JP2009186763A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which is capable of outputting a high-quality image by making the transferability of a toner image excellent, without contaminating a paper with toner. <P>SOLUTION: The image forming apparatus 1 including: a photoreceptor drum 32; an image forming section 30a; a transfer section 30; and a pretransfer paper guide 24 which is arranged at a predetermined interval from the surface of the photoreceptor drum 32 and guides the paper to the transfer section 30 includes: a pretransfer paper guide displacement means 25 which selectively displaces the pretransfer paper guide 24 between a position where the pretransfer paper guide 24 gets close to the photoreceptor drum 32 and a position where the pretransfer paper guide 24 is away from the photoreceptor drum 32; and a sub-control section 60 which controls driving of the pretransfer paper guide displacement means 25. The sub-control section 60 controls driving of the pretransfer paper guide displacement means 25, so as to displace the pretransfer paper guide 24 to the position where the pretransfer paper guide 24 is away from the photoreceptor drum 32, while an image is formed on the surface of the photoreceptor drum 32 and when the paper is not conveyed to the pretransfer paper guide 24. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that transfers a toner image formed on a photosensitive drum by an electrophotographic method to a recording medium and outputs it.

  2. Description of the Related Art Conventionally, electrophotographic image forming apparatuses such as copying machines, printers, facsimiles, and the like use a so-called direct transfer method in which a toner image is formed on a photosensitive drum and the toner image is directly transferred to a sheet (recording medium). An output image is obtained, or the toner image is temporarily transferred from a photosensitive drum to an intermediate transfer belt (intermediate transfer medium) and then transferred from the intermediate transfer belt to paper again, so that an output image is obtained by so-called indirect transfer. It has been known.

  In the image forming apparatus that employs the direct transfer method among the transfer methods described above, a guide member (hereinafter referred to as “pre-transfer guide member”) that guides the sheet conveyed to the photosensitive drum to the position immediately before the photosensitive drum is provided. Thus, the paper is accurately conveyed to the photosensitive drum.

  In the image forming apparatus configured as described above, in order to improve the transferability of the toner image from the photosensitive drum to the sheet, it is necessary to bring the pre-transfer guide member close to the photosensitive drum. However, when the pre-transfer guide member is in the vicinity of the photosensitive drum, if an image is formed on the photosensitive drum in a non-sheet-passing state where the paper is not conveyed to the pre-transfer guide member, the image remains on the photosensitive drum. Since the toner is released and adheres to the pre-transfer guide member, there is a problem that the toner is smeared on the back side of the sheet guided and conveyed by the pre-transfer guide member.

Therefore, as a countermeasure against the above problem, it is necessary to separate the pre-transfer guide member from the photosensitive drum. In the prior art, there is disclosed a technique in which damage to the photosensitive drum is prevented by separating the pre-transfer guide member when the apparatus is not in operation (see Patent Document 1).
JP 2002-296862 A

  However, when the pre-transfer guide member is separated from the photosensitive drum as in the above prior art, there arises a problem that transferability is lowered. As described above, conventionally, it has been difficult to satisfy both of the requirements of improving toner image transferability without causing toner contamination on the back of the paper.

  The present invention has been made in view of the above-described conventional problems. When a toner image is transferred to a sheet, the toner image is not smudged on the sheet, and the transfer property of the toner image is improved and the quality is improved. An object of the present invention is to provide an image forming apparatus capable of realizing image output.

The configuration of the image forming apparatus according to the present invention for solving the above-described problems is as follows.
The present invention includes a photosensitive drum on which an electrostatic latent image is formed and a toner image is formed based on the electrostatic latent image, an image forming unit that forms an electrostatic latent image on the surface of the photosensitive drum, A transfer unit that transfers the toner image formed on the photosensitive drum to the conveyed recording medium, and a pre-transfer that is arranged at a predetermined interval with respect to the surface of the photosensitive drum and guides the recording medium to the transfer unit. In an image forming apparatus that includes a guide member and transfers and outputs a toner image formed on the surface of the photosensitive drum by electrophotography on a recording medium, the pre-transfer guide member is positioned close to the photosensitive drum And a pre-transfer guide member displacing means for selectively displacing to a position separated from the photosensitive drum, and a control unit for controlling driving of the pre-transfer guide member displacing means, and the control unit at least When the image forming unit is forming an image on the surface of the photosensitive drum and the recording medium is not conveyed to the pre-transfer guide member, the transfer member is displaced so as to be moved away from the photosensitive drum. The drive of the front guide member displacing means is controlled.

  In the present invention, the pre-transfer guide member displacing unit is energized by the control unit so that the pre-transfer guide member displacing unit displaces the pre-transfer guide member to a position separated from the photosensitive drum. It is preferable to make it.

  The present invention further includes a pre-transfer guide member regulating member that regulates a distance between the pre-transfer guide member and the photoconductive drum when the pre-transfer guide member is displaced to a position close to the photoconductive drum. Is preferred.

  In the present invention, the pre-transfer guide member is separated from the photoconductive drum by 0.6 to 1.0 mm at a position where the distance between the pre-transfer guide member and the photoconductive drum is close to the photoconductive drum. It is preferable to set it to be 1.5 mm or more at the position.

  The present invention further comprises a recording medium detecting means for detecting a recording medium conveyed to the pre-transfer guide member on a recording medium conveyance path upstream of the pre-transfer guide member in the recording medium conveyance direction. The detection means detects the upstream end of the recording medium to be conveyed in the recording medium conveyance direction, that is, the trailing edge of the recording medium, and the control unit conveys the recording medium detected by the recording medium detection means. It is preferable to control driving of the pre-transfer guide member displacing means so that the pre-transfer guide member is displaced to a position separated from the photosensitive drum based on the passage timing of the upstream end in the direction.

  According to the present invention, a photosensitive drum on which an electrostatic latent image is formed and a toner image is formed based on the electrostatic latent image, and an image forming unit that forms an electrostatic latent image on the surface of the photosensitive drum; A transfer unit that transfers a toner image formed on the photosensitive drum to a conveyed recording medium, and a recording medium that is disposed at a predetermined interval with respect to the surface of the photosensitive drum and guides the recording medium to the transfer unit. In an image forming apparatus that includes a pre-transfer guide member and transfers and outputs a toner image formed on the surface of the photoconductive drum onto a recording medium by an electrophotographic method, the pre-transfer guide member is close to the photoconductive drum A pre-transfer guide member displacing means for selectively displacing the position to a position separated from the photosensitive drum, and a control unit for controlling the drive of the pre-transfer guide member displacing means. When When the image forming unit is forming an image on the surface of the photosensitive drum and the recording medium is not conveyed to the pre-transfer guide member, the pre-transfer guide member is displaced to a position away from the photoconductive drum. By controlling the driving of the pre-transfer guide member displacing means, it is possible to suppress the toner from adhering to the pre-transfer guide member due to the release of the toner remaining on the photosensitive drum during image formation in the image forming unit. Therefore, the toner guided to the pre-transfer guide member does not cause toner contamination, and the pre-transfer guide member can be brought close to the photosensitive drum during transfer, so that the transferability of the toner image can be improved. High-quality image output can be realized.

  Further, according to the present invention, the pre-transfer guide member displacing means causes the pre-transfer guide member displacing means to move the pre-transfer guide member through the energization of the pre-transfer guide member displacing means (for example, a solenoid or a drive motor). Since the guide member is displaced to a position separated from the photosensitive drum, the pre-transfer guide member can be displaced with a simple configuration.

  According to the invention, the pre-transfer guide member regulating member that regulates the interval between the pre-transfer guide member and the photoconductive drum when the pre-transfer guide member is displaced to a position close to the photoconductive drum. By providing, the guide member before transfer can be reliably arranged at a predetermined position with a simple configuration.

  According to the present invention, the pre-transfer guide member may be 0.6 to 1.0 mm at a position where the distance between the pre-transfer guide member and the photoconductive drum is close to the photoconductive drum. By setting the distance to be 1.5 mm or more at a position away from the sheet, the sheet can be stably conveyed in a state where the guide member before transfer is close to the photosensitive drum. It is possible to suppress adhesion of toner remaining on the photosensitive drum in a state of being separated from the photosensitive drum.

  According to the present invention, the recording medium detection means for detecting the recording medium conveyed to the pre-transfer guide member is provided on the recording medium conveyance path upstream of the pre-transfer guide member in the recording medium conveyance direction, The upstream end of the recording medium in the recording medium conveyance direction, that is, the rear end of the recording medium is detected by the recording medium detection means, and the control unit records the recording medium detected by the recording medium detection means. By controlling the drive of the pre-transfer guide member displacing means so that the pre-transfer guide member is displaced to a position separated from the photoconductor drum based on the passage timing of the upstream end portion in the medium conveyance direction, the photoconductor It is possible to minimize the toner remaining on the drum from adhering to the pre-transfer guide member.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an explanatory diagram showing the overall configuration of an image forming apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment includes a photosensitive drum 32 on which an electrostatic latent image is formed and a toner image is formed based on the electrostatic latent image. An image forming unit 30 a that forms an electrostatic latent image on the surface, a transfer unit 30 that transfers a toner image formed on the photosensitive drum 32 to a conveyed paper (recording medium), and the surface of the photosensitive drum 32 And a pre-transfer paper guide (pre-transfer guide member) 24 that is disposed at a predetermined interval and guides the paper to the transfer unit 30. The toner image formed on the surface of the photosensitive drum 32 by the electrophotographic method is placed on the paper. In the image forming apparatus for transferring and outputting to the pre-transfer paper guide displacement means (pre-transfer) for selectively displacing the pre-transfer paper guide 24 to a position close to the photoconductor drum 32 and a position away from the photoconductor drum 32. Guide section (Displacement means) 25 and a position where the pre-transfer paper guide 24 is separated from the photoconductive drum 32 when an image is being formed on the surface of the photoconductive drum 32 in the image forming unit 30a and the paper is not conveyed to the pre-transfer paper guide 24. The drive of the pre-transfer sheet guide displacing means 25 is controlled so as to be displaced in the distance.

First, the overall configuration of the image forming apparatus 1 according to the present embodiment will be described with reference to the drawings. The image forming apparatus 1 has a copy mode, a printer mode, and a FAX mode as print modes. A print mode corresponding to the operation input in step S1 and reception of a print job from an external host device such as a personal computer is selected by a control unit (not shown), and image output corresponding to the print mode is performed.

  As shown in FIG. 1, the configuration of the image forming apparatus 1 is roughly divided into a document reading unit (scanner unit) 10, a paper feeding unit 20, a transfer unit 30, and a paper discharge unit 40, and the document reading unit 10 is a paper feeding unit. The paper discharge unit 40 is disposed above the document reading unit 10 and the paper supply unit 20.

  A platen glass 11 made of transparent glass on which a reading document is placed is provided on the upper surface of the apparatus main body 1a of the image forming apparatus 1. Above the platen glass 11, an ADF (automatic document feeder) 10a is provided. On the other hand, below the platen glass 11, a document reading unit 10 for reading image information of the document is disposed. A transfer unit 30, a fixing device 38, and a paper discharge unit 40 are formed below the document reading unit 10, and further, a paper feed cassette 21 that stores a recording medium is disposed below the document reading unit 10. Yes.

  The image reading unit 10 is disposed below the platen glass 11 and reciprocally moves in parallel. The copy lamp unit 12 and the second scanning unit 13 which are first scanning units, an optical lens 15, and a CCD (photoelectric conversion element). ) 16. The optical path of the image reading unit 10 is indicated by a one-dot chain line.

  The copy lamp unit 12 has a copy lamp 12a, a reflector 12c that exposes the light from the copy lamp 12a on the surface of the original image, and a reflected light image from the original that is exposed and reflected through the reflector 12c in a predetermined direction. And a first mirror 12b for guiding the head toward the bottom, and the reciprocating movement is controlled in parallel at a predetermined scanning speed while maintaining a certain distance from the lower surface of the platen glass 11.

  The second scanning unit 13 has a second mirror 13a and a third mirror 14 for guiding the reflected light image from the document guided by the first mirror 12b of the copy lamp unit 12 further in a predetermined direction. The reciprocating movement is controlled in parallel with the copy lamp unit 12 while maintaining a constant speed relationship.

  The optical lens 15 is disposed on the optical path of the reflected light of the original image guided by the third mirror 14 of the second scanning unit 13 and forms the optical image on the CCD 16.

  The CCD 16 reads a light image of a document image formed by the optical lens 15 and photoelectrically converts it into an electrical signal to create document image information (document image data). The document image information is an image to be described later. It outputs toward the process part 52 (refer FIG. 3).

  The image processing unit 52 performs image processing on the document image information output from the CCD 16 into printing image information (printing image data) whose resolution, density, and the like are suitable for printing. The image information for printing after image processing is transferred to an image data input unit of an LSU (laser scanning unit) 33.

  The LSU 33 irradiates the surface of the photosensitive drum 32 constituting the image forming unit 30a with laser light corresponding to the printing image information output from the image processing unit 52. Thereby, an electrostatic latent image of image information for printing is written and formed on the photosensitive drum 32.

  The transfer unit 30 mainly includes an image forming unit 30a that forms a toner image on the surface of the photosensitive drum 32, and a transfer unit (for example, a corona charger) that transfers the toner image formed on the surface of the photosensitive drum 32 to a sheet. ) 36.

  The image forming unit 30a mainly includes a photosensitive drum 32, an LSU 33, a main charging unit 34, a developing device 35, and the like. A cleaner unit 37 for cleaning residual toner remaining on the photosensitive drum 32 after being transferred by the transfer unit 36 is disposed on the outer peripheral portion of the photosensitive drum 32.

  The LSU 33 irradiates a laser beam for forming an electrostatic latent image on the surface of the photosensitive drum 32. The main charging unit 34 has a function of a static elimination device (not shown) that charges the surface of the photosensitive drum 32 to a predetermined potential and removes charges on the surface of the photosensitive drum 32 after cleaning by the cleaner unit 37. .

  The developing device 35 includes a developing tank 35a in which toner is stored, an MG roller (developing roller) 35s that supplies toner to the photosensitive drum 32, and a toner hopper 35t that replenishes toner to the developing tank 35a. The electrostatic latent image formed by the laser beam is developed with toner and visualized as a toner image.

  The transfer unit 36 transfers the toner image of the original image visualized by the developing device 35 onto the paper fed from the paper feed cassette 21.

  The fixing device 38 includes a heat roller 38a and a pressure roller 38b, and rotates the heat roller 38a in a state where the sheet is sandwiched between the heat roller 38a and the pressure roller 38b, so that the heat roller 38a and the pressure roller 38b are in contact with each other. By passing the toner, the toner image transferred onto the paper is melted and fixed on the paper.

  The paper discharge unit 40 mainly includes a paper discharge roller 41 and a paper discharge tray 42.

  Further, on the inner bottom side of the apparatus main body 1a of the image forming apparatus 1, a replaceable sheet cassette 21 in which sheets are stacked and accommodated for each predetermined sheet size is disposed. A half-moon-shaped paper feed roller (also referred to as “pickup roller”) 22 is disposed on the paper discharge side of the paper feed cassette 21.

  The paper feed roller 22 picks up the sheets stacked and accommodated in the paper feed cassette 21 one by one from the uppermost layer, and toward the downstream side (for convenience, the paper flow-out side (cassette side) is upstream and the paper discharge side is It is conveyed to a registration roller (also referred to as “idle roller”) 31 (which is downstream).

  A PIN sensor (recording medium detecting means) 23 is provided on the upstream side of the registration roller 31. The PIN sensor 23 detects a sheet fed and conveyed from the sheet cassette 21. The sheet is fed to the transfer unit 30 while feeding timing based on the detection signal.

  An ADF (automatic document feeder) 10a has a document tray Xa on which documents are placed. When a plurality of documents are read continuously, the document placed on the document tray Xa is picked up by a document. The document is fed by the roller 17a, and the document is introduced into the apparatus via the document feeding roller 17b and guided and conveyed upstream of the registration roller (PS roller) 17c.

  The document transported to the registration roller 17c is transported onto a document reading table 11a made of slit glass arranged adjacent to one side of the platen glass 11, and scanned by the copy lamp unit 12 as the document moves. Then, the document whose image reading has been completed on the document reading table 11a is transported to the document discharge roller 17e via the transport roller 17d and discharged onto the document discharge tray 18.

Here, a copy mode among the print modes in the image forming apparatus 1 will be described.
As shown in FIG. 1, after placing a document on the platen glass 11 of the document reading unit 10 of the image forming apparatus 1, the sheet feeding cassette 21 of the sheet feeding unit 20 or an optional sheet feeding tray Xb provided on the side surface of the apparatus. In addition, after entering the printing conditions with the condition input keys (number of prints / printing magnification, etc.) on the operation panel (not shown) located on the exterior front of the device, press the start key on the operation panel. The copy operation is started by the operation.

  When the start key is operated, a main drive motor (not shown) is started and each drive gear rotates. Thereafter, the paper feed roller 22 on the paper feed cassette 21 side or the paper feed roller 22 a on the optional paper feed tray Xb side rotates to feed the paper into the apparatus, and the fed paper reaches the registration roller 31. The presence or absence of a sheet fed upstream of the registration roller 31 in the sheet conveyance direction is detected by the PIN sensor 23.

  The paper transported to the registration roller 31 is temporarily stopped to synchronize with the leading edge of the image formed on the photosensitive drum 32 (image formation start part), and the leading edge of the paper is uniformly applied to the registration roller 31. The leading edge of the paper is corrected by being pressed.

  On the other hand, in the document reading section 10, the copy lamp 12a is turned on, and the exposure starts when the copy lamp unit 12 moves in the arrow A direction. Irradiation light applied to the original by the copy lamp 12a becomes reflected light (reflected light from the original) including image information of the original, and the reflected light is transmitted from the first mirror 12b provided in the copy lamp unit 12 to the second light. Input from the mirror 13a, the third mirror 14, and the optical lens 15 to the CCD 16 and read.

  The image information read in this way is converted into an electrical signal by a CCD circuit included in a control unit (not shown), and the image information signal is subjected to image processing under a set condition. And sent to the LSU 33 as print data.

  On the other hand, the entire photosensitive drum 32 is charged to a predetermined charging potential by the main charging unit 34. Laser light from the LSU 33 is applied to the photosensitive drum 32 through a polygon mirror (not shown) and various lenses, and an electrostatic latent image is formed on the photosensitive drum 32. Thereafter, the toner on the MG roller 35s in the developing tank 35a is attracted onto the surface of the photosensitive drum 32, and the electrostatic latent image is visualized by the toner according to the potential gap on the photosensitive drum 32. The toner is stored in the toner hopper 35t and supplied to the developing tank 35a.

  Further, the sheet on which the toner image is transferred is conveyed by the registration roller 31 in time, guided by the pre-transfer sheet guide 24 and conveyed to the photosensitive drum 32. Then, the toner on the photosensitive drum 32 is transferred to the paper by the transfer unit 36. At this time, the toner remaining on the photosensitive drum 32 without being transferred onto the paper is scraped off and collected by the cleaning blade of the cleaner unit 37.

  On the other hand, the paper on which the toner image has been transferred is subjected to heat and pressure by passing through the pressure contact portion between the heat roller 38a and the pressure roller 38b of the fixing device 38 in the fixing process, and unfixed toner on the paper is removed. The sheet is melted and fixed to the sheet, and is discharged to the sheet discharge tray 42 by the sheet discharge roller 41.

  In addition, when a predetermined sensor (not shown) detects that a document is placed on the document tray Xa of the ADF 10a included in the document reading unit 10, the document is automatically supplied continuously by the ADF 10a and a copy is made. Executed.

  That is, when the start key operation is performed, the document feeding roller 17b of the ADF 10a rotates, and the document placed on the document tray Xa is sent into the document reading unit 10 and conveyed by a predetermined conveyance path 17f. On the other hand, the document being conveyed is exposed while the copy lamp unit 12 is stopped at a predetermined stop position. The document whose image has been read in this manner is discharged to the document discharge tray 18.

Next, characteristic pre-transfer paper guides 24 and pre-transfer paper guide displacement means 25 according to the present embodiment will be described with reference to the drawings.
FIG. 2A is a front view showing the configuration of the pre-transfer paper guide and the pre-transfer paper guide displacing means constituting the image forming apparatus according to the present embodiment, and FIG. 2B is a view taken in the direction of arrow B in FIG.

  In the image forming apparatus 1, as shown in FIGS. 2A and 2B, the pre-transfer sheet guide 24 disposed in the vicinity of the photoconductive drum 32 is positioned near the photoconductive drum 32 and the photoconductive drum 32. Pre-transfer sheet guide displacement means 25 for selectively displacing to a separated position is provided.

  As shown in FIGS. 1, 2A, and 2B, the pre-transfer paper guide 24 has a guide portion 24a that guides the paper toward the photosensitive drum 32, and a support that rotatably supports the guide portion 24a. The shaft 24b and the arm portion 24c connected to the pre-transfer paper guide displacement means 25 are integrally provided.

  As shown in FIGS. 2A and 2B, the guide portion 24 a is formed in a long rectangular shape along the axial direction of the photosensitive drum 32, and one end portion 24 a 1 along the axial direction of the photosensitive drum 32 is formed. A support shaft 24b is integrally provided at the other end 24a2 so as to face and face the photosensitive drum 32.

  The support shaft 24b is a long shaft body along the axial direction of the photosensitive drum 32, and both ends of the support shaft 24b are rotatably attached to the apparatus side (not shown). An arm portion 24c protrudes from one end side of the support shaft 24b in the axial direction.

  One end of the arm portion 24 c is integrally connected to the support shaft 24 b, and the other end is connected to a part of the pre-transfer paper guide displacement means 25, and interlocks with the operation of the pre-transfer paper guide displacement means 25. Thus, the support shaft 24b is rotated as a fulcrum.

  As shown in FIG. 2B, the pre-transfer paper guide displacement means 25 mainly includes a pre-transfer paper guide solenoid (hereinafter referred to as “solenoid”) 25a and a spring member (tensile coil spring) 25c. It is configured.

  The solenoid 25a is configured such that the plunger 25b appears and disappears when the power is turned ON / OFF. The other end portion of the arm portion 24c is connected to the distal end portion of the plunger 25b, and the spring member 25c is connected. The spring member 25c is provided so as to bias the plunger 25b in a protruding direction.

  In the present embodiment, as shown in FIG. 2B, the solenoid 25a draws the plunger 25b toward the main body 25a1 when energized (ON state). At this time, the arm portion 24c rotates clockwise in the drawing in conjunction with the operation of the plunger 25b, and the pre-transfer sheet guide 24 is displaced to a position where the guide portion 24a is separated from the photosensitive drum 32. (The two-dot chain line portion of the guide portion 24a). The position of the pre-transfer paper guide 24 at this time is set so that the distance between the pre-transfer paper guide 24 and the photosensitive drum is 1.5 mm or more.

  On the other hand, when the energization of the solenoid 25a is released (OFF state), the plunger 25b protrudes outside the main body 25a1 by the spring member 25c. At this time, in the pre-transfer paper guide 24, the arm portion 24c rotates counterclockwise in the drawing in conjunction with the operation of the plunger 25b, and the guide portion 24a is displaced to a position close to the photosensitive drum 32. (The two-dot chain line portion of the guide portion 24a).

  Further, a pre-transfer sheet guide positioning pin (pre-transfer guide member regulating member) 26 for regulating the distance between the guide unit 24a and the photoconductive drum 32 is provided between the photoconductive drum 32 and the guide unit 24a. .

  The pre-transfer paper guide positioning pin 26 contacts when the pre-transfer paper guide 24 comes close to the photoconductive drum so that the distance between the pre-transfer paper guide 24 and the photoconductive drum is 0.6 to 1.0 mm. Has been placed.

  Next, overall electrical control of the image forming apparatus 1 according to the embodiment will be described based on a block diagram. FIG. 3 is a block diagram illustrating a part of the configuration of the control unit of the image forming apparatus according to the present embodiment.

  As shown in FIG. 3, the image forming apparatus 1 performs document image reading processing, image processing, image forming processing, and the like by a main control unit 50 constituting a control unit.

  In the image forming apparatus 1, original image information (original image data) read by the original reading unit 10 or original image information transmitted from each terminal device connected to a communication network is transmitted by the communication unit 51 to the image processing unit. 52 is input.

  The communication unit 51 is an interface for connecting to an external PC or a FAX line.

  The image processing unit 52 processes document image information stored in an image memory 53 such as a RAM into a print image suitable for printing (image formation on paper) by the above program. The image information for printing is input to the image forming unit 30a.

  Further, the image forming apparatus 1 synchronizes the driving actuators such as the document reading unit 10, the image forming unit 30a, the fixing device 38, and the paper discharge unit 40 according to the set operating conditions, as shown in FIG. Let me control it.

  The drive motors of these drive units can be appropriately configured through a power transmission mechanism using the same or different motors as drive sources.

Next, electrical control of the transfer unit 30 will be described based on a block diagram.
FIG. 4 is a block diagram illustrating a part of the configuration of the control unit of the transfer unit constituting the image forming apparatus according to the present embodiment.

  As shown in FIG. 4, the image forming apparatus 1 is provided with a sub-control unit 60 as a control unit, and the sub-control unit 60 controls driving of each driving unit in the transfer unit 30.

  The sub-control unit 60 is connected to the drive motor 61, the registration roller clutch 62, the solenoid 25a, and the paper feed roller clutch 63, and performs drive control via the drivers 61a, 62a, 25a2, and 63a, and the PIN sensor 23 and LSU 33. It is connected to the.

  The drive motor 61 drives all the mechanisms of the apparatus. The registration roller clutch 62 drives / stops the rotation of the registration roller 31. The solenoid 25 a moves the pre-transfer sheet guide 24 away from and in contact with the photosensitive drum 32. The PIN sensor 23 is disposed upstream of the registration rollers 31 in the paper conveyance direction, and detects the presence or absence of paper. The paper feed roller clutch 63 controls the operation of feeding the paper from the paper feed cassette 21 by rotating the paper feed roller 22 for a predetermined time.

  The sub-control unit 60 separates the pre-transfer paper guide 24 from the photoconductive drum 32 when an image is being formed on the surface of the photoconductive drum 32 in the image forming unit 30a and the paper is not conveyed to the pre-transfer paper guide 24. The drive of the solenoid 25a is controlled so as to be displaced to the position.

Here, the drive control of the pre-transfer paper guide displacement means 25 by the sub-control unit 60 and the operation of the pre-transfer paper guide 24 by the pre-transfer paper guide displacement means 25 will be described with reference to timing charts and drawings.
FIG. 5 is a timing chart showing an example of drive control by the sub control unit in the image forming unit of the image forming apparatus according to the present embodiment.

  In the image forming apparatus 1, when a printing process is performed, when the paper feed roller clutch 63 is energized (ON state), the drive is transmitted to the paper feed roller 22, and the paper feed roller 22 rotates to feed the paper feed cassette. One sheet is fed out from 21. The paper conveyed from the paper feed cassette 21 to the registration roller 31 is detected by the PIN sensor 23.

  As shown in FIG. 5, an image writing timing signal is output to the LSU 33 after t1 + t7 (time) from the time T1 when the PIN sensor 23 is detected when the paper conveyed by the paper feed roller 22 is detected by the PIN sensor 23. The LSU 33 irradiates the photosensitive drum 32 with an image writing laser. t7 corresponds to a standby time when the fixing warm-up is not completed.

  At t2 (time) after the image writing timing signal is turned on, the registration roller clutch 62 is turned on and the sheet is fed out toward the photosensitive drum 32.

  At this time, as shown in FIG. 2B, the pre-transfer sheet guide 24 is in a state where the arm portion 24c is pulled by the spring member 25c, so that the guide portion 24a is close to the photosensitive drum 32. It has become.

  Then, as shown in FIG. 5, at time t5 after the registration roller clutch 62 is turned on, the paper feed roller clutch 63 is turned on to supply the next sheet, and the printing process is continuously performed.

  In addition, the registration roller clutch 62 is turned off after t4 from the time T2 when the trailing edge of the conveyed paper passes the PIN sensor 23, the solenoid 25a is turned on after t8, and the plunger 25b is pulled to the solenoid body side.

  As a result, the arm portion 24c is displaced to the solenoid 25a side (leftward in the figure), so that the guide portion 24a is separated from the photoconductive drum 32, so that the residual toner discharged from the photoconductive drum 32 is not affected. It is possible to prevent the pre-transfer paper guide 24 from being contaminated when the paper is passed.

  As an example of the present embodiment, in the apparatus in which the diameter of the photosensitive drum 32 is 30 mm and the process speed is 88 mm / sec and 125 mm / sec, the interval between the pre-transfer sheet guide 24 and the photosensitive drum 32 is 0. It has been confirmed by experiments that transferability is good when the thickness is .6 to 1.0 mm, and that the stain is improved when the pre-transfer paper guide 24 is separated from the photosensitive drum 32 by 1.5 mm or more. .

  As described above, according to the present embodiment, the pre-transfer paper guide 24 is provided in the vicinity of the photoconductive drum 32, and the pre-transfer paper guide 24 is located near the photoconductive drum 32 and the photoconductive drum 32. A pre-transfer paper guide displacing means 25 for selectively displacing the pre-transfer paper guide displacing means 25 is provided at a separated position, and driving of the pre-transfer paper guide displacing means 25 is controlled by the sub-control unit 60. By disposing the toner image near the photosensitive drum 32, it is possible to improve the transferability of the toner image. On the other hand, in the image forming unit 30a, an image is being formed on the surface of the photosensitive drum 32 and the paper guide 24 before transfer. When the paper is not conveyed to the front, the pre-transfer paper guide displacing means 25 is driven to displace the pre-transfer paper guide 24 to a position away from the photosensitive drum 32. Runode, the residual toner discharged from the photoreceptor drum 32 that pre-transfer paper guide 24 during the non-sheet passing is contaminated can be prevented. Therefore, according to the present exemplary embodiment, high-quality image output can be realized by improving toner image transferability without causing toner contamination on the paper.

  Further, according to the present embodiment, the solenoid 25a and the spring member 25c are used as the configuration of the pre-transfer paper guide displacing means 25, so that the pre-transfer paper guide 24 can be controlled with a simple configuration and simple control. it can.

  The present invention is not limited to the configuration of the pre-transfer guide member displacing means. For example, the pre-transfer paper guide 24 may be displaced using a drive motor, a link mechanism, a cam mechanism, or the like. .

  In this embodiment, the sub-control unit 60 performs drive control of the image forming unit 30a. However, the present invention is not limited to the configuration of the control unit, and for example, drive control of the apparatus main body. The controller that performs the above-described function may have a function of controlling the driving of the driving member according to the present invention such as the solenoid 25a.

  Furthermore, the present invention is not limited to the configuration and shape of the pre-transfer guide member, and the configuration and shape can be developed in any manner depending on the apparatus configuration.

  The preferred embodiments and examples of the present invention have been described above. However, it goes without saying that the present invention is not limited to the above-described examples, and those skilled in the art will recognize various types within the scope of the claims. It will be apparent that variations and modifications of the present invention can be conceived, and these are naturally understood to fall within the technical scope of the present invention.

1 is an explanatory diagram showing an overall configuration of an image forming apparatus according to an embodiment of the present invention. (A) is a front view which shows the structure of the pre-transfer paper guide and the pre-transfer paper guide displacement means which comprise the said image forming apparatus, (b) is a B arrow view of (a). FIG. 2 is a block diagram illustrating a part of a configuration of a control unit of the image forming apparatus. FIG. 2 is a block diagram illustrating a part of a configuration of a control unit of a transfer unit constituting the image forming apparatus. 3 is a timing chart illustrating an example of drive control by a sub control unit in an image forming unit of the image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 20 Paper feed part 22, 22a Paper feed roller 23 PIN sensor (recording medium detection means)
24 Pre-transfer paper guide (pre-transfer guide member)
24a guide portion 24c arm portion 25 pre-transfer sheet guide displacement means (pre-transfer guide member displacement means)
25a Solenoid 25b Plunger 25c Spring member 26 Pre-transfer paper guide positioning pin (pre-transfer guide member regulating member)
30 Transfer section 30a Image forming section 31 Registration roller 32 Photosensitive drum 33 LSU
50 Main Control Unit 51 Communication Unit 52 Image Processing Unit 53 Image Memory 60 Sub Control Unit (Control Unit)
61 drive motor 62 registration roller clutch 63 paper feed roller clutch

Claims (5)

A photosensitive drum on which an electrostatic latent image is formed and a toner image is formed based on the electrostatic latent image; an image forming unit that forms an electrostatic latent image on the surface of the photosensitive drum; and A transfer portion that transfers the toner image formed on the recording medium to the conveyed recording medium, and a pre-transfer guide member that is disposed at a predetermined interval with respect to the surface of the photosensitive drum and guides the recording medium to the transfer portion. In an image forming apparatus for transferring and outputting a toner image formed on the surface of the photosensitive drum by electrophotography on a recording medium,
A pre-transfer guide member displacing means for selectively displacing the pre-transfer guide member to a position close to the photoconductive drum and a position spaced from the photoconductive drum;
A controller for controlling the driving of the pre-transfer guide member displacing means,
The controller is configured to position the pre-transfer guide member away from the photoconductive drum when an image is formed on the surface of the photoconductive drum at least in the image forming unit and the recording medium is not conveyed to the pre-transfer guide member. An image forming apparatus, wherein the drive of the pre-transfer guide member displacing means is controlled so as to be displaced to the right.   2. The control unit according to claim 1, wherein the pre-transfer guide member displacing unit causes the pre-transfer guide member displacing unit to displace the pre-transfer guide member to a position separated from the photosensitive drum by energizing the pre-transfer guide member displacing unit. The image forming apparatus according to 1.   The pre-transfer guide member regulating member that regulates an interval between the pre-transfer guide member and the photoconductive drum when the pre-transfer guide member is displaced to a position close to the photoconductive drum. The image forming apparatus according to 1 or 2.   The pre-transfer guide member has a distance between the pre-transfer guide member and the photosensitive drum of 0.6 to 1.0 mm at a position close to the photosensitive drum, and 1.5 mm at a position apart from the photosensitive drum. The image forming apparatus according to claim 1, wherein the image forming apparatus is set so as to satisfy the above. A recording medium detection means for detecting a recording medium conveyed to the pre-transfer guide member on a recording medium conveyance path upstream of the pre-transfer guide member in the recording medium conveyance direction;
The recording medium detection means detects an upstream end of the recording medium to be conveyed in the recording medium conveyance direction,
The control unit is configured to displace the pre-transfer guide member to a position separated from the photosensitive drum based on the passage timing of the upstream end of the recording medium in the recording medium conveyance direction detected by the recording medium detection unit. The image forming apparatus according to claim 1, wherein the driving of the pre-transfer guide member displacing unit is controlled.

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