven to rotate based on the output of the encoder 34. By being controlled, the rotation amount of the conveyance roller 27, that is, the movement amount of the conveyance belt 21 is controlled.

  Here, the larger the outer diameter of the transport roller 27 provided with the slit plate 32 of the encoder 34 on the shaft 27a with respect to the count number of one rotation of the slit plate 32 constituting the encoder 34, the paper 12 for one pulse of the encoder output. The feed amount can be reduced. That is, when high-precision feeding is required, it is more advantageous to reduce the actual paper feed amount per pulse of the encoder 34, which is the control information. On the other hand, the greater the outer diameter of the roller, the greater the inertia when operating the roller, making it difficult for the printer to repeatedly start and stop the operation with high accuracy.

  Therefore, here, in order to realize high-precision control and to realize high-precision repeat stop position accuracy, the conveyance roller 27 on the upstream side in the conveyance direction is used as a drive roller, and the conveyance roller 27 which is this drive roller. Is made larger than the diameter of the tension roller 28 which is a driven roller. Specifically, the diameter of the tension roller 28 is set to the minimum diameter (actually φ16 mm) that can withstand the bending of the belt 21. Thereby, the inertial load at the time of making the conveyance belt 21 circulate becomes small, and the stop position accuracy of the conveyance belt 21 improves.

  In addition, the diameter of the conveying roller 27 as the driving roller is made larger than the diameter of the tension roller 27 as the driven roller in this way, and the conveying belt 21 on the surface of the conveying roller 27 with the conveying roller 27 as the driving roller as a reference Is set higher (larger) than the friction coefficient of the surface of the tension roller 27 as a driven roller. As a result, it is possible to prevent the image quality from being deteriorated due to slippage between the transport roller 27 and the transport belt 21.

  Further, the conveyance belt 21 does not shift (is not displaced) with respect to the conveyance roller 27 that is the driving roller, and the tension roller 28 that is the driven roller slides inside the conveyance belt 21, so that the conveyance roller 27 and the driven roller Even if the degree of axial parallelism with a certain tension roller 28 is not perfect, it is difficult for the transport belt 21 to be shifted, and the position of the paper 12 during the paper transport is prevented from changing and the image quality is prevented from deteriorating.

  Further, as shown in FIG. 4, a belt guide member 35 is disposed on the back side of the conveyance belt 21 so as to correspond to the printing region (nozzle row range) P by the recording head 4. As shown in FIG. 5, the belt guide member 35 is held between frame members 36 and 36 that hold the conveying roller 27, the tension roller 28, and the like.

  As shown in FIG. 4, the upper surface 35 a of the belt guide member 35 protrudes closer to the recording head 4 than the tangent line 37 of the two rollers (the conveyance roller 27 and the tension roller 28) that support the conveyance belt 21. . Thereby, the conveyance belt 21 is pushed up and guided by the upper surface (guide surface) 35a of the belt guide member 35 in the printing region.

  In other words, when the paper is transported in a state of being electrostatically attracted to the transport belt, the flatness of the transport belt is directly connected to the flatness of the paper. If the portion of the string stretched by the roller is used as the printing surface (image forming area by the image forming means) during belt conveyance, wrinkles of the belt are likely to occur. Further, when driving the belt, the belt may dance at the string portion of the belt that requires flatness. Therefore, the belt chord portion in the printing area where flatness is required is pushed up by the guide member from the inside of the belt so that higher belt flatness can be obtained.

  Further, as shown in FIG. 5, a plurality of grooves 35b are formed in the main scanning direction, that is, the direction orthogonal to the conveying direction, on the surface side of the belt guide member 35 that contacts the back surface of the conveying belt 21. The ribs 38 are formed to reduce the contact area with the conveyor belt 21 so that the conveyor belt 21 can move smoothly along the surface of the belt guide member 35. According to an experiment, it was confirmed that the conveyance belt 21 can smoothly move on the surface of the belt guide member 35 by setting the width of the rib 38 in the conveyance direction to 5 mm or less.

  That is, a desired charge is formed on the surface of the transport belt 21 at the printing position. The layers on the inner side of the conveyor belt 21 are influenced by the electric charge. Under such conditions, the belt 21 is supported so as to be pushed up by the belt guide member 35 from the inside of the conveyor belt 21 stretched by at least two rollers, and the surface of the belt guide member 35 is configured as a flat surface. When the transport belt 21 is supported by ribs oriented in parallel to the belt transport direction, the charge on the transport belt 21 is lost due to the movement of the transport belt 21, and the transport belt 21 and the paper 12 between the transport belt 21 and the paper 12 reach the printing area. The electrostatic attraction force acting between them may be reduced. In view of this, the ribs 38 extending in the direction (main scanning direction) orthogonal to the conveying direction of the belt guide member 35 are configured to support the inside of the belt 21, thereby preventing charge loss and increasing the adsorption force with the paper. Can be maintained.

  Further, the upstream and downstream sides of the belt guide member 35 in the transport direction are inclined portions 35c and 35d so that the transport belt 21 smoothly follows the surface of the belt guide member 35.

  Here, on the upstream side in the conveyance direction of the recording head 4, a guide portion 24 a that guides the paper on the conveyance belt 21 to a position where the conveyance belt 21 guided by the belt guide member 35 is substantially parallel to the recording head 4. A conveyance guide 24 which is a conveyance guide means is provided, and the conveyance guide 24 has a tip pressure roller 25 which is pressed and held on the conveyance belt 21 side so as to face the conveyance roller 27.

  That is, as described above, the belt guide member 35 guides the inside of the conveyor belt 21 stretched between the rollers 27 and 28, and the belt guide member 35 is configured to improve the flatness of the conveyor belt 21 with the rollers 27, If the paper 12 is disposed so as to protrude from the tangent line 28, the paper 12 adsorbed and transported to the transport belt 21 is transported while being stuck to the belt 21 from the transport roller 27 on the upstream side in the transport direction. 21 has a bent portion at a portion parallel to the recording head 4 by the belt guide member 35, the paper 21 may be separated from the transport belt 21, and the paper 21 may be separated from the transport belt 21. At this time, the leading edge of the paper 12 may come into contact with the recording head 4.

  Therefore, until the conveying belt 21 reaches a surface substantially parallel to the nozzle surface of the recording head 4 beyond the bent portion (bending point) of the conveying belt 21 (the guide surface 35a of the belt guide member 35 is parallel to the recording head 4). Until the sheet 12 is provided with a conveyance guide 24 for guiding the sheet 12, and the guide portion 24a of the conveyance guide 24 suppresses the floating of the sheet 12 to be conveyed. The sheet 12 is guided to the printing area while preventing contact with the printing area.

  Here, as shown in FIG. 6 and FIG. 7, the shaft 52 of the pressure roller 25 is supported by a groove-like support portion 51 formed on the conveyance guide 24 so as to be movable at least 0.1 mm and rotatable. The shaft 52 of the pressure roller 25 is pressed against the conveying roller 27 side by a spring 53 provided between the fixing member of the apparatus main body (not shown), and the pressure roller 25 is pressed and held on the conveying belt 21 side. The conveyance guide 24 is fixed to a fixing member of the apparatus main body (not shown).

  With this configuration, even the highly rigid paper 12 can be stably conveyed. That is, when the paper 12 to be transported has high rigidity, the transport guide 24 is lifted by its waist, and the guide portion 24a trying to press the paper 12 with the flat surface of the transport belt 21 is also lifted, so that the paper 12 cannot be pressed. May be complete.

  Further, in order to press the paper 12 closer to the vicinity of the nozzles of the recording head 4 by the guide portion 24a of the transport guide 24, the clearance between the guide portion 24a and the carriage 3 is reduced.

  Under such conditions, if the guide portion 24a of the transport guide 24 is lifted by the stiffness of the paper, it may interfere with the carriage 3. If the clearance is secured to prevent this interference, the range in which the sheet can be pressed becomes narrow, and it may be insufficient to suppress the sheet floating.

  Further, the pressure roller 25 disposed at a position facing the conveyance roller 27 sandwiches the sheet 12 by the pressure of the pressure roller 25 between the pressure roller 25 and the conveyance belt 21, and the conveyance force with respect to the sheet 12 is increased. Has the function to obtain. When the pressure roller 25 is supported by the conveyance guide 24 so as to freely rotate, a gap is generated between the pressure roller 25 and the conveyance belt 21 when the conveyance guide 24 is lifted by the stiffness of the paper 12, so It becomes impossible to obtain the conveyance force.

  Therefore, here, the conveyance guide 24 is fixed with respect to the apparatus main body, so that the guide portion 24a is prevented from floating even when a strong paper is conveyed. Since the pressure roller 25 is freely held in the roller pressing direction by the conveyance guide 24, the pressure is obtained by the spring 53 (elastic member) between the main body structure. Even if the conveyance guide 24 is fixed, the pressure roller 25 can be moved up and down in accordance with the paper thickness, and a desired pressure can be obtained and a desired conveyance force can be obtained.

  Further, as a paper discharge unit for discharging the paper 12 recorded by the recording head 4, a separation unit 41 for separating the paper 12 from the conveyance belt 22 and a paper discharge tray for stocking the paper 12 to be discharged. 42.

  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 22, and includes the transport belt 21 and the counter roller 23. The leading end is guided by the conveying guide 24 and pressed against the conveying belt 21 by the leading end pressing roller 25 to change the conveying direction by approximately 90 °.

  At this time, a positive voltage and a negative output are alternately repeated from the high-voltage power supply 30 (FIG. 1) to the charging roller 26 by a control circuit (not shown), that is, an alternating voltage is applied and the conveying belt 21 is alternately charged. In the voltage pattern, that is, in the sub-scanning direction which is the rotation 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 charge is polarized in the opposite direction to the charge pattern in the paper 12, so that a capacitor connected in parallel is formed. 12 is adsorbed by the conveyance belt 21, and the paper 12 is conveyed in the sub-scanning direction by the circular movement of the conveyance belt 21.

  Therefore, by driving the recording head 4 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 42.

Next, a second embodiment of the present invention will be described with reference to FIG. 1 is a main part configuration diagram for explaining the configuration of the apparatus, and the same reference numerals are given to portions corresponding to those in FIG.
Here, the conveyance guide 24 has a tip pressing roller 61 and a second roller 62 at the tip of the guide portion 24 (the most downstream portion in the conveyance direction).

  As shown in FIG. 9, the tip pressurizing roller 61 is obtained by applying an elastomer 64 to the surface of a base 63 made of a highly slidable resin, and the base 63 is rotatably mounted on a support shaft 65. By using a highly slidable resin for the base 63, it can be easily rotated with respect to the support shaft 65.

  As a result, even if the support shaft 65 pressurized by an elastic member such as a spring does not rotate, the roller 61 can rotate, so that the followability of the roller 61 to the transport belt 21 and the paper 12 is not hindered. The paper 12 can be pressed. Further, at this time, the occurrence of scratches on the conveyor belt 21 can be prevented.

  That is, since at least the surface layer 21a of the conveyor belt 21 is made of resin as described above, if the roller is pressed from the surface side, scratches may be made on the belt surface. When the scratch develops, the insulating layer (surface layer) 21a managed with a film thickness of 40 μm is destroyed, and if a high voltage is applied in this state, the destruction of the insulating layer 21a may develop into a leak. There is.

  Therefore, here, the surface of the roller 61 is formed of an elastomer as an elastic material to suppress the occurrence of scratches on the conveyor belt 21 and the productivity is improved by two-color molding with a highly slidable resin. Yes.

  Here, an elastomer is used as the elastic material, but rubber or other elastic resin can also be used as the elastic material. In this case, by making the elasticity of the elastic material at least softer than the elasticity of the conveyor belt, the roller can come into contact with the conveyor belt, thereby reducing the possibility that the conveyor belt is damaged.

  The guide 24a of the conveyance guide 24 is intended to guide the sheet 12 so that the sheet 12 to be conveyed is attracted to the conveyance belt 21, but the thickness of the sheet to be used varies and is the thickest. If the clearance between the guide portion 24a and the conveyance belt 21 is set in the conveyance guide 24 for the sheet, the sheet cannot be pressed by the belt 21 when the sheet is the thinnest. If the clearance is set to be narrow, the frictional resistance between the conveyance guide 24 and the paper 12 affects the overall load of the conveyance system.

  Therefore, a second roller 62 capable of pressing the paper 12 is rotatably provided at the tip of the guide portion 24a of the conveyance guide 24. The second roller 62 is conveyed by an elastic member such as a spring (not shown). The reaction force from 24 is obtained and the paper 12 is pressed against the conveyor belt 21 side.

  Thus, by providing the second roller 62 together with the roller 61 (or the roller 25), the frictional resistance between the paper 12 and the conveyance guide 24 can be reduced, and the conveyance stability of the paper is improved. Further, by adopting a configuration in which the sheet is pressed by the second roller 62, it is possible to prevent the sheet 12 from floating when the sheet 12 is efficiently pressed against the belt 21 and the transport sheet 12 reaches the printing position. In addition, the electrostatic adsorption force can be applied to the paper 12 efficiently, and the conveyance stability of the paper is improved.

  Further, when the second roller 62 is provided as described above, it is preferable to form a relief portion 66 such as a recess in the portion of the belt guide member 35 facing the second roller 62 as shown in FIG.

  That is, when the second roller 62 is tight against the belt 21 due to the dimensional variation of the parts, or when a transport sheet thicker than the gap set between the second roller 62 and the belt 21 is transported, The conveyance load of the conveyance belt 21 will increase. When the load on the conveyor belt 21 increases, it becomes difficult to make the stop position accuracy of the conveyor belt 21 itself at the time of a new line highly accurate. Further, there is a risk that the conveyor belt 21 may be damaged.

  Therefore, when the belt guide member 35 is provided as described above, the load on the conveyor belt is reduced by causing the second roller 62 to abut on the conveyor belt 21 stretched in the space above the escape portion 66. The increase can be prevented and the occurrence of scratches on the conveyor belt can be reduced.

Next, the attachment structure of the conveyance guide 24 will be described with reference to FIG.
The conveyance guide 24 is integrally provided with a pin 71 serving as a reference in the vertical direction. The pin 71 engages with a height adjusting member 72 whose height can be adjusted, and the height position is determined by the height adjusting member 72.

  Then, the apparatus main body structure (apparatus main body member) 73 is sandwiched between the conveyance guide 24 and the height adjusting member 72, and the conveyance guide 24 is fastened and fixed to the main body structure 73 with a fixing screw 74. The height adjustment member 72 is configured to be fixed to the main body structure 73 after height adjustment by a fastening member (not shown).

  Therefore, in order to fix the conveyance guide 24, the height adjusting member 72 is positioned with high accuracy with respect to the reference dimension by a jig (not shown) and fixed to the main body structure 73. Thereafter, the pins 71 of the conveyance guide 24 are guided to the height adjusting member 72 to determine the height of the conveyance guide 24. Further, the conveyance guide 24 is screwed to the main body structure 73 or the height adjusting member 72 with a fixing screw 74.

  That is, the clearance between the second roller 62 of the transport guide 24 and the transport belt 21 is determined by the assembly position of the transport guide 24. Therefore, in order to manage this clearance with high accuracy, the transport guide 23 serves as a reference transport. It is necessary to position the roller 27 with an adjustable mechanism.

  Therefore, by fixing the height position of the conveyance guide 24 to the main body structure as described above, the clearance between the second roller 62 and the conveyance belt 21 is made highly accurate, and the load on the sheet conveyance is increased. The leading edge of the paper can be reliably attached to the belt 21 and conveyed without causing it.

  In the above embodiment, the present invention has been described with reference to an example in which the present invention is applied to a serial (shuttle type) ink jet recording apparatus that is scanned by a carriage. However, the present invention is similarly applied to a line type ink jet recording apparatus having a line type head. be able to.

  The image forming apparatus according to the present invention can be applied to a facsimile apparatus, a copying apparatus, a printer / fax / copier multifunction machine, etc., in addition to an ink jet printer. Furthermore, the present invention can also be applied to an image forming apparatus that discharges a liquid other than ink, such as a resist or a DNA sample in the medical field.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is an explanatory plan view of a main part of the image forming apparatus. FIG. 2 is a schematic explanatory diagram of a conveyance belt of the image forming apparatus. FIG. 2 is an enlarged explanatory view of a main part of FIG. 1. It is a perspective explanatory view of a guide member. It is principal part plane explanatory drawing of a conveyance guide. It is side surface explanatory drawing of FIG. It is a principal part schematic block diagram of the image forming apparatus which concerns on 2nd Embodiment of this invention. FIG. 4 is a cross-sectional explanatory view of a tip pressing roller of the image forming apparatus. It is the principal part expansion explanatory drawing of a guide member similarly. It is explanatory drawing of the position adjustment attachment structure of a conveyance guide.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Carriage 4 ... Recording head 12 ... Paper 21 ... Conveyance belt 24 ... Conveyance guide 25 ... Tip pressure roller 26 ... Charging roller 27 ... Conveyance roller 28 ... Tension roller 35 ... Belt guide member.

Claims (13)

In an image forming apparatus that adsorbs and conveys a sheet on the surface of a conveying belt and forms an image on the sheet by an image forming unit
Span the conveyor belt between at least two rollers;
Belt guide means for guiding the conveying belt from the inside at a position facing the image forming means is provided so that a guide surface protrudes from a tangent line of the two rollers;
The image forming apparatus includes a conveyance guide unit that guides the sheet sucked and conveyed by the conveyance belt from a position in front of the image forming unit and the conveyance belt that are substantially parallel to a position that is substantially parallel. apparatus.   The image forming apparatus according to claim 1, wherein the conveyance guide unit includes a roller that is pressed and held on the conveyance belt side so as to face the roller on the upstream side in the conveyance direction and presses the sheet. Image forming apparatus.   3. The image forming apparatus according to claim 2, wherein the roller provided on the conveyance guide unit is movable in the pressurizing direction and is rotatably held by the conveyance guide unit, and pressurizes a shaft that supports the roller. An image forming apparatus comprising: a pressure unit; and the conveyance guide unit is fixed to a main body.   4. The image forming apparatus according to claim 2, wherein at least a surface of the roller provided in the conveyance guide unit is formed of an elastic material, and the elastic material is formed of an elastomer, rubber, or an elastic resin, and at least the elasticity thereof is An image forming apparatus characterized in that it is softer than the elasticity of the conveying belt in contact therewith.   5. The image forming apparatus according to claim 1, wherein the conveyance guide unit does not contact the belt guide unit via the conveyance belt.   6. The image forming apparatus according to claim 5, wherein a second roller is rotatably provided at a most downstream portion in the transport direction of the transport guide unit, and the belt guide unit corresponds to the second roller. An image forming apparatus, wherein an escape portion that does not contact the inside of the conveyor belt is formed at a position.   7. The image forming apparatus according to claim 6, wherein at least two ribs are formed on the guide surface of the belt guide unit in a direction orthogonal to the sheet conveying direction, and a space between the ribs is used as the escape portion. An image forming apparatus.   8. The image forming apparatus according to claim 7, wherein at least one rib of the belt guide means has a width of 5 mm or less.   9. The image forming apparatus according to claim 6, wherein the second roller is capable of pressing a sheet to be conveyed against the conveying belt.   10. The image forming apparatus according to claim 1, wherein a roller on the upstream side in the sheet conveying direction is a driving roller.   The image forming apparatus according to claim 10, wherein the driving roller has a diameter larger than that of the other rollers.   12. The image forming apparatus according to claim 10, wherein the driving roller has a larger coefficient of friction with the inner surface of the conveying belt than other rollers.   13. The image forming apparatus according to claim 1, wherein the conveyance guide unit is fixed to an apparatus main body member so that a height position of the conveyance guide unit can be adjusted with respect to the conveyance belt. .

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