JP2014177317A - Sheet conveyance device and image formation apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet conveyance device capable of stably separating and conveying a top sheet from a sheet bundle, and an image formation apparatus using the same.SOLUTION: A sheet conveyance device 10 includes an endless moving attraction belt 2 which is tensed between an upstream-side tension roller 5 and a downstream-side tension roller 6, and arranged opposite an upper surface of a sheet bundle 1 having sheets stacked; an air jet part 9 which jets air from a downstream-side end in a sheet conveying direction toward the sheet bundle 1 so as to float and separate sheets; and an electrode member 3 which attracts a floated and separated top most sheet 1a to the attraction belt 2 with electrostatic force, and conveys the top sheet 1a by the endless movement of the attraction belt 2 after attracting the floated and separated top most sheet 1a to the attraction belt 2. A tension surface 2a of the attraction belt 1 which faces an upper surface of the sheet bundle is inclined so that when the air is jetted by the air jet part 9, an upstream side of the sheet conveying direction is above the downstream side of the sheet conveying direction.

Description

  The present invention relates to a sheet conveying apparatus that separates and conveys the uppermost sheet from a stacked sheet bundle, and an image forming apparatus using the same.

  Conventionally, as a method for separating and transporting the uppermost sheet from a bundle of sheets such as stacked originals and recording materials, a friction feeding method using friction force, an air separation feeding method using air suction, and electrostatic adsorption are used. A known electrostatic feeding method is known.

  In the friction feeding method, a pickup member such as a roller or a belt made of a material such as rubber that can obtain a high coefficient of friction with respect to the sheet is brought into contact with the uppermost sheet of the sheet bundle, and the uppermost sheet is removed from the sheet bundle. Pick up. The friction feeding method has a simple configuration, but in order to obtain a large frictional force between the pickup member and the sheet, it is necessary to strongly press the pickup member against the sheet surface by a biasing means such as a spring. And Such a biasing means such as a spring usually decreases with time due to deterioration over time, so it is difficult to obtain stable feeding performance over time. Further, the pickup member made of rubber or the like deteriorates with time or according to the environment, and the coefficient of friction with respect to the sheet decreases, so that it is difficult to obtain stable feeding performance in this respect as well.

  Also, due to diversification of users, sheets having various functions and applications such as coated paper and label paper are often used as recording materials for recording images, as well as plain paper. The types of sheets used as recording materials are expected to increase in the future. A sheet having a special function or application has an extremely small coefficient of friction with respect to the pickup member, and such a sheet is difficult to be stably picked up by a friction feeding method. In addition, a sheet whose surface part is easily peeled off from the sheet body, such as an adhesive label, is stabilized by the friction feeding method because the sheet surface part is peeled off from the sheet body due to the frictional force between the pickup member and the sheet. It is difficult to pick up.

  In the air separating and feeding method, air is ejected to a sheet bundle to separate the sheets from each other, and the uppermost sheet that has floated is adsorbed to a suction belt by a suction force and conveyed (for example, Patent Document 1). The air separation and feeding method is a non-friction separation method that does not depend on the friction coefficient of the pickup member or the sheet. However, because negative pressure is generated and the sheet is sucked by the suction belt, the surface of the sheet may be damaged by excessive negative pressure, or the suction holes formed in the suction belt may be transferred to the surface of the sheet. There is a case.

  In view of this, attention has been focused on the use of an electrostatic feeding method in which air is blown to a sheet bundle to float the sheet, and the uppermost sheet is electrostatically adsorbed on the surface of an adsorption belt made of a dielectric. In the electrostatic feeding method using air, an alternating charge is applied to a suction belt wound around a plurality of rollers, and the charged uppermost sheet is sucked by the charged suction belt. When the uppermost sheet is adsorbed by the belt, the adsorption belt is driven to rotate, and the uppermost sheet adsorbed by the adsorption belt is conveyed toward the conveying roller pair. As described above, the electrostatic feeding method is also a non-friction separation method that does not depend on the friction coefficient of the pickup member or the sheet.

  However, in the electrostatic feeding method using air, the air is ejected toward the downstream end portion of the sheet bundle in the sheet conveying direction to float the sheet. For this reason, the uppermost sheet may be adsorbed to the upstream end portion in the sheet conveying direction before the downstream end portion in the sheet conveying direction of the suction belt. As a result, the passage of air sprayed from the downstream side in the sheet conveying direction is blocked by the adsorbed portion, and air stays between the adsorption belt and the uppermost sheet, and the uppermost sheet is stabilized on the adsorption belt. It becomes difficult to adsorb in a state.

  SUMMARY An advantage of some aspects of the invention is that it provides a sheet conveying apparatus capable of stably separating and conveying the uppermost sheet from a sheet bundle, and an image forming apparatus using the sheet conveying apparatus.

  In order to solve the above-mentioned problems, the invention of claim 1 is directed to a suction belt that is stretched by a plurality of stretching rollers and is disposed opposite to an upper surface of a sheet bundle on which sheets are stacked, and moves endlessly. Air jetting means for jetting air from the downstream side in the sheet conveying direction and air separating means for separating the sheet and suction means for adsorbing the floated and separated uppermost sheet to the suction belt by electrostatic force. In the sheet conveying apparatus that conveys the uppermost sheet by endless movement of the adsorption belt after being adsorbed by the adsorption belt, a stretched surface facing the upper surface of the sheet bundle of the adsorption belt is formed when air is ejected by the air ejection means. Further, the sheet conveying direction upstream side is inclined so as to be higher than the sheet conveying direction downstream side.

  In the present invention, the uppermost sheet floated and separated by air ejection from the air ejection means comes into contact with the downstream end of the suction belt in the sheet transport direction and is adsorbed by the suction belt before the upstream end of the suction belt in the sheet transport direction. Will be. Therefore, no air stays between the suction belt and the uppermost sheet when air is ejected, and the uppermost sheet can be stably adsorbed to the suction belt, and the uppermost sheet can be stably removed from the sheet bundle. Can be separated and transported.

1 is a schematic diagram showing a configuration of a copier according to an embodiment. FIG. 2 is a schematic diagram illustrating a configuration of a paper feeding unit of the copier. In the sheet conveying apparatus according to the first embodiment, a schematic diagram illustrating a state at the time of starting a sheet conveying operation, (b) is a schematic diagram illustrating a state at the time of air ejection, and (c) is a state at the time of sheet adsorption. FIG. The principal part expansion schematic diagram which shows the structure of the sheet conveying apparatus which concerns on 2nd embodiment. In the sheet conveying apparatus according to the third embodiment, (a) is a configuration diagram illustrating a configuration when the moving mechanism pushes down the upstream tension roller, and (b) is a cross-sectional view taken along line AA in (a). . In the sheet conveying apparatus, (a) is a configuration diagram illustrating a configuration when the moving mechanism pushes up the upstream tension roller, and (b) is a cross-sectional view taken along line AA of (a). FIG. 6 is a schematic diagram for explaining a state when the lower tension surface of the suction belt is inclined when air is ejected in the sheet conveying apparatus. The schematic diagram explaining a mode when the lower stretched surface of an adsorption belt is horizontal at the time of air ejection in the sheet conveying apparatus. FIG. 6 is a schematic diagram for explaining a state when the lower tension surface of the suction belt is inclined during sheet conveyance in the sheet conveying apparatus. FIG. 6 is a schematic diagram for explaining a state when the lower stretched surface of the suction belt is horizontal during sheet conveyance in the sheet conveying apparatus. FIG. 10 is a schematic diagram illustrating a state when air is ejected from a conventional sheet conveying apparatus.

  Hereinafter, an embodiment in which the present invention is applied to a copying machine which is an electrophotographic image forming apparatus will be described. Needless to say, the present invention can be applied not only to the image forming apparatus according to the present embodiment but also to an inkjet image forming apparatus, for example.

  FIG. 1 is a schematic diagram showing a configuration of a copying machine according to the present embodiment. FIG. 2 is a schematic diagram showing the configuration of the paper feeding unit of the copying machine. As shown in FIG. 1, the copier 50 mainly includes an image forming unit 51, a paper feeding unit 52, a document reading unit 58, an automatic document conveying unit 59, and the like. The sheet feeding unit 52 accommodates a sheet bundle 1 in which a plurality of recording material sheets (hereinafter referred to as sheets) are stacked, and an uppermost sheet 1a located at the highest position from the sheet bundle 1 is an image forming unit. Paper is fed to 51. The image forming unit 51 forms an image on the sheet fed from the paper feeding unit 52 based on image data such as a document image read by the document reading unit 58. The automatic document feeder 59 separates documents one by one from the bundle of documents placed on the document tray 59a and automatically feeds them to the contact glass on the document reading unit 58. The document reading unit 58 reads the document transported on the contact glass by the automatic document transport unit 59. The document reading unit 58 is attached to be freely opened and closed via an opening / closing mechanism (for example, a hinge) (not shown), and the document can be read by placing the document on the contact glass.

  The image forming unit 51 includes a charging device 62, a developing device 64, a transfer device 64, a photoconductor cleaning device 65, and the like around a photoconductor 61 as a latent image carrier. The image forming unit 51 also includes an optical writing unit (not shown) for irradiating the photoreceptor 61 with the laser beam 63, a fixing device 55 for fixing the toner image on the sheet, and the like.

  In the image forming unit 51 configured as described above, as the photosensitive member 61 rotates, the surface of the photosensitive member 61 is first uniformly charged by the charging device 62. Next, the optical writing unit irradiates the photosensitive member 61 with the laser beam 63 based on the image data of the original image read by the original reading unit 58 or the image data input from a personal computer or the like. An electrostatic latent image is formed. Thereafter, a toner image is formed on the photosensitive member 61 by attaching toner with the developing device 64 to visualize the electrostatic latent image. On the other hand, the sheet feeding unit 52 separates and conveys the sheets one by one, and abuts against the registration roller 53 to stop. Then, in synchronization with the toner image formation timing of the image forming unit 51, the sheet that has been pressed against the registration roller 53 and stopped is sent to the transfer unit where the photoconductor 61 and the transfer device 54 face each other. In the transfer unit, the toner image on the photoconductor 61 is transferred to the supplied sheet. The sheet onto which the toner image has been transferred is fixed to the toner image by the fixing device 55 and then discharged to the paper discharge tray 57 by the paper discharge roller pair 56. On the other hand, the toner remaining on the surface of the photoreceptor 61 after the toner image transfer is removed by the photoreceptor cleaning device 65 to prepare for image formation again.

  As shown in FIG. 2, the sheet feeding unit 52 is positioned at the top of the sheet feeding cassette 11 that stacks and stores the sheet bundle 1 composed of a plurality of sheets, and the sheet bundle 1 on the sheet feeding cassette 11. It is mainly comprised from the sheet conveying apparatus 10 which isolate | separates and conveys the uppermost sheet | seat 1a.

  A bottom plate 7 on which the stacked sheet bundle 1 is stacked is installed in the sheet feeding cassette 11 of the sheet feeding unit 52. A support member 8 that supports the bottom plate 7 is rotatably mounted between the bottom plate 7 and the bottom portion of the paper feed cassette 11, and the bottom plate 7 can be moved up and down by rotating the support member 8.

  Further, the sheet feeding unit 52 is provided with a filler sensor 12 that detects that the uppermost sheet 1a of the sheet bundle 1 has reached a predetermined position. The filler sensor 12 is a transmission type optical sensor (not shown) having a filler 12b rotatably supported by a shaft 12a provided in the apparatus main body, and a light emitting portion and a light receiving portion arranged to face each other across the rotation path of the filler 12b. It consists of and.

  The sheet conveying apparatus 10 is an air ejection unit 9 that is an air ejection unit that ejects air toward the sheet bundle 1 from the downstream side in the sheet conveyance direction in order to separate the uppermost sheet 1a from the sheet bundle 1 on the sheet feeding cassette 11. It has. The air ejection unit 9 blasts the sheets 1a, 1b,... Of the sheet bundle 1 by separating air from the downstream side of the sheet bundle 1 in the sheet conveyance direction at a predetermined timing.

  Further, the sheet conveying device 10 includes an adsorption belt 2 stretched between an upstream stretching roller 5 installed upstream in the sheet conveying direction and a downstream stretching roller 6 installed downstream in the sheet conveying direction. It has. Stopping ribs (not shown) are provided on the inner sides of both side edges of the suction belt 2 and engage with both side end surfaces of the stretching rollers 5 and 6 to prevent the belt from shifting.

The adsorption belt 2 includes a dielectric layer having a resistance of 10 ⁸ Ω · cm or more, for example, a surface layer made of polyethylene terephthalate having a thickness of about 50 μm, and a back surface having a resistance of 10 ⁶ Ω · cm or less formed by aluminum vapor deposition. It has a two-layer structure composed of layers. By making the suction belt have the two-layer structure as described above, the suction belt 2 is in a favorable charged state.

The upstream tension roller 5 is provided with a conductive rubber layer having a resistance value of 10 ⁶ Ω · cm on the surface, and the downstream tension roller 6 is a metal roller. Both the upstream tension roller 5 and the downstream tension roller 6 are grounded. The downstream tension roller 6 is intermittently driven by a drive motor (not shown) via a drive transmission member such as an electromagnetic clutch according to a paper feed signal. The upstream tension roller 5 rotates following the rotation of the suction belt 2. As a result, the suction belt 2 moves endlessly with the lower tension surface 2 a stretched between the upstream tension roller 5 and the downstream tension roller 6 facing the upper surface of the sheet bundle 1. In this embodiment, the downstream tension roller 6 is a drive roller, but any tension roller may be connected to a drive source.

  Here, the upstream tension roller 5 and the downstream tension roller 6 have substantially the same diameter, and the lowest point of the upstream tension roller 5 is higher than the lowest point of the downstream tension roller 6. It is arranged to come. As a result, the lower stretched surface 2a facing the upper surface of the sheet bundle 1 of the suction belt 2 is inclined so that the upstream side in the transport direction is upward, that is, upward in the drawing.

  Also, on the surface of the suction belt 2, there is a blade-like electrode member 3 as suction means that forms a potential pattern by contacting the surface of the suction belt 2 at a position wound around the downstream tension roller 6. Touching. The electrode member 3 is connected to a charging power source 4 that generates alternating current, and the surface of the suction belt 2 has a pitch (pitch should be about 2 mm to 16 mm) according to the AC power source frequency and the circumferential speed of the suction belt 2. An alternating potential pattern is formed. In addition to alternating current, the charging power source 4 may be one in which direct current is changed to high and low alternate potentials, such as a rectangular wave and a sine wave. In this embodiment, a sine wave having an amplitude of 4 kV is applied to the surface of the suction belt 2 by the charging power source 4.

  The electrode member 3 is in contact with the surface layer of the suction belt 2 because the back layer of the suction belt 2 grounded via the upstream tension roller 5 and the downstream tension roller 6 is used as a counter electrode. It may be placed anywhere as long as it is a position. The electrode member 3 is not limited to a blade shape, and may be configured in a roller shape. The blade-shaped electrode member has an advantage that it can be manufactured at a lower cost than the roller-shaped electrode member. In addition, the blade-like electrode member can easily reduce the alternating charging interval to a small pitch, and can perform stable charging even if the adsorption belt has a minute wave. On the other hand, the roller-shaped electrode member has an advantage that the durability is high because the frictional resistance is smaller than that of the blade-shaped electrode member. In addition, the blade-like electrode member does not come into contact with the suction belt when the electrode member itself is wavy, but the roller-like electrode member has an advantage that it can be charged reliably as the nip is formed.

  Next, a sheet conveying operation using the sheet conveying apparatus according to the present embodiment will be described with reference to FIG. FIG. 3A is a schematic diagram for explaining the state at the start of the sheet conveying operation, FIG. 3B is a schematic diagram for explaining the state at the time of air ejection, and FIG. 3C is a schematic diagram for explaining the state at the time of sheet adsorption. It is.

  First, as shown in FIG. 3A, a driving means (not shown) is driven by a paper feed signal to rotate the downstream tension roller 6 and rotate the suction belt 2. Next, an alternating voltage is applied to the rotating suction belt 2 by the charging power source 4 via the electrode member 3, and the potential alternating on the surface of the suction belt 2 with a pitch corresponding to the AC power frequency and the circumferential speed of the suction belt 2. Form a pattern.

  When charging of the suction belt 2 is completed, the rotation of the suction belt 2 is stopped. Then, the support member 8 is rotated by a support member drive motor (not shown) to start raising the bottom plate 7. The sheet bundle 1 stacked on the bottom plate 7 rises, and the uppermost sheet 1 a comes into contact with the filler 12. At this time, the light receiving unit of the transmission optical sensor receives light from the light emitting unit. Further, when the bottom plate 7 is raised, the filler 12 blocks the light from the light emitting portion, and the light receiving portion does not receive the light. Thereby, it is detected that the uppermost sheet 1a of the sheet bundle 1 has come to a predetermined position, and the rotation of the support member 8 is stopped.

  Next, as shown in FIG. 3B, when the uppermost sheet 1 a of the sheet bundle 1 comes to a predetermined position, air is sprayed toward the sheet bundle 1 from the downstream side in the sheet conveying direction by the air ejection unit 9. As a result, several sheets 1a, 1b,... At the upper position of the sheet bundle 1 are levitated, and the levitated uppermost sheet 1a contacts the lower stretched surface 2a of the suction belt 2.

  When the uppermost sheet 1a comes into contact with the adsorption belt 2, Maxwell's stress acts on the uppermost sheet 1a, which is a dielectric, due to an unequal electric field formed by the potential pattern on the surface of the adsorption belt 2, and the uppermost sheet 1a Adsorb to the adsorption belt 2. This adsorption force acts only on the uppermost sheet 1a and does not act on the second and subsequent sheets 1b. At this time, as shown in FIG. 3C, the lower stretched surface 2a of the suction belt 2 is inclined so that the upstream side in the transport direction is upward. Therefore, the uppermost sheet 1 a is adsorbed to the adsorption belt 2 at a position where the adsorption belt 2 is wound around the downstream tension roller 6 before the position where the adsorption belt 2 is wound around the upstream tension roller 5. Become.

  Here, the sheet conveying apparatus 100 in which the lower stretched surface 102a of the suction belt 102 is configured horizontally will be described with reference to FIG. As shown in FIG. 11, in the sheet conveying apparatus 100, the lower stretched surface 102 a of the suction belt 102 is horizontal when air is ejected by the air ejection unit 109. Therefore, as described above, the uppermost sheet 101a may be attracted to the suction belt at a position where the uppermost sheet 101a is wound around the upstream tension roller 105 before the position where the uppermost sheet 101a is wound around the downstream tension roller 106. is there. As a result, air stays in a portion indicated by Y in FIG. 11, and the adsorption of the uppermost sheet 1a becomes unstable.

  In contrast, in the sheet conveying apparatus 50 according to the present embodiment, as shown in FIG. 3C, the position of the upstream tension roller 5 is higher than the position of the downstream tension roller 6. Therefore, the uppermost sheet 1a is attracted to the suction belt 2 at a position where the suction belt 2 is wound around the downstream tension roller 6 before the position where the suction belt 2 is wound around the upstream tension roller 5. . That is, the uppermost sheet 1a is adsorbed by the adsorption belt 2 at the downstream end in the sheet conveyance direction before the upstream end in the sheet conveyance direction of the adsorption belt 2, and between the adsorption belt 2 and the uppermost sheet 1a. No air stagnation occurs.

  Next, when the uppermost sheet 1a is adsorbed to the lower tension surface 2a of the adsorption belt 2, the air ejection from the air ejection section 9 is stopped. Then, the suction belt 2 is rotated by a drive motor (not shown), and the uppermost sheet 1 a sucked on the suction belt 2 is conveyed toward the conveyance roller pair 13. When the leading edge of the uppermost sheet 1a adsorbed on the adsorption belt 2 reaches the winding portion of the downstream tension roller 6 of the adsorption belt 2, the uppermost sheet 1a is separated from the adsorption belt 2 by the curvature separation, and the conveying roller Move towards pair 13. The linear velocity of the suction belt 2 and the conveyance roller pair 13 is the same. When the conveyance roller pair 13 is intermittently driven at a timing, the adsorption belt 2 is also driven to be intermittently driven. Control the motor.

  When it is difficult to separate the uppermost sheet 1a from the suction belt 2 only by the curvature separation by the downstream tension roller 6 when the uppermost sheet 1a adsorbed to the suction belt 2 is conveyed, the downstream tension roller A separation claw may be installed on the surface of the suction belt 2 wound around the belt 6. Separation assistance is performed by the separation claw, so that the uppermost sheet 1a can be reliably separated from the suction belt 2.

  Further, charging of the suction belt 2 is performed for the length from the sheet separation position of the suction belt 2 to the conveying roller pair 13, and thereafter, the suction belt 2 is neutralized by the electrode member 3. Good. As a result, the uppermost sheet 1a is conveyed by only the conveying force of the conveying roller pair 13 without being influenced by the suction belt 2 after being conveyed to the conveying roller pair 13. Further, by neutralizing the suction belt 2, it is possible to suppress the second sheet 1 b from being electrostatically attracted to the separated suction belt 2.

Here, the principle that the charge of the charged suction belt 2 can be removed by applying an alternating voltage to the rotating suction belt 2 will be described. When a charging electrode such as the electrode member 3 is brought into contact with the outer peripheral surface of a charged body such as the adsorbing belt 2 that moves around and a DC voltage is applied by a DC power source, the charged body is a voltage that is equal to or lower than a certain voltage. Is not charged. This voltage of charge starting voltage V _0. The charging start voltage value V ₀ varies depending on the thickness of the member to be charged, volume resistance, and the like. Next, when an alternating voltage having the charging start voltage V ₀ as a peak value is applied to the charging electrode, it is confirmed that the surface potential of the charged object is neutralized to almost zero V. . This is because, by setting the peak value of the applied voltage to the charging start potential V ₀ , this applied voltage does not have the ability to charge the charged object that is a dielectric, but the space charge charged to the charged object It means that the moving force works and it can be neutralized. In addition, since an alternately applied voltage is used, there is a static elimination effect regardless of whether the charged body is charged to (+) or (-). However, when the applied voltage was equal to or lower than the charging start voltage V ₀ , charge removal was insufficient. When the applied voltage was equal to or higher than the charging start voltage, charging was applied at the applied frequency, and the charge could not be discharged to zero V. Therefore, the alternating voltage applied to the suction belt 2 for charge removal may be controlled so that the peak value becomes the charging start voltage V ₀ for the suction belt 2.

[Second Embodiment]
Next, a sheet conveying apparatus according to the second embodiment will be described. FIG. 4 is a main part enlarged schematic view showing the configuration of the sheet conveying apparatus according to the second embodiment. In FIG. 4, the same members as those described in FIG.

  As shown in FIG. 4, the sheet conveying apparatus 20 according to the second embodiment has a diameter of the upstream tension roller 25 smaller than the diameter of the downstream tension roller 26, and the lowermost of the upstream tension roller 25. The point is arranged so as to be above the lowest point of the downstream tension roller 26. As a result, the upper tension surface 2b of the suction belt 2 is substantially horizontal, and the lower tension surface 2a of the suction belt 2 is positioned above the upper surface of the sheet bundle 1 so that the upstream side in the conveying direction is located upward. Inclined so that it rises to the middle left.

  Compared to the first embodiment in which the upstream tension roller 25 and the downstream tension roller 26 have the same diameter, the sheet conveying device 20 having such a configuration requires a space above the suction belt 2 (see FIG. (Part indicated by X in 4) can be reduced, and space saving can be achieved. The downstream tension roller 26 is suitable for separating the uppermost sheet 1a from the adsorption belt 2 by the curvature when the adsorption belt 2 is moved endlessly and the uppermost sheet 1a adsorbed to the adsorption belt 2 is conveyed. It has a diameter.

[Third embodiment]
Next, a sheet conveying apparatus according to the third embodiment will be described. FIG. 5A is a configuration diagram illustrating a configuration when the moving mechanism pushes down the upstream tension roller, and FIG. 5B is a cross-sectional view taken along line AA in FIG. FIG. 6A is a configuration diagram illustrating a configuration when the moving mechanism pushes up the upstream tension roller, and FIG. 6B is a cross-sectional view taken along line AA in FIG. FIG. 7 is a schematic diagram for explaining a state in which the lower tension surface of the suction belt is inclined when air is ejected. FIG. 8 is a schematic diagram for explaining a state in which the lower tension surface of the suction belt is horizontal when air is ejected. FIG. 9 is a schematic diagram for explaining a state where the lower tension surface of the suction belt is inclined during sheet conveyance. FIG. 10 is a schematic diagram illustrating a state where the lower tension surface of the suction belt is horizontal during sheet conveyance. 5 to 10, the same members as those described in FIG. 2 are denoted by the same reference numerals and description thereof is omitted.

  The sheet conveying device 30 according to the third embodiment moves as a moving means for moving the position of the upstream tension roller 35, as shown in FIGS. 5 (a), 5 (b) and 6 (a), 6 (b). A mechanism 31 is provided. The moving mechanism 31 includes a cam 32 that is rotatably provided in contact with the upper portion of the rotation shaft 35a of the upstream tension roller 35, and a cam drive motor (not shown) that rotationally drives the rotation shaft 32a of the cam 32. . The moving mechanism 31 is a biasing member that contacts the lower portion of the rotary shaft 35a of the upstream tension roller 35 and biases the rotary shaft 35a in a direction away from the upper surface of the sheet bundle 1 (upward in the figure). A spring 33 is provided. Further, the moving mechanism 31 includes a box-shaped restricting member 34 that restricts the movement of the rotating shaft 35a of the upstream tension roller 35 in the vertical direction in the figure. As shown in FIG. 5, when the cam 32 is rotated so that the long diameter portion of the cam 32 is in contact with the rotation shaft 35 a of the upstream tension roller 35, the upstream tension roller 35 has the rotation shaft 35 a of the spring 33. It moves downward in the figure while being guided by the restricting member 34 against the bias. On the other hand, as shown in FIG. 6, when the cam 32 is rotated so that the small diameter portion of the cam 32 is in contact with the rotation shaft 35 a of the upstream tension roller 35, the rotation shaft 35 a is spring-loaded. It is urged upward in the figure by 33 and moves upward in the figure while being guided by the regulating member 34. In this way, by rotating the cam 32 by a cam drive motor (not shown), the upstream tension roller 35 (the rotation shaft 35a thereof) is biased by or against the bias of the spring 33. It can be moved in the vertical direction in the figure.

  The downstream tension roller 36 includes a spring 37 that contacts the rotation shaft 36a of the downstream tension roller 36 and urges the rotation shaft 36a away from the upstream tension roller 35, and a rotation shaft 36a. And a regulating member 38 that regulates movement in the horizontal direction in the figure. As a result, the downstream tension roller 36 is urged by the spring 37 in the horizontal direction away from the upstream tension roller 35. The downstream tension roller 36 thus biased applies a biasing force to the suction belt 2 in a direction away from the upstream tension roller 35 so that the suction belt 2 is stretched with a predetermined tension. I have to.

  In this way, by adopting a configuration in which the upstream tension roller 35 can be moved by the moving mechanism 31, it is possible to perform separation conveyance according to the paper type of the sheet. For example, as shown in FIG. 7, when a sheet 1 a ′ having strong stiffness (high bending rigidity) such as thick paper is conveyed, if the lower tension surface 2 a of the suction belt 2 is inclined, the sheet The sheet 1a ′ may be peeled off from the suction belt 2 because the bending rigidity of 1a ′ exceeds the suction force. Therefore, when conveying a strong sheet 1a ′, as shown in FIG. 8, the upstream tension roller 35 is pushed down by the above-described moving mechanism 31 so that the lower tension surface 2a of the suction belt 2 is horizontal. It is good to be. When the strong sheet 1a ′ is used, the sheet 1a ′ does not flutter when the air is ejected. Therefore, the sheet 1a ′ is not attracted from the upstream end of the suction belt 2 in the sheet conveyance direction, and the lower tension of the suction belt 2 is Even if the mounting surface 2a is horizontal, no air stays.

  On the other hand, when transporting a sheet of paper type with small stiffness (low bending rigidity) such as thin paper, the uppermost sheet 1a is likely to flutter when air is blown, and as described above, the lower stretch of the suction belt 2 is stretched. Air retention is likely to occur when the surface 2a is horizontal. Therefore, when a sheet having a small stiffness is used, it is preferable that the upstream tension roller 35 is pushed up by the above-described moving mechanism 31 so that the lower tension surface 2a of the suction belt 2 is inclined. In this way, by separating the upstream tension roller 35 during the air ejection according to the paper type of the sheet, the sheet can be stably separated.

  However, when the position of the upstream tension roller 35 is made variable for each sheet type, the conveyance angle at which the uppermost sheet 1a separated from the suction belt 2 enters the conveyance roller pair 13 changes. Therefore, as shown in FIG. 9, the leading edge of the uppermost sheet 1 a separated from the suction belt 2 may not enter the nip of the conveying roller pair 13, and a jam may occur before the conveying roller pair 13. Therefore, after the sheet is adsorbed on the suction belt 2, the upstream tension roller 35 is moved to a predetermined position so that the nip of the conveying roller pair 13 is on the plane with the lower tension surface 2a of the suction belt 2. Good. For example, as illustrated in FIG. 10, after the sheet is adsorbed to the suction belt 2, the upstream tension roller 35 is lowered by the moving mechanism 31, and the conveyance roller pair is placed on a plane having the lower tension surface 2 a of the suction belt 2. It is preferable to have 13 nips. As a result, it is possible to prevent a jam from occurring before the transport roller pair 13.

  In the sheet conveying apparatus 30 according to the third embodiment, the configuration in which the diameters of the stretching rollers 35 and 36 are substantially the same has been described. However, as described in the second embodiment, the upstream stretching roller You may comprise so that the diameter of 35 may become smaller than the diameter of the downstream tension roller 36. FIG. In the first, second, and third embodiments, a configuration in which the suction belt 2 is stretched by the upstream stretching rollers 5, 25, 35 and the downstream stretching rollers 6, 26, 36 is employed. However, a configuration may be adopted in which a tension roller is further added and stretched by three or more tension rollers.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
A suction belt 2 that is stretched by a plurality of stretching rollers such as an upstream stretching roller 5 and a downstream stretching roller 6 and that is disposed opposite to an upper surface of a sheet bundle such as a sheet bundle 1 on which sheets are stacked and moves endlessly. An air ejection means such as an air ejection unit 9 for ejecting air from the downstream end in the sheet conveying direction toward the sheet bundle, and an uppermost sheet 1a such as the uppermost sheet 1a Adsorbing means such as an electrode member 3 that adsorbs the sheet to the adsorbing belt by electrostatic force, and the uppermost sheet separated by floating is adsorbed to the adsorbing belt, and then the uppermost sheet is conveyed by endless movement of the adsorbing belt In the sheet conveying apparatus such as the sheet conveying apparatus 10, 20, 30 or the like, the stretched surface facing the upper surface of the sheet bundle of the suction belt is at the time of air ejection by the air ejection means, Over preparative upstream side is inclined so that the upper than in the downstream side in the sheet conveyance direction.
According to this, as described in the first, second, and third embodiments, the uppermost sheet that is floated and separated by the air ejection from the air ejection means is from the upstream end of the suction belt in the sheet conveyance direction. First, it comes into contact with the downstream end portion in the sheet conveying direction and is sucked by the suction belt. Therefore, no air stays between the suction belt and the uppermost sheet when air is ejected, and the uppermost sheet can be stably sucked onto the suction belt. In the sheet conveying device according to the first embodiment, the positions of the upstream tension roller and the downstream tension roller are fixed, and the inclination angle of the lower tension surface of the suction belt is constant. Therefore, it is only necessary to install a drive system for rotationally driving the suction belt, and it is not necessary to install moving means for moving the stretching roller in order to adjust the distance between the suction belt and the upper surface of the sheet bundle. Therefore, the sheet conveying apparatus according to the first embodiment has a simple configuration, and there is an advantage that space saving and cost reduction can be achieved.
(Aspect B)
In the sheet conveying apparatus of (Aspect A), the diameter of the stretching roller on the most upstream side in the sheet conveying direction among the plurality of stretching rollers is smaller than the diameter of the stretching roller on the most downstream side in the sheet conveying direction.
According to this, as described in the second embodiment, the space required above the suction belt can be reduced, and the space can be saved.
(Aspect C)
In the sheet conveying apparatus according to (Aspect A) or (Aspect B), a tension roller moving unit such as a moving mechanism 31 that moves the position of the tension roller is provided, and the tension roller moving unit corresponds to the type of sheet. Thus, the tension roller is moved when air is blown by the air blowing means.
According to this, as explained in the third embodiment, the suction belt can suck the uppermost sheet in a stable state regardless of the type of the sheet.
(Aspect D)
In the sheet conveying apparatus according to (Aspect C), the sheet conveying apparatus includes a conveying roller pair such as a conveying roller pair 13 that conveys the sheet separated from the adsorption belt, and the stretching roller moving unit has the uppermost sheet adsorbed to the adsorption belt Thereafter, the tension roller is moved so that the nip of the pair of conveying rollers is on a plane with a tension surface facing the upper surface of the sheet bundle of the suction belt.
According to this, as described in the third embodiment, it is possible to prevent a jam or the like from being generated in the pair of conveying rollers even if the stretching roller is moved according to the type of the sheet. .
(Aspect E)
An image forming apparatus comprising: an image forming unit such as an image forming unit 51 that forms an image on a sheet; and a sheet conveying unit that separates the uppermost sheet from the stacked sheet bundle and conveys the sheet to the image forming unit. The sheet conveying device according to claim 1, 2, 3 or 4 is used as the sheet conveying means.
According to this, as described in the first, second, and third embodiments, the sheet can be separated and conveyed and stable image formation is possible.

DESCRIPTION OF SYMBOLS 1 Sheet bundle 2 Adsorption belt 3 Electrode member 4 Charging power supply 5, 25, 35 Upstream tension roller 6, 26, 36 Downstream tension roller 7 Bottom plate 8 Support member 9 Air ejection part 10, 20, 30 Sheet conveying apparatus 31 Moving mechanism 32 Cam 33, 37 Spring 34, 38 Restricting member

JP 2010-89887 A

Claims (5)

A suction belt that is stretched by a plurality of stretching rollers and is disposed opposite to the upper surface of the sheet bundle on which the sheets are stacked, and moves endlessly;
An air ejection means for ejecting air from the downstream end portion in the sheet conveying direction toward the sheet bundle and floating and separating the sheet;
Adsorbing means for adsorbing the uppermost sheet that has been levitated and separated to the adsorbing belt by electrostatic force;
In the sheet conveying apparatus that conveys the uppermost sheet by endless movement of the adsorption belt after adsorbing the uppermost sheet floated and separated to the adsorption belt,
The stretch surface facing the upper surface of the sheet bundle of the suction belt is inclined so that the upstream side in the sheet conveying direction is higher than the downstream side in the sheet conveying direction when air is ejected by the air ejecting means. Sheet transport device. In the sheet conveying apparatus according to claim 1,
A sheet conveying apparatus, wherein a diameter of a stretching roller on the most upstream side in the sheet conveying direction among a plurality of stretching rollers is smaller than a diameter of a stretching roller on the most downstream side in the sheet conveying direction. In the sheet conveying apparatus according to claim 1 or 2,
A tension roller moving means for moving the position of the tension roller;
The stretching roller moving means moves the stretching roller when air is blown by the air blowing means according to the type of sheet. In the sheet conveying apparatus according to claim 3,
A pair of conveyance rollers for conveying the sheet separated from the suction belt,
The stretching roller moving means is configured so that after the uppermost sheet is attracted to the suction belt, the nip of the conveying roller pair is on a plane having a stretching surface facing the upper surface of the sheet bundle of the suction belt. A sheet conveying apparatus characterized by moving a tension roller. In an image forming apparatus comprising: an image forming unit that forms an image on a sheet; and a sheet conveying unit that separates the uppermost sheet from the stacked sheet bundle and conveys the sheet to the image forming unit.
An image forming apparatus using the sheet conveying device according to claim 1, 2, 3, or 4 as the sheet conveying means.

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