JP2006273509A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of shortening a sheet transporting path. <P>SOLUTION: The image forming apparatus is equipped with a sheet sensing means 20 to sense a sheet with rotation of a rotary member 22 rotating being pressed by the sheet and a plurality of sheet transporting paths, and between the sensing means 20 and the transporting paths a changeover means 21 rotatable is installed which rotates in conformity to a signal given by the sheet sensing means 20 and changes over the path into the prescribed one of the mentioned sheet transporting paths. The changeover means 21 is furnished in its position confronting the rotary member 22 with a cutout 26 to allow the rotary member 22 to pass through when it rotates, which enables the sheet sensing means 20 to be installed in the neighborhood of the changeover means 21. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an apparatus having a plurality of sheet conveyance paths.

  Conventionally, image forming apparatuses such as computer printers, copiers, and printing machines use electrophotographic technology that electrostatically controls and adsorbs developer made of fine powder, or performs ink spraying, offset printing, and the like. Some use it to form an image.

  For example, in the case of an image forming apparatus using electrophotographic technology, when forming an image, an electrostatic latent image is first formed on the surface of a photosensitive drum or a photosensitive belt, which is an image carrier, and the electrostatic latent image is formed. A visible image is developed by developing with toner as a developer. Next, after the developed toner image is transferred onto a sheet by a transfer device, the sheet is heated and pressed by a fixing device to fix the toner image on the sheet, thereby forming an image.

  By further applying this technique and using a plurality of color developers, it is possible to obtain a plurality of color images. In principle, by using yellow, magenta, and cyan developers, a full-color image can be obtained by mixing colors using a black developer in addition to these three types of developers.

  In the case of an image forming apparatus that uses ink / pigment, an image can be obtained by applying ink / pigment to a sheet in a place corresponding to a document (regardless of substance or image data). In addition, there is a method of spraying ink by applying physical compression to a minute nozzle containing ink or repeating generation and disappearance of bubbles in the nozzle. Also, in offset printing, ink is applied to the underlay to transfer the ink to the sheet. That is, in the case of an image forming apparatus using ink / pigment, a full color image can be obtained by using ink / pigment of yellow, magenta, cyan (black and other colors are added as appropriate) in any method. it can.

  By the way, in such an image forming apparatus, in addition to a mode (function) for forming an image on one side of a sheet, when two or more copies of a document composed of a plurality of pages are printed, a plurality of sheets are stacked in order of the pages of each document. There are a sort mode for distributing to a place, a stapling mode for bundling and fixing a document composed of a plurality of pages, and a duplex mode for forming an image on the back side of a sheet on which an image is formed on one side.

  In such an image forming apparatus, in accordance with these modes, in addition to a sheet conveyance path for conveying a sheet having an image formed on one side to the sheet stacking unit, two or more copies of a document composed of a plurality of pages are printed. In such a case, the sheet transport path for sending the documents one by one to the plurality of stacking locations in order of the pages (or the finisher), or the stapler section for bundling and fixing the documents consisting of a plurality of pages. In order to form an image on the back side of a sheet having a sheet conveyance path and an image formed on one side, a sheet conveyance path is provided for reversing the front and back of the sheet and guiding the sheet upstream again.

  Here, when a plurality of sheet conveyance paths are provided as described above, the sheet conveyance path is selected upstream of the sheet conveyance path to direct the sheet to one of the plurality of sheet conveyance paths according to the mode. Therefore, switching means for switching the sheet to guide the sheet to a predetermined sheet conveyance path is required.

  For example, in a conventional image forming apparatus, double-sided printing and multiple printing are performed downstream of a sheet conveying path that leads a sheet to a sheet post-processing apparatus downstream of a fixing device, a sheet conveying path that leads to a duplex printing tray, and a duplex printing tray. In such an image forming apparatus, a switching unit is provided between the fixing device and the sheet conveyance path, and the switching unit allows the sheet to be conveyed in a predetermined sheet conveyance direction. It is led to the passage.

  Further, another switching unit for selectively performing duplex printing and multiple printing is provided downstream of the duplex printing tray, and the sheet is guided to a specific sheet conveyance direction and sheet conveyance path by the other switching unit. (For example, refer to Patent Document 1). As described above, when functions are added to the image forming apparatus, a plurality of sheet conveyance paths are required, and as a result, a switching unit is required.

  On the other hand, in order to obtain a good image in the image forming apparatus, it is necessary to accurately grasp the start of image printing and the sheet conveyance timing. If the sheet conveyance timing is deviated, there may be a problem that the leading edge margin of the sheet becomes too large or the image protrudes from the sheet. In addition, if the operation timing of the sheet post-processing apparatus downstream of the image forming apparatus is shifted, there is a problem that the sheet is damaged or the sheet stays, such as a jam.

  For this reason, conventionally, a sheet detection unit for detecting the leading edge of the sheet and the presence or absence of the sheet is provided at a predetermined position, and the position of the sheet in the image forming apparatus is grasped or passed by the sheet detection unit. I am doing so. Here, as such a sheet detection means, for example, a light emitting part and a light receiving part of light of a certain wavelength (including invisible light) are provided, the light receiving part is shielded as the sheet passes, and the reaction of the light receiving part at this time There is one that detects the sheet using the change.

  In such a sheet detection means, when the sheet itself is passed between the light emitting unit and the light receiving unit or a mechanism such as a link member is used and the sheet hits the link member, the link member moves, and the link There is a configuration in which a part of the member is interposed between the light emitting unit and the light receiving unit, and as a result, the light receiving unit is shielded to detect passage of the sheet.

  Incidentally, the switching operation of the switching means may be performed by detecting a sheet. In such a case, it is necessary to dispose the sheet detecting means in the vicinity of the switching means.

  FIG. 7 is a view showing such a switching means and a sheet detecting means arranged in the vicinity of the switching means. In FIG. 7, 121 is a flapper as a switching means, and this flapper 121 has a shaft 129 as a fulcrum. And a guide surface 121a for guiding the sheet over the entire sheet width direction.

  Reference numeral 120 denotes a sheet detecting unit disposed in the vicinity of the flapper 121. The sheet detecting unit 120 includes a sensor unit 125 including a light emitting unit and a light receiving unit (not shown), and a sensor as the shaft 123 rotates. A shielding portion 124 that enters or leaves between the light emitting portion and the light receiving portion of the portion 125, and a contact member 122 that is attached to the shaft 123 and that is pressed by the sheet and pivots up and down about the shaft 123 as a fulcrum. ing.

  Then, when the contact member 122 is pressed by the sheet S conveyed from the direction of arrow A shown in FIG. 8A and pivots upward about the shaft 123 shown in FIG. The shielding portion 124 rotates integrally with the shaft 123 to exit from between the light emitting portion and the light receiving portion of the sensor portion 125, and the passage of the sheet S can be detected from the change in the signal of the sensor portion 125 at this time. it can.

  When the sheet detection unit 120 detects the passage of the sheet S in this way, the flapper 121 does not rotate, for example, when the sheet S is conveyed in the direction of arrow B shown in FIG. Thereby, the sheet S is conveyed in the arrow B direction as it is.

  On the other hand, when the sheet is conveyed in the direction of arrow C shown in FIG. 9, the flapper 121 rotates downward about the shaft 129. As a result, the sheet S is guided along the guide surface 121a of the flapper 121 thus rotated downward, and is conveyed in the direction of arrow C. When guiding the sheet S in this way, the flapper 121 exists over the entire width of the sheet S in order to reliably guide the sheet S.

Japanese Patent Laid-Open No. 06-015980

  By the way, in the conventional image forming apparatus in which the sheet detecting unit 120 is arranged in the vicinity of the flapper 121 as described above, when the flapper 121 and the contact member 122 come close to each other, the sheet S is detected or the sheet conveyance path is switched. Therefore, it is necessary to dispose the flapper 121 and the detection contact member 122 at a predetermined distance so that the rotation trajectories of the flapper 121 and the contact member 122 do not overlap each other.

  However, when the flapper 121 and the contact member 122 are arranged apart from each other as described above, the flapper 121 and the sheet detection unit 120 are arranged in series on the sheet conveyance path. There is a problem that the image forming apparatus main body and the system become large due to lengthening.

  Accordingly, the present invention has been made in view of such a current situation, and an object thereof is to provide an image forming apparatus capable of shortening a sheet conveyance path.

  The present invention provides an image forming apparatus that includes a plurality of sheet conveyance paths and selectively conveys a sheet to a predetermined sheet conveyance path among the plurality of sheet conveyance paths. A rotating member, and a sheet detecting means for detecting a sheet by the rotation of the rotating member; and a rotatable member provided between the sheet detecting means and the plurality of sheet conveying paths. Switching means for switching to a predetermined sheet conveying path, and a notch that allows passage of the rotating member is formed at a position of the switching means facing the rotating member of the sheet detecting means. It is what.

  According to the present invention, a sheet conveyance path is disposed between a plurality of sheet conveyance paths between a sheet detection unit that detects a sheet by rotation of a rotation member that is rotated by being pressed by the sheet, and the plurality of sheet conveyance paths. The switching means for switching to the predetermined sheet conveying path is provided so as to be rotatable, and a notch portion that allows passage of the rotating member is formed at a position facing the rotating member of the sheet detecting means of the switching means. The sheet detecting means can be provided in the vicinity of the switching means, whereby the sheet conveyance path can be shortened.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is an overall configuration diagram of a color laser printer as an example of an image forming apparatus according to a first embodiment of the present invention.

  In the figure, reference numeral 50 denotes a color laser printer, and 51 denotes a color laser printer main body (hereinafter referred to as a printer main body). A paper unit 8, a sheet conveying device 9 that conveys a sheet fed from the paper feeding unit 8 to the image forming unit 52, and a fixing device 10 that fixes an image formed on the sheet are provided.

  Here, the image forming unit 52 is arranged in the vertical direction, and each of the photosensitive drums 1a to 1d and the photosensitive drums 1a to 1d, which are image carriers that support toner images of four colors of yellow, magenta, cyan, and black. Charging means 2a to 2d, which are arranged around 1d along the rotation direction and uniformly charge the surface of the photosensitive drum, and irradiate a laser beam based on image information to form an electrostatic latent image on the photosensitive drum. Exposing means 3a to 3d for forming the toner, developing means 4a to 4d for making the toner image adhere to the electrostatic latent image and developing the toner image, and cleaning means 6a to 6a for removing the toner remaining on the surface of the photosensitive drum after transfer. 6d etc. are provided.

  In this embodiment, the photosensitive drums 1a to 1d, the charging units 2a to 2d, the developing units 4a to 4d, and the cleaning units 6a to 6d are integrally formed as a cartridge to form process cartridges 7a to 7d. Yes.

  Further, the charging means 2a to 2d are conductive rollers, which are brought into contact with the surface of the photosensitive drum and charged with a charging bias voltage by a power source (not shown) to uniformly charge the surface of the photosensitive drum. It is what The exposure means 3a to 3d have a polygon mirror, and image light corresponding to an image signal is irradiated to the polygon mirror from a laser diode (not shown).

  Also, transfer means 5a to 5d for holding the transfer conveyance belt 9a together with the four photosensitive drums 1a to 1d are provided inside the transfer conveyance belt 9a which is an endless sheet conveyance member for conveying a sheet to be described later. Has been.

  Here, the transfer units 5a to 5d are connected to a power supply for transfer bias (not shown), and positive charges are applied from the transfer units 5a to 5d to the sheet via the transfer conveyance belt 9a. Yes. By applying the transfer bias in this way, the negative color toner images on the photosensitive drum are sequentially transferred onto the sheet in contact with the photosensitive drums 1a to 1d, so that a multicolor image is formed. It has become.

  The feeding unit 8 includes a paper feeding cassette 8a, a multi feeding tray 8b, a multi feeding unit 8c, a registration roller pair 8d, and the like. Here, the paper feed cassette 8a stores a plurality of sheets and is loaded on the bottom of the printer main body, and the multi-feed tray 8b is usually stored in the front of the printer main body, but when used, FIG. It is opened as shown in Fig. 2 and a plurality of sheets are stacked.

  When forming an image, the sheet is separated and fed one by one from the sheet feeding cassette 8a by the pickup roller 8a1, and the sheet conveying device 9 is conveyed by the intermediate conveying roller 8a2 and the registration roller pair 8d that conveys the sheet at a predetermined timing. It is designed to be conveyed.

  When feeding sheets from the multi-feed tray 8b, the sheets stored in the multi-feed tray 8b are separated and fed one by one by the multi-pickup roller 8c1, and the multi-conveying roller 8c2 and the registration roller pair 8d are fed. Is conveyed to the sheet conveying device 9.

  The sheet conveying device 9 includes a transfer conveying belt 9a as a sheet carrier that is stretched and supported by a driving roller 9b and driven rollers 9c to 9e and is disposed to face all the photosensitive drums 1a to 1d. ing. Here, the transfer conveyance belt 9a electrostatically attracts the sheet to the outer peripheral surface facing the photosensitive drums 1a to 1d, and circulates and moves by the driving roller 9b so that the sheet contacts the photosensitive drums 1a to 1d. It is like that. The sheet is conveyed to the transfer position by the transfer conveyance belt 9a by being electrostatically attracted to the transfer conveyance belt 9a that circulates in this way, and the toner image on the photosensitive drum 1 is transferred.

  Reference numeral 9f denotes an adsorption roller that is disposed at the most upstream position of the transfer conveyance belt 9a, holds the sheet together with the transfer conveyance belt 9a, and adsorbs the sheet to the transfer conveyance belt 9a. By applying a voltage to the roller 9f, an electric field is formed between the opposed driven roller 9c and a dielectric polarization is generated between the transfer conveyance belt 9a and the sheet, thereby electrostatically attracting both. It is supposed to give rise to.

  The fixing device 10 applies heat and pressure to the image formed on the sheet to fix the toner image, and includes a fixing belt 10a and an elastic pressure roller 10b. Here, the fixing belt 10a is a cylindrical belt having an electromagnetic induction heat generating layer, and is guided by a belt guide member 10c having a built-in magnetic field generating means including an exciting coil and a T-shaped magnetic core.

  The elastic pressure roller 10b sandwiches the fixing belt 10a and forms a fixing nip portion N having a predetermined width with a predetermined pressure contact force with the belt guide member 10c. Then, the elastic pressure roller 10b is driven to rotate by a driving means (not shown), and the cylindrical fixing belt 10a is rotated accordingly, and electromagnetic induction heat generation of the fixing belt 10a is performed by feeding power from an excitation circuit (not shown) to the excitation coil. It has become so.

  Next, an image forming operation of the color laser printer 50 configured as described above will be described.

  First, when the surface of the photosensitive drums 1a to 1d uniformly charged by the charging units 2a to 2d is scanned with a laser beam corresponding to the image information irradiated from the exposure units 3a to 3d, A latent image is formed, and this latent image is further developed by developing means 4a to 4d, whereby toner images of four colors of yellow, magenta, cyan and black are formed on the surface of the photosensitive drum.

  In parallel with this toner image forming operation, the sheet accommodated in the paper feed cassette 8a is picked up by the pickup roller 8a1, or the sheet accommodated in the multi-feed tray 8b is fed by the multi-pickup roller 8c1. After being separated and fed one by one, after being guided to the registration roller pair 8d, the registration roller pair 8d is attracted to the transfer conveyance belt 9a in synchronism with the image forming operation, and is transferred to the photosensitive drums 1a to 1d. The belt 9a is conveyed to a transfer portion where the belt 9a is in pressure contact.

  Next, with respect to the sheet conveyed to the transfer unit in this way, each color on the photosensitive drums 1a to 1d is acted on by the transfer means 5a to 5d which are arranged in each transfer unit and to which a voltage having a polarity opposite to that of the toner is applied. The toner images are sequentially transferred onto the sheet. The sheet on which the four color toner images are transferred in this way is separated from the transfer conveyance belt 9a and conveyed to the fixing device 10.

  Next, the sheet on which the unfixed toner image conveyed from the image forming unit 52 is formed is elastic with the fixing belt 10a of the fixing nip N in a state where the temperature of the fixing nip N rises to a predetermined temperature. It is introduced between the pressure roller 10b and the image surface facing upward, that is, facing the fixing belt surface. Thereafter, the image surface is brought into close contact with the outer surface of the fixing belt 10a at the fixing nip portion N and together with the fixing belt 10a. The fixing nip portion N is nipped and conveyed.

  In the process of being conveyed along the fixing nip N together with the fixing belt 10a in this way, the sheet is heated by electromagnetic induction heat generated by the fixing belt 10a, and the unfixed toner image on the sheet is heated and fixed. As a result, a full-color print image is fixed on the sheet as a permanent image. Next, after the full color print image is fixed as a permanent image in this way, the sheet S is discharged and stacked on the discharge tray 13 by the discharge roller pairs 11 and 12.

  By the way, the color laser printer 50 according to the present embodiment is capable of forming images on both sides of a sheet, and when forming images on both sides of a sheet, as shown in FIG. The sheet reversing device 30A is configured to be detachably mounted downstream of the discharge roller pair 11 and 12 of the printer main body 51.

  Here, the sheet reversing device 30 </ b> A is disposed downstream of the discharge roller pair 11 and 12 and the sheet reversing unit 30 that reverses the sheet discharged from the discharge roller pair 11 and 12 when forming images on both sides of the sheet. The flapper 21, the reversing roller pair 31, and the re-conveying roller pair 32 are provided.

  Here, when an image is formed only on one side of the sheet, the flapper 21 is at a position that does not hinder the discharge of the sheets discharged from the roller pairs 11 and 12 provided in the sheet discharge path R1, as shown in FIG. However, in the double-side mode in which images are formed on both sides of the sheet, it is rotated downward. Then, the flapper 21 serving as the switching means rotates downward in this way, so that the sheet conveyance path is switched from the sheet discharge path R1 to the reverse conveyance path R2, and thereby the sheet S is guided to the sheet reversing unit 30; Thereafter, the sheet is conveyed again into the printer main body by the reverse rotation of the reverse roller pair 31 and the reconveying roller pair 32.

  In FIG. 2, reference numeral 32 denotes a re-conveying path into which a sheet conveyed by the reversing roller pair 31 and the re-conveying roller pair 32 is fed after 15 is reversed. The sheet conveyed to the re-conveying path 15 is After passing through the oblique feeding rollers 16a and 16b attached to the front surface of the printer main body, the paper is conveyed to the U-turn roller 17 and again conveyed to the image forming unit 52 by the U-turn roller 17 and the registration roller 8d. ing.

  That is, in the color laser printer 50 of the present embodiment, not only the sheet carrying the image on one side is directly discharged to the paper discharge tray 13 but also the image carrying the image on one side by the flapper 21. By selectively switching the sheet conveyance path with respect to the sheet, the sheet surface is automatically reversed and conveyed again to the image forming unit 52, and an image is formed on the surface opposite to the printing surface of the sheet. There is a function.

  When an image is formed on the surface opposite to the printing surface of the sheet as described above, the sheet on which the single-sided image is fixed is loaded on the discharge tray 13 in order to carry the image on both sides of the sheet. The sheet conveyance path is changed by the flapper 21 without being conveyed, and is guided to the reverse conveyance path R2.

  By the way, in the upstream of the flapper 21 that switches the sheet conveyance path in this way, specifically, a sheet conveyed is detected between the fixing device 10 and the sheet discharge tray 13 as shown in FIG. A sheet detection unit 20 is provided for identifying whether or not the sheet conveyance has been performed normally. Based on the signal from the sheet detection means 20, the printer main body 51 or a control unit (not shown) provided outside adjusts the operation timing of the printer main body 51 and makes a jam determination. .

  In the present embodiment, the sheet detection means 20 includes a sensor unit 25 having a light emitting unit and a light receiving unit (not shown), for example, provided with a photo interrupter, and a sensor unit 25 as the shaft 23 rotates. A shielding portion 24 that enters or leaves between the light emitting portion and the light receiving portion; and a contact member 22 that is attached to the shaft 23 and is a rotating member that is pressed by the sheet and pivots up and down about the shaft 23 as a fulcrum. It has.

  In the sheet detection means 20, when the contact member 22 is pressed by the sheet and pivots upward about the shaft 23, the shielding unit 24 rotates together with the shaft 23, and the sensor unit 25 The sheet exits between the light emitting unit and the light receiving unit, and the passage of the sheet can be detected from the change in the signal of the sensor unit 25 at this time.

  In FIG. 3, reference numeral 26 denotes a cutout portion formed at a position facing the contact member 22 of the flapper 21. By forming the cutout portion 26 at such a position, the contact member 22 is pressed against the sheet. Even in this case, the flapper 21 does not hinder the rotation of the contact member 22. That is, the contact member 22 can pass through.

  Thereby, the contact member 22 (sheet | seat detection means 20) can be arrange | positioned close to the flapper side. In addition, when such a notch part 26 is formed, the width of the notch part 26 with respect to the width of the notch part 26 so that the sheet is guided along the guide surface 21a of the flapper 21 without being caught by the notch part 26. It is preferable to make the width sufficiently wide.

  Then, by forming the notch portion 26 in the flapper 21 in this way, the sheet S is conveyed from the arrow direction A as shown in FIG. 4A and comes into contact with the contact member 22. 4 (b), the contact member 22 is pressed upward by the sheet S and pivots upward about the shaft 23. At this time, the flapper 21 has a notch 26, so the contact member The 22 rotation trajectories and the flapper 21 can be overlapped. Thereby, the contact member 22 can pass through the notch 26 of the flapper 21.

  In order to convey the sheet toward the sheet reversing unit 30 (see FIG. 2), when the flapper 21 rotates downward to change the conveyance direction of the sheet S to the arrow C direction as shown in FIG. The vertical positional relationship between the contact member 22 and the contact member 22 is reversed with respect to the normal state. However, when the flapper 21 rotates downward as described above, the notch 26 is formed in the flapper 21. The contact member 22 does not prevent the flapper 21 from rotating.

  In this way, the sheet detection means 20 rotates between the sheet discharge path R1 and the reverse conveyance path R2, which are a plurality of sheet conveyance paths in the present embodiment, based on the signal from the sheet detection means 20, A flapper 21 that switches the sheet conveyance path to a predetermined sheet conveyance path is rotatably provided, and when the contact member 22 rotates to a position facing the contact member 22 of the sheet detection means 20 of the flapper 21, By forming the cutout portion 26 that allows passage, the sheet detection means 20 can be provided in the vicinity of the flapper 21, thereby shortening the sheet conveyance path.

  Further, by providing the sheet detection means 20 in the vicinity of the flapper 21 in this way, it is possible to know the sheet existence timing at the flapper 21, thereby comparing with the case where the sheet detection means 20 is provided at a distant position. Thus, the timing of the constituent devices downstream of the flapper 21 can be accurately grasped. For example, when switching between single-sided printing and double-sided printing, the double-sided printing timing can be grasped, so that the image transfer timing shift can be reduced, and a good image can be obtained.

  Further, since the sheet conveyance path is shortened, the conveyance time itself is shortened, so that the sheet can be discharged more quickly, and the waiting time for printed output of the user can be reduced. Furthermore, since the sheet conveyance path is shortened, the printer main body 51 can be made small, and the restrictions when installing the color laser printer 50 can be reduced.

  Further, when the sheet reversing device 30A is mounted above the discharge tray as in the present embodiment, the sheet reversing device 30A covers the upper side of the paper discharge tray 13. Even in this case, the sheet conveyance path is shortened. By this, the sheet | seat discharged | emitted on the discharge tray can be exposed more, and sheet visibility can be improved by this.

  Next, a second embodiment of the present invention will be described.

  6 is an enlarged view of a main part of the image forming apparatus according to the present embodiment. In FIG. 6, the same reference numerals as those in FIG. 4 indicate the same or corresponding parts.

  In FIG. 6, 22A is a contact member of the sheet detecting means 20, and when the sheet S is conveyed from the direction of arrow A shown in FIG. It is designed to rotate. Then, the sheet detecting means 20 detects the presence or absence of the sheet S by such upward rotation of the contact member 22A.

  On the other hand, when the sheet S passes, the contact member 22A rotates downward due to its own weight, and comes into contact with the stacked sheets Sa on the paper discharge tray 13 as shown in FIG. The amount (height) of the stacked sheets Sa on the discharge tray 13 which is a discharge sheet stacking unit is detected by detecting the angle of the contact member 22A by the sensor unit 25 (see FIG. 3) or another sensor. be able to.

  In the present embodiment, the height of the stacked sheets Sa reaches a certain amount, and as shown in FIG. 6B, the position of the contact member 22A is the same as the presence of the conveying sheet, and this state is the sheet. If it is longer than the conveyance contact time, a control unit (not shown) determines “abnormal” and stops conveying the sheet. As a result, the sheet discharge passage R1 can be prevented from being blocked by the sheet.

  In other words, according to the present embodiment, it is possible to detect the sheet S and the stack amount of discharged sheets by the single sheet detecting unit 20. Even in such a configuration, the sheet conveyance path can be shortened by providing the notch 26 in the flapper 21.

  In the above description, the case where the sheet reversing device 30A is mounted on the printer main body 51 has been described. However, the present invention is not limited to this, and for example, a multi-stage where sheets are finally stacked on the side of the printer main body 51. A sheet post-processing apparatus having a tray and configured to stack one sheet per tray when a plurality of sheets of the same image are discharged may be installed.

  Even when such a sheet post-processing apparatus that distributes sheets is installed, the flapper 21 having the above-described configuration is used to move the sheet toward the sheet post-processing apparatus and the sheet discharge tray 13. Switching to the sheet discharge passage for guiding the sheet may be performed.

1 is an overall configuration diagram of a color laser printer that is an example of an image forming apparatus according to a first embodiment of the present invention. FIG. The figure which shows the state which attached the sheet inversion apparatus to the said color laser printer FIG. 3 is a perspective view showing a flapper and sheet detection means provided in the color laser printer. The figure which shows the operation | movement at the time of sheet conveyance of the said sheet | seat detection means. The figure which shows the sheet | seat conveyance path switching operation | movement of the said flapper. The principal part enlarged view of the image forming apparatus which concerns on the 2nd Embodiment of this invention. The perspective view which shows the conventional flapper and sheet | seat detection means. The figure which shows the operation | movement at the time of sheet conveyance of the said conventional sheet detection means. The figure which shows the sheet conveyance path switching operation | movement of the said conventional flapper.

Explanation of symbols

13 Paper discharge tray 20 Sheet detection means 21 Flapper 22 Contact member 22A Contact member 24 Shielding part 25 Sensor part 26 Notch part 30A Sheet reversing device 50 Color laser printer 51 Printer main body 52 Image forming part R1 Sheet discharge path R2 Reverse conveyance path S Sheet

Claims (6)

In an image forming apparatus comprising a plurality of sheet conveyance paths, wherein the sheet is selectively conveyed to a predetermined sheet conveyance path among the plurality of sheet conveyance paths,
A sheet detecting means that includes a rotating member that is rotated by being pressed by the sheet, and that detects the sheet by the rotation of the rotating member;
A switching means that is rotatably provided between the sheet detection means and the plurality of sheet conveyance paths, and switches the sheet conveyance path to the predetermined sheet conveyance path;
With
2. An image forming apparatus according to claim 1, wherein a notch portion that allows passage of the rotating member is formed at a position facing the rotating member of the sheet detecting unit of the switching unit. One of the plurality of sheet conveyance paths is a sheet discharge path that is provided downstream in the sheet conveyance direction of the switching unit and discharges the sheet,
A discharge sheet stacking section for stacking sheets discharged from the sheet discharge passage;
2. The image forming apparatus according to claim 1, wherein the height of the sheets stacked on the discharged sheet stacking unit is detected by a rotating member of the sheet detecting unit.   3. The sheet stacking unit according to claim 2, wherein a rotation member of the sheet detection unit is brought into contact with a sheet stacked on the discharge sheet stacking unit, and a stacked sheet height is detected based on an angle of the rotation member. Image forming apparatus.   4. The image forming apparatus according to claim 1, wherein the plurality of sheet conveyance paths include a reversing path for reversing the sheet to form an image on both sides of the sheet. 5.   The image forming apparatus according to claim 4, wherein a reversing unit including the reversing passage is detachably provided. 4. The image forming apparatus according to claim 1, wherein the plurality of sheet conveyance paths include a sheet conveyance path that directs the sheet to a sorting device that sorts the sheets. 5.

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