JP4574557B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic system, and more particularly to an image forming apparatus provided with a peeling member for peeling a sheet from a photosensitive drum.

  In an image forming apparatus using an electrophotographic system, when image information is transferred to a conveyed sheet, a toner image visualized on the peripheral surface of the photosensitive drum is transferred using a transfer electric field. It is common. At this time, since the surface potential on the photosensitive drum is larger than the transfer electric field and acts on the conveyance sheet in the white background portion (portion where the toner image is not transferred) of the conveyance sheet, the sheet is attracted to the photoreceptor.

  In general, a white background portion where a toner image is not transferred is often disposed in the leading edge region of the paper, and this region is called a “void region”. The void area is formed by the melted toner when the toner image transferred by the thermal fixing device is melted and fixed (fixed) to the paper after the transfer process is completed and the toner image is transferred to the paper. It has a role of preventing the leading end of the sheet from being caught and causing the jamming.

  However, since the void area is easily attracted to the photosensitive drum as described above, a peeling claw for returning the attracted paper to the paper transport path is often provided. If the peeling claw is not provided, the adsorbed paper is not peeled from the photosensitive drum, and is transported with the photosensitive drum adhering to the peripheral surface of the photosensitive drum, and a cleaning unit or main unit disposed around the photosensitive drum. It may reach the charger, developing tank, etc. If this occurs, the surface of the photoreceptor is damaged, leading to a reduction in printing quality and a reduction in the life of each unit. In the worst case, the apparatus is destroyed.

  A conventional image forming apparatus provided with a peeling claw will be described with reference to FIG. FIG. 6 is a side view showing a partial configuration of a conventional image forming apparatus 101.

  As shown in FIG. 6, a registration roller 111, a paper guide 112, a transfer charger 113, a paper peeling charger 114, a paper guide 115, a paper peeling portion 120, a cleaning unit 116, and the like are provided around the photosensitive drum 110. ing.

  When the conveyed sheet reaches the registration roller 111, the conveyance is temporarily stopped, and then the conveyance is resumed based on the timing of writing the electrostatic latent image on the photosensitive drum 110. The sheet whose conveyance has been resumed is guided by the paper guide 112 and reaches the contact portion P1 between the photosensitive drum 110 and the transfer charger 113.

  The sheet that has reached P1 is attracted to the peripheral surface of the photosensitive drum 110 on which the electrostatic latent image is actualized and the toner image is formed, and the peripheral surface of the photosensitive drum 110 is generated by the transfer electric field generated by the transfer charger 113. The toner image formed thereon is transferred onto the paper. In general, a DC voltage having any polarity is used to generate the transfer electric field.

  After the toner image is transferred from the photosensitive drum 110 to the paper by the transfer charger 113, the charge of the paper is reduced by the peeling electric field generated by the paper peeling charger 114. As this peeling electric field, a DC voltage superposed with an AC voltage is usually used.

  Although the above-described peeling electric field reduces the adsorption force of the sheet to the photosensitive drum 110, the sheet may not naturally peel from the photosensitive drum 110 when the sheet is weak or has a lot of white background. is there. In such a case, the leading edge of the paper reaches the contact portion P <b> 2 between the paper peeling unit 120 and the photosensitive drum 110 and is forcibly peeled off by the paper peeling member 120.

  FIG. 7 is an enlarged side view showing the detailed structure of the sheet peeling member 120. The sheet peeling unit 120 mainly includes a star roller 120a and a peeling claw 120b. One end of the peeling claw 120b is pressed against the photosensitive drum 110 by a biasing member or the like (not shown), and a star roller 120a is rotatably attached to the other end.

  As shown in FIG. 7A, the peeling claw 120b is provided such that its tip comes into contact with the photosensitive drum. An inclined surface X for guiding the peeled paper is provided in the vicinity of the tip of the peeling claw 120b. As shown in FIG. 7B, the inclined surface X is provided at an angle such that the protrusion provided on the star roller 120a contacts the extended surface.

  In addition, a minute end surface including a normal to the peripheral surface of the contact portion of the photosensitive drum 110 is provided at the tip of the peeling claw 120b that contacts the photosensitive drum 110. That is, the end surface provided at the tip of the peeling claw 120 b is a surface that is substantially perpendicular to the peripheral surface of the photosensitive drum 110.

  A process in which the sheet is peeled by the sheet peeling unit 120 will be described with reference to FIG. FIG. 8 is a diagram showing each stage in which the paper adsorbed on the photosensitive drum 110 is peeled off by the paper peeling unit 120.

  As shown in FIG. 8A, when the leading edge of the paper adsorbed on the photosensitive drum 110 reaches the leading edge of the peeling claw 120b, the leading edge of the paper collides with the end surface provided at the leading edge of the peeling claw 120b. As a result, as shown in FIG. 8B, the leading end region of the paper is buckled.

  When the sheet is further conveyed in this state, the leading end of the sheet is peeled off from the photosensitive drum 110. At this time, the portion immediately behind the leading edge of the sheet is adsorbed to the photosensitive drum 110 and the leading edge region is also in close contact with the peeling claw 120b. As shown to c), it is conveyed along the inclined surface X provided in the peeling nail | claw 120b.

  Since the inclined surface X is inclined so that the downstream side in the sheet conveyance direction is higher than the upstream side, the sheet is opposite to the paper guide 115 provided at the lower part of the photosensitive drum 110 (that is, from the horizontal direction). Is also directed upwards).

  Then, the leading edge of the paper guided along the inclined surface X reaches the protrusion of the star roller 120a as shown in FIG. Then, when the sheet comes into contact with the star roller 120a, the charge accumulated in the sheet by the transfer electric field (the adsorption electric field with the photosensitive drum 110 received in the transfer process) is removed, and the sheet is peeled off. At the same time, the star roller 120a starts to rotate as its protrusion is pushed against the leading edge of the paper. As a result, a flow is generated in the air layer between the paper and the star roller 120a, and the paper peeling from the paper peeling unit 120 is promoted.

  Then, as shown in FIG. 8E, the sheet falls from the leading end side toward the lower paper guide 115 while being bent by its own weight. The paper dropped on the paper guide 115 is then transported toward the subsequent member.

  As described above, the paper adsorbed on the photosensitive drum 110 is reliably peeled off by the paper peeling unit 120, and is prevented from being wound and conveyed to the cleaner blade 116a of the cleaning unit 116.

  When the above-described conventional image forming apparatus is downsized, the sheet peeling charger 114 may be omitted due to problems such as installation space. Also, the sheet peeling charger 114 may be omitted when saving power in the image forming apparatus. In these cases, the role of the sheet peeling unit 120 becomes even more important.

  In such a conventional image forming apparatus, the transfer charger 113 is normally provided at the lower part of the photosensitive drum 110 as shown in FIG. 6, and from there, the sheet peeling unit 120, A cleaning unit 116 is provided. The cleaning unit 116 is for recovering “residual toner” remaining on the peripheral surface of the photosensitive drum 110 after transfer. From the viewpoint of cleaning efficiency, the cleaning unit 116 rotates 90 ° from the lower end of the photosensitive drum 110 in the rotational direction. Provided at the rotated position. The sheet peeling unit 120 is arranged such that an angle α formed between the point P1 where the transfer is performed and the point P2 where the sheet is peeled is in a range of 45 ° ± 10 °.

  From the viewpoint of reducing the pressure contact force of the peeling claw 120b to the photosensitive drum 110, it is preferable that the angle α is close to 90 °. Since the cleaning unit 116 is provided at the rotated position as described above, the angle α cannot be set to 90 °.

  If the angle α is too close to 90 °, a large “wrinkle” is generated on the peeled paper, and the image after transfer is disturbed due to sliding with the photosensitive member or contact with the peeling claw. There is a fear. In addition, if the paper peeling unit 120 is too close to the cleaning unit 116, the paper being peeled may come into contact with the cleaning unit 116, and the paper may become dirty.

  On the other hand, if the angle α is reduced, that is, if the sheet peeling portion 120 is too close to the transfer point P1, the effect of the transfer electric field is generated on the sheet peeling portion 120. The toner image transferred onto the paper may be disturbed, leading to a reduction in image quality. For these reasons, the arrangement position of the sheet peeling unit 120 is set in the above-described range.

  By the way, since the tip of the peeling claw 120b of the paper peeling unit 120 is in contact with the circumferential surface of the photosensitive drum 110, the circumferential surface of the photosensitive drum 110 may be damaged as the rotational time of the photosensitive drum elapses. . Since the peripheral surface of the photosensitive drum 110 is a surface on which a toner image is formed, the quality of an image to be formed is deteriorated when a scratch is generated.

  Therefore, when the paper peeling unit 120 is provided so as to be detachable and the paper does not need to be peeled off, the paper peeling unit 120 is separated from the photosensitive drum 110 and only when the paper passes through the photosensitive drum 110, Patent Documents 1 and 2 propose an image forming apparatus configured to bring the sheet peeling unit 120 into contact with the photosensitive drum 110.

  In Patent Document 1, a clutch mechanism of a control roller that determines a sheet conveyance timing and a separation claw clutch mechanism that performs a separation claw separation operation are arranged coaxially, and both clutch mechanisms are connected and disconnected by the same solenoid. Thus, there has been proposed an image forming apparatus in which the separation / contact operation of the peeling claw is synchronized with the rotation of the control roller.

Further, Patent Document 2 proposes an image forming apparatus that performs a separation claw separation operation with respect to a photosensitive body in accordance with the rotation of the photosensitive member, the presence / absence of a conveyance sheet, and the timing at which the leading end of the sheet reaches the separation claw. Yes.
JP-A-6-27753 (published on February 4, 1994) JP 2002-108110 A (published April 10, 2002)

  However, the above-described conventional image forming apparatus has a problem that jamming and image deterioration are likely to occur when performing high-speed printing processing. Specifically, the conventional image forming apparatus can cope with the number of processed sheets of 60 sheets / minute or less, but when the number of processed sheets is larger than that, particularly when the number of processed sheets is 100 sheets / minute or more. , It has a problem that jam and image deterioration are likely to occur.

  For example, in the case of high-speed printing processing in which the number of sheets to be printed is 120 sheets / minute and the sheet conveyance speed (process speed) is 600 mm / second, the sheet interval is set to a short interval of about 15 to 25 mm. When the sheet interval is short as described above, when the sheet is displaced, the front and rear end portions of the sheet overlap with each other, which may cause image degradation due to occurrence of a jam or rubbing of the printing surface.

  When the toner image is transferred onto the paper, the paper conveyed from the registration roller 111 is subjected to the transfer process in a state where the paper is slightly bent in the transfer region P1. Here, there is no problem if the paper is smoothly peeled at the peeling portion P2, but in some cases, a delay occurs in the peeling timing.

  As a cause of the delay of the peeling timing, firstly, unevenness in the conveyance speed of the paper can be mentioned. Since the adsorption force between the sheet and the photosensitive drum 110 due to the transfer electric field increases and decreases depending on the type of the sheet, the conveyance speed of the sheet on the peripheral surface of the photosensitive drum 110 changes. As a result, a delay occurs in the time for the sheet to reach the sheet peeling unit 120, and a delay in the peeling timing is caused. Usually, the magnitude of the transfer electric field is set with reference to plain paper, and therefore, there is a tendency that the peeling timing is delayed particularly when the paper is thin paper (secondary base paper, etc.), thick paper (postcard, envelope, etc.), etc. .

  Another cause is the winding of the paper around the paper peeling unit 120. For example, when high-speed printing is performed at a process speed of 500 mm / second or more and a number of printed sheets of 100 sheets / minute or more, the paper passes through the transfer area at a high speed of about 2 sheets / second. Therefore, in order to perform transfer reliably within a short process time, it is necessary to increase the transfer electric field for transferring the toner image from the photosensitive drum 110 to the sheet. However, when the transfer electric field is increased, the electrostatic attractive force between the sheet and the photosensitive drum 110 increases, and the sheet is easily wound around the sheet peeling unit 120 or the sheet peeling unit 120 during the sheet peeling process. As a result, the paper is transported to the cleaning unit 116, and the paper is slightly wound around the paper peeling unit 120, and the peeling timing is delayed by that amount, even if the paper does not jam. It becomes.

  For these reasons, when a delay occurs in the peeling timing, the rear portion of the sheet is shifted to the upstream side in the transport direction on the photosensitive drum 110. This positional deviation becomes more significant as the paper size increases. When the positional deviation occurs in this way, if the paper interval is short as described above, the trailing edge of the paper overlaps with the leading edge of the succeeding paper, which causes image degradation or, in the worst case, jamming. It becomes.

  The present invention has been made in view of the above problems, and an object of the present invention is to realize an image forming apparatus capable of reducing image deterioration and jamming during high-speed processing.

  In order to solve the above problems, an image forming apparatus according to the present invention includes a photosensitive drum on which a toner image is formed on a peripheral surface, and abutting a lower peripheral surface of the photosensitive drum via a sheet. Transfer means for transferring the toner image formed on the photosensitive drum to the sheet, and a peeling member for coming into contact with the peripheral surface of the photosensitive drum and for peeling the sheet on which the toner image has been transferred by the transfer means from the photosensitive drum. In the image forming apparatus, the angle from the center of the contact portion of the transfer unit to the contact portion of the peeling member on the peripheral surface of the photosensitive drum with the rotation axis of the photosensitive drum as the center is 20 ° or more and 35 °. The transfer means includes an endless belt that abuts on the photosensitive drum and a plurality of rollers that bridge the endless belt.

  The image forming apparatus according to the present invention is of an electrophotographic system including a photosensitive drum that rotates about a rotation axis, a transfer unit that contacts the photosensitive drum, and a peeling member. According to the above configuration, the angle from the center of the contact portion (transfer point) of the transfer unit to the contact portion (peeling point) of the peeling member on the peripheral surface of the photosensitive drum is 20 ° or more and less than 35 °. .

  As a result of earnest research, the inventor of the present application has found an installation range of a peeling member that can reduce the occurrence of jam when performing high-speed processing. By setting the arrangement of the peeling member within the above range, the peeling point is shifted downward compared to the conventional case, and the weight of the sheet can be efficiently used as a force for peeling the paper from the photosensitive drum. . Therefore, the sheet can be peeled effectively, and the sheet can be prevented from being wound around the peeling member. As a result, the leading edge of the paper is again adsorbed to the photosensitive drum, and is caught in, for example, a cleaning unit provided on the downstream side in the rotation direction of the photosensitive drum, thereby preventing jamming. .

  Moreover, the delay of peeling timing can be prevented by suppressing the winding to a peeling member and performing a peeling process rapidly. As a result, even if the distance between the front and rear sheets is narrow, it is possible to prevent the end portions of the sheets from overlapping each other, and it is possible to prevent image deterioration and jamming.

  Furthermore, by setting the arrangement of the peeling member within the above range, the peeling point becomes lower than in the conventional case, and the sheet peeled off from the photosensitive drum can be quickly moved to the lower part without being greatly bent as in the conventional case. Land. Therefore, it is possible to reduce the influence of unevenness in the conveyance speed on the peripheral surface of the photosensitive drum.

  As described above, when the distance from the transfer point to the peeling point on the peripheral surface of the photosensitive drum is shortened compared to the conventional case, the area on the peripheral surface of the photosensitive drum where the sheet is attracted to the photosensitive drum is reduced. Therefore, the attractive force is also reduced. As a result, when the leading edge of the sheet collides with the peeling member and buckles, the sheet may be displaced and transfer blur may occur. However, if the belt transfer method is used among the electrostatic transfer methods as described above, a wide nip width can be secured and the frictional force between the photosensitive drum and the sheet can be increased. Can be suppressed.

  As described above, according to the image forming apparatus of the present invention, it is possible to reduce image degradation and jamming when performing high-speed processing.

  In the image forming apparatus, the angle is preferably 30 ° or less. As a result, image degradation and jamming can be further reduced.

  In the image forming apparatus, the angle is preferably 25 ° or more.

  If the peeling point is set too low, the sheet may be jammed between the peeling member and the transfer means after the toner image is transferred, and jamming may occur. it can.

  The endless belt is preferably provided on the endless belt so that the leading edge of the sheet peeled off from the photosensitive drum is landed.

  According to the above configuration, since the leading edge of the sheet partially peeled from the photosensitive drum is conveyed by the endless belt, the separation of the sheet is promoted, and the sheet is promptly conveyed to the subsequent member. Retention can be prevented.

  The transfer unit preferably includes a conductive roller having an elastic force for pressing the contact portion of the endless belt with the photosensitive drum against the photosensitive drum.

  According to the above configuration, since the conductive roller contacts and charges the endless belt, the voltage required to generate the transfer electric field can be lowered and power saving can be achieved compared to the case where corona transfer is performed. Can do. Further, since the conductive roller has elasticity, the nip width can be widened.

  The peeling member preferably has an inclined surface that guides the leading end of the sheet peeled from the photosensitive drum in the direction of the endless belt.

  According to the above configuration, the sheet from which the leading end is peeled is smoothly transported in the direction of the endless belt without causing stagnation and sagging, so that the print quality is improved and jamming during transport can be reduced. .

  Moreover, it is preferable that the said peeling member has an inclined surface which guide | induces the front-end | tip part of the sheet | seat peeled from the photoconductor drum downward rather than the horizontal direction.

  According to the above configuration, it is possible to suppress the sheet from being wound around the peeling member and the sheet from being wound into, for example, a cleaning unit.

  In addition, the image forming apparatus further includes a separation / contact control unit that separates and contacts the peeling member with respect to the photosensitive drum, and the separation / contact control unit includes a transfer unit configured to continuously form a toner image on a plurality of sheets. It is preferable to keep the peeling member in contact with the photosensitive drum during the transfer.

  According to the above configuration, since the peeling member is separated from and in contact with the photosensitive drum, scratches generated on the peripheral surface of the photosensitive drum are reduced as compared with a configuration in which the peeling member is always in contact with the photosensitive drum. be able to.

  The separation member remains in contact with the photosensitive drum when the image forming apparatus continuously forms images on a plurality of sheets by the separation / contact control unit that controls separation / contact of the separation member. . Accordingly, even when the sheet conveyance speed fluctuates due to disturbance, the separation contact timing of the separation member is not delayed, so that the sheet can be reliably separated without causing a jam. Accordingly, it is possible to prevent the jammed sheet from scratching the peripheral surface of the photosensitive drum, and it is possible to prevent the toner from scattering in the image forming apparatus due to the occurrence of the jam. it can.

Alternatively, the image forming apparatus further includes separation / contact control means for bringing a peeling member into contact with or separating from the photosensitive drum, and the separation / contact control means is configured such that the transfer means continuously applies toner to a plurality of sheets. When the image is transferred, the contact and separation of the peeling member for each sheet may be repeated.

  According to the above configuration, since the peeling member is separated from and in contact with the photosensitive drum, scratches generated on the peripheral surface of the photosensitive drum are reduced as compared with a configuration in which the peeling member is always in contact with the photosensitive drum. be able to.

  When the image forming apparatus continuously forms an image on a plurality of sheets by the separation / contact control means for controlling separation / contact of the separation member, the separation member is separated from the photosensitive drum for each sheet. And the separation is repeated. In this way, it is possible to suppress scratches on the peripheral surface of the photosensitive drum by bringing the peeling member into contact with the photosensitive drum only when necessary. As a result, it is possible to stabilize the print quality and extend the life of the photosensitive drum.

  The transfer unit includes an endless belt that contacts the photosensitive drum and also conveys the sheet peeled from the photosensitive drum, and a plurality of rollers that bridge the endless belt. Is the timing at which the peeling member is brought into contact with the photosensitive drum when the leading edge of the sheet reaches the contact portion between the photosensitive drum and the transfer unit, and the leading edge of the sheet peeled off from the photosensitive drum is brought into contact with the endless belt. It is preferable to separate the peeling member from the photosensitive drum.

  Alternatively, the separation / contact control means causes the peeling member to contact the photosensitive drum at a timing when the leading edge of the sheet reaches the contact portion between the photosensitive drum and the transfer means, and the trailing edge of the sheet peels from the photosensitive drum. The peeling member may be separated from the photosensitive drum at the timing when it passes through the contact portion with the member.

  In the image forming apparatus, the diameter of the photosensitive drum is preferably 100 mm or more and 150 mm or less.

  As described above, in the image forming apparatus according to the present invention, the angle from the contact portion of the transfer unit to the contact portion of the peeling member on the peripheral surface of the photosensitive drum, with the rotation axis of the photosensitive drum as the center, is 25. It is the structure which is more than 35 degrees. Therefore, as described above, when high-speed processing is performed, there is an effect that image degradation and occurrence of jam can be reduced.

  An image forming apparatus according to an embodiment of the present invention will be described below with reference to FIGS. FIG. 2 is a cross-sectional view illustrating a schematic configuration of the image forming apparatus 1 according to the present embodiment.

  The image forming apparatus 1 according to the present embodiment forms a monochrome image on a predetermined sheet (recording paper) in accordance with image data transmitted from the outside. As shown in the figure, the exposure unit 2, the developing device 3, the photosensitive drum 10, the transfer unit 13, the charger 4, the cleaning unit 16, the fixing unit 6, the paper transport path 7, the paper feed tray 8, and the paper discharge A tray 9 and a control unit 50 are provided.

  The charger 4 is a charging unit for uniformly charging the peripheral surface of the photosensitive drum 10 to a predetermined potential. As the charger 4, a charger-type charger 4 may be used as shown in FIG. 1, or a contact-type roller-type or brush-type charger may be used.

  The exposure unit 2 performs exposure according to image data input to the photosensitive drum 10 uniformly charged by the charger 4, and an electrostatic latent image corresponding to the image data is applied to the surface of the photosensitive drum 10. To form.

  As the exposure unit 2, as shown in FIG. 1, a laser scanning unit (LSU) provided with a laser irradiation unit 2a and a reflection mirror 2b may be used, or light emitting elements (for example, EL and LED) are arranged in an array. A write head may be used. Note that the image forming apparatus 1 of the present embodiment employs a two-beam technique that reduces the speed of irradiation timing by using a plurality of laser beams in order to perform high-speed printing processing.

  The developing device 3 visualizes the electrostatic latent image formed on the peripheral surface of the photosensitive drum 10 with black toner and forms a toner image.

  The transfer unit 13 transfers the toner image visualized on the photosensitive drum 10 by the developing device 3 to the conveyed paper. Details of the transfer unit will be described later.

  The fixing unit 6 melts the toner image transferred onto the paper by the transfer unit 13 and fixes it on the paper. The fixing unit 6 includes two rollers, a heating roller and a pressure roller.

  A paper peeling claw, a roller surface temperature detection member (thermistor), a cleaning unit for cleaning the roller surface, and the like are disposed on the outer peripheral portion of the heating roller 61. Further, the surface of the heating roller is placed at a predetermined temperature on the inner peripheral portion. A heat source for heating to a fixed fixing temperature (approximately 160 to 200 ° C.) is disposed.

  On the other hand, the pressure roller is provided with a pressure member at both ends of the roller so that the pressure roller can be pressed against the heating roller with a predetermined pressure. A sheet peeling claw, a cleaning unit and the like are arranged in the same manner as the outer periphery of the sheet.

  The fixing unit 6 melts unfixed toner on the conveyed paper at the surface temperature of the heating roller and presses it with two rollers at a pressing portion (hereinafter referred to as “fixing nip portion”) between the heating roller and the pressure roller. To fix on the paper.

  The cleaning unit 16 removes and collects toner remaining on the surface of the photosensitive drum 10 after development and image transfer.

  The paper feed tray 8 is a tray for storing sheets (paper) used for image formation. In the present embodiment, in order to perform high-speed printing processing on a large amount of paper, a plurality of paper feed trays 8 and 8 are arranged in the lower portion of the image forming apparatus 1, and each tray has 500 to 500 standard-size paper. 1500 sheets are stored. In addition to the paper feed tray 8, printing is performed on the side portion of the image forming apparatus 1 on a large-capacity paper feed cassette 81 capable of storing a large amount of a plurality of paper types, and mainly on irregular-size paper. A manual feed tray 82 used at the time is further arranged.

  The paper discharge tray 9 holds paper on which image formation has been completed. The paper discharge tray 9 is disposed on the side of the image forming apparatus 1 opposite to the manual feed tray 82. In addition, the image forming apparatus 1 according to the present embodiment has an optional post-processing apparatus that performs stapling and punching on the paper after image formation, and a multi-stage paper discharge tray, as an option, instead of the paper discharge tray 9. It is also possible to arrange.

  The control unit 50 is for performing operation control on the above-described units and image processing on image data. The control unit 50 is a microcomputer including at least a CPU and a RAM, and functions by reading a program recorded on a recording medium (not shown).

  Next, a paper conveyance process of the image forming apparatus 1 will be described.

  When a print request is transmitted from the outside of the image forming apparatus 1, a sheet that matches the print request is selected from the plurality of paper feed trays 8 and conveyed to the registration rollers by the conveyance rollers. The paper that has reached the registration roller is temporarily stopped and conveyed again at the timing when the leading edge of the paper and the leading edge of the toner image on the photosensitive drum 10 coincide. Then, after the toner image is transferred onto the sheet at the nip portion described above, the toner image is fixed by the fixing unit 6 and discharged to the sheet discharge tray 9.

  Here, when the image forming apparatus 1 has a plurality of modes (for example, a copier mode, a printer mode, and a FAX mode) and a plurality of printing processing methods (for example, single-sided printing and double-sided printing), the sheet is discharged from the fixing unit 6. The conveyance path to the tray 9 changes according to the mode and the printing processing method. Normally, in the copier mode, the “face-up discharge” in which the user performs operations around the apparatus and discharges with the printing surface on the upper side is often used, while in the printer and FAX modes, This is because “face-down discharge” that aligns the page order of discharged sheets is often used because the user is not in the vicinity of the apparatus.

  Accordingly, the image forming apparatus 1 has a plurality of conveyance paths and a plurality of branching claws until the paper that has passed through the fixing unit 6 is discharged to the paper discharge tray 9, and selects the conveyance path according to the purpose. ing.

  In the image forming apparatus 1, a configuration for reducing image degradation and jam that may occur during high-speed printing processing will be described in detail below. FIG. 1 is a side view showing a configuration around the photosensitive drum 10 of the image forming apparatus 1 according to the present embodiment.

  As the photosensitive drum 10, for example, a cylindrical drum having a diameter of about 100 to 150 mm can be used. As shown in FIG. 1, a transfer unit 13, a sheet peeling unit 20, and a cleaning unit 16 are provided around the photosensitive drum 10.

  A transfer unit 13 is provided below the photosensitive drum 10. In the present embodiment, the transfer unit 13 is a belt unit in which an endless belt 13a is bridged with a plurality of rollers 13b to 13e, and is configured to use a belt transfer method among electrostatic transfer methods.

  The endless belt 13 a is in contact with the vertical lower end P <b> 1 of the photosensitive drum 10. Hereinafter, this contact portion is referred to as “transfer nip portion P1”. In the present embodiment, the transfer nip P <b> 1 is formed at the vertically lower end of the photosensitive drum 10 by bringing the endless belt 13 a into contact with the vertically lower end of the photosensitive drum 10. However, the present invention is not limited to this configuration, and the endless belt 13a is brought into contact with the photosensitive drum 10 so that the transfer nip portion P1 is formed at a portion other than the vertical lower end portion of the photosensitive drum 10. Also good.

  As a roller for bridging the endless belt 13a, the transfer unit 13 includes a conductive roller 13b, a driving roller 13c, a driven roller 13d, and a charge eliminating roller 13e. The drive roller 13c is connected to a drive motor (not shown) so that a drive force can be generated in the rotation direction of the roller. The driving roller 13c is rotated by generating a driving force, and the other rollers 13b, 13d, and 13e are driven to rotate, whereby the endless belt 13a is rotated.

  The conductive roller 13b is provided at a position facing the photosensitive drum 10 with the endless belt 13a interposed therebetween so as to press the endless belt 13a against the transfer nip portion P1 of the photosensitive drum 10. Since the conductive roller 13b has elasticity, the endless belt 13a and the photosensitive drum 10 are not in line contact but in surface contact. That is, the transfer nip portion P1 has a predetermined width (hereinafter referred to as “nip width”) in the rotation direction of the photosensitive drum 10.

The conductive roller 13b is charged with a DC voltage and generates a transfer electric field, whereby the endless belt 13a having a resistance of about 1 × 10 ⁹ to 1 × 10 ¹³ Ω · cm can be charged. For example, when the toner image is negatively charged, the voltage applied by the conductive roller 13b is positive. In the transfer unit 13, the conductive roller 13b charges the endless belt 13a with a polarity opposite to the polarity of the toner image, so that the toner image formed on the circumferential surface of the photosensitive drum 10 is directed toward the endless belt 13a. Transfer to existing paper. Further, the endless belt 13a is charged, so that the sheet can be sucked and conveyed.

  As shown in FIG. 1, the endless belt 13 a has a distance from the transfer nip portion P <b> 1 to the neutralization roller 13 e at the downstream end in the paper conveyance direction is larger than the radius of the photosensitive drum 10. Thereby, although the details will be described later, the sheet peeled off by the sheet peeling unit 20 falls onto the endless belt 13a, and is attracted to and transported by the charged endless belt 13a.

  A neutralizing roller 13e is provided at the downstream end of the endless belt 13a in the sheet conveyance direction. The neutralizing roller 13e is for neutralizing the sheet charged by the endless belt 13a and the endless belt 13a, and is grounded by a wiring (not shown). The neutralization roller 13e neutralizes the paper, so that the paper can be smoothly conveyed without being attracted to other members in the subsequent conveyance process. Instead of being grounded, the static eliminating roller 13e may apply a voltage having a polarity opposite to the polarity of the transfer electric field (a negative voltage in the above example) to the endless belt 13a.

  Further, the transfer unit 13 is provided with a cleaning unit (not shown) that removes the toner from the endless belt 13a and removes static electricity. This cleaning unit is also grounded in the same manner as the charge removal roller 13e.

  A cleaning unit 16 is provided at a position of the photosensitive drum 10 rotated 90 ° downstream from the transfer nip portion P1 in the rotation direction. The cleaning unit 16 is for recovering toner remaining on the peripheral surface of the photosensitive drum 10 after the toner image is transferred from the photosensitive drum 10 to the sheet. It has a cleaner blade 16a that abuts. The cleaning unit 16 cleans and collects the toner remaining on the photosensitive drum 10 by wiping the circumferential surface of the photosensitive drum 10 with the cleaner blade 16a.

  A sheet peeling unit 20 is provided between the transfer nip P <b> 1 and the cleaning unit 16 in the outer periphery of the photosensitive drum 10. The image forming apparatus 1 may include only one sheet peeling unit 20, but preferably includes a plurality of (for example, four) sheet peeling units 20 along the axial direction of the photosensitive drum 10. . Since the image forming apparatus 1 includes the plurality of sheet peeling units 20..., The sheet can be reliably peeled off.

  The sheet peeling unit 20 includes a peeling claw 20b whose one end is in contact with the peripheral surface of the photosensitive drum 10, and a star roller 20a provided rotatably at the other end of the peeling claw 20b. Hereinafter, the contact portion between the peeling claw 20b and the photosensitive drum 10 is referred to as a “peeling point P2.”

  Here, as shown in FIG. 1, in the sheet peeling portion 20, the angle γ formed by the center (center) of the transfer nip portion P1 and the peeling point P2 in the rotation direction of the photosensitive drum 10 is 20 ° or more and less than 35 °. It is arranged to become. The angle γ is preferably 30 ° or less. The angle γ is preferably 25 ° or more.

  Next, a detailed configuration of the sheet peeling unit 20 will be described. FIG. 3 is a side view showing a detailed structure of the sheet peeling unit 20. As described above, the sheet peeling portion has the peeling claw 20b that comes into contact with the photosensitive drum 10. The peeling claw 20 b is a substantially trapezoidal plate-like member having a constant thickness, and is arranged so that the trapezoidal surface is perpendicular to the rotation axis of the photosensitive drum 10.

  As shown in FIG. 3A, the long side (hereinafter referred to as “side A”) is the upper side and the short side (hereinafter referred to as “side B”) among the two parallel sides in the trapezoid. It is on the lower side. Further, one side (hereinafter referred to as “side C”) sandwiched between side A and side B has an angle formed by side A and side B of approximately 90 °. A star roller 20a is provided on the side of the peeling claw 20b having the side C. Further, the remaining side D forms an acute angle with side A, while forming an obtuse angle with side B. The inclined surface Y including the side D and extending in the thickness direction functions as a guide unit that guides the sheet peeled from the photosensitive drum 10.

  The apex at which the side A and the side D intersect is in contact with the peripheral surface of the photosensitive drum 10. Hereinafter, the vicinity of this apex is referred to as the tip of the peeling claw 20b. Strictly speaking, the tip end portion of the peeling claw 20b is not formed with an acute tip by the side A and the side D, and the tip is cut off. That is, the tip of the peeling claw 20b has an end surface extending in the thickness direction.

  The end surface provided at the tip of the peeling claw 20b includes the end of the side A on the photosensitive drum 10 side, and is in contact with the peripheral surface of the photosensitive drum 10 on the side extending in the thickness direction.

  In the sheet peeling portion 20, the inclined surface Y (guide portion) provided on the peeling claw 20b is arranged on the upstream side (photosensitive drum 10 side) on the downstream side (photosensitive drum 10 side) as shown in FIG. Higher than the star roller 10 side). As a result, the sheet peeled from the photosensitive drum 10 is guided downward in the horizontal direction. In other words, it can be said that the inclined surface Y (guide portion) guides the leading end portion of the sheet peeled from the photosensitive drum in the direction of the endless belt 13 a provided at the lower portion of the photosensitive drum 10.

  In the image forming apparatus 1 of the present embodiment, the star roller 20a is not in contact with the extended surface of the inclined surface Y (guide portion) of the peeling claw 20b. In the present embodiment, the star roller 20a is provided in the event that the sheet is wound around the peeling claw 20b.

  Next, a process in which the paper is peeled from the photosensitive drum 10 by the paper peeling unit 20 will be described. FIG. 4 is an enlarged view showing each stage in which the paper adsorbed on the photosensitive drum 10 is peeled off by the paper peeling unit 20.

  First, the transported paper is stopped once when it reaches the registration roller 11 shown in FIG. 1, and then the transport is resumed by the registration roller 11 based on the timing of writing the electrostatic latent image on the photosensitive drum 10. Is done. The sheet whose conveyance has been resumed is guided by the paper guide 12, and the leading end reaches the endless belt 13 a of the transfer unit 13. Then, the sheet is conveyed while receiving a transfer electric field by the endless belt 13a, and the toner image is transferred from the photosensitive drum 10 at the transfer nip portion P1.

  Subsequently, as shown in FIG. 4A, when the leading edge of the paper adsorbed on the photosensitive drum 10 reaches the leading edge of the peeling claw 20b, the leading edge of the paper collides with the end surface provided at the leading edge of the peeling claw 120b. To do. As a result, as shown in FIG. 4B, the leading end region of the paper is buckled.

  When the sheet is further conveyed in this state, the leading end of the sheet is peeled off from the photosensitive drum 110. At this time, the sheet does not fall immediately because the rear part is adsorbed to the photosensitive drum 10 and the leading end region is also in close contact with the peeling claw 20b, and as shown in FIG. Then, it is conveyed along the inclined surface Y (guide portion) provided on the peeling claw 20b.

  In the sheet peeling unit 20 of the present embodiment, as described above, the inclined surface Y is provided so that the downstream side in the sheet conveyance direction is lower than the upstream side, and thus the sheet is provided below the photosensitive drum 10. The transfer unit 13 is guided to the endless belt 13a side (that is, downward from the horizontal direction).

  The leading edge of the sheet guided along the inclined surface Y (guide portion) reaches the downstream side of the transfer nip portion P1 of the endless belt 13a as shown in FIG. Then, the front end region of the paper is conveyed by the charged endless belt 13a, and as a result, the paper is peeled off from the paper peeling portion 20 as shown in FIG.

  Thereafter, the sheet is transported to the subsequent member by the endless belt 13a while being separated from the photosensitive drum 10 except for the leading end region.

  As described above, in the image forming apparatus 1 of the present embodiment, the position rotated at an angle of less than 35 ° from the center (center) of the transfer nip portion P1 to the downstream side in the rotation direction of the photosensitive drum on the circumferential surface of the photosensitive drum. By disposing the sheet peeling unit 20 so that the peeling point P2 comes to the position, the problem of the conventional image forming apparatus is solved.

  According to this configuration, the direction of the peeling vector generated by the adsorption force of the photosensitive drum 10 and the weight of the paper is inclined downward compared to the conventional case, and the winding around the peeling claw 20b and the photosensitive drum 10 is suppressed. be able to. That is, since the weight of the paper can be efficiently used as the peeling force for peeling the paper, wrapping around the peeling claw 20b and the photosensitive drum 10 can be suppressed. As a result, it is possible to reduce the wrapping of the paper into the cleaning unit 16 resulting from the wrapping of the paper around the peeling claw 20, suppress the delay of the peeling timing, and overlap the edges between the front and rear papers. The jam that occurs can also be reduced.

  Further, since the peeling point P2 where the peeling from the photosensitive drum is performed is lower than that in the conventional case, the sheet peeled off from the photosensitive drum 10 can be quickly sunk without being greatly bent as in the conventional case. Land on 13a. Therefore, it is possible to reduce the influence of unevenness in the conveyance speed on the peripheral surface of the photosensitive drum 10.

  Further, in the image forming apparatus 1 described above, the sheet peeling unit 20 is arranged so that the angle formed by the center (center) of the transfer nip P1 and the peeling point P2 is 20 ° or more on the peripheral surface of the photosensitive drum. ing.

  If the peeling point P2 is set too low, the effect of the transfer electric field is generated in the paper peeling portion 120, and the toner image transferred onto the paper is disturbed due to the peeling discharge and the influence of the transfer electric field when the paper is peeled, leading to a reduction in image quality. There are things to do. However, according to said structure, this can be suppressed.

  Further, in the image forming apparatus 1 described above, the photosensitive drum 10 serves as the transfer unit 13 that transfers the toner image formed on the photosensitive drum 10 to the paper by contacting the peripheral surface of the photosensitive drum 10 via the paper. And an endless belt 13a that abuts the belt and a plurality of rollers 13b to 13e that bridge the endless belt 13a.

  When the distance from the transfer nip portion P1 to the peeling point P2 on the peripheral surface of the photoconductive drum 10 is shortened as compared with the conventional case, the area on the peripheral surface of the photoconductive drum 10 where the sheet is attracted to the photoconductive drum is reduced. The adsorption power is also reduced. As a result, when the leading edge of the sheet collides with the peeling claw 20b and buckles, the sheet may be displaced and transfer blur may occur. However, if the belt transfer method is used among the electrostatic transfer methods as described above, a wide nip width can be secured and the adsorption force between the photosensitive drum and the paper can be increased. Shake can be suppressed.

  Further, in the image forming apparatus 1 described above, the conductive roller 13b having an elastic force for pressing the contact portion of the endless belt 13a with the photosensitive drum 10 against the photosensitive drum 10 side is provided.

  According to this configuration, since the conductive roller 13b is in contact with the endless belt 13a to be charged, the voltage required to generate the transfer electric field can be reduced compared with the case where corona transfer is performed, thereby saving power. Can be planned. Further, since the conductive roller 13b has an elastic force, the nip width can be widened.

  Further, the above-described image forming apparatus 1 is configured to convey the leading edge of the paper partially peeled from the photosensitive drum 10 by the endless belt 13a.

  According to this configuration, since the leading edge of the paper partially peeled from the photosensitive drum 10 is conveyed by the endless belt 13a, the separation of the paper is promoted, and the paper is quickly conveyed to the subsequent member. Sheet retention can be prevented.

  Further, in the image forming apparatus 1 described above, the peeling claw 20b has an inclined surface Y (guide portion) that guides the leading edge of the paper peeled from the photosensitive drum 10 in the direction of the endless belt 13a.

  According to this configuration, the sheet from which the leading end is peeled is smoothly transported in the direction of the endless belt 13a without the retention of the sheet and the slack of the sheet, so that the print quality is improved and there is no possibility of a jam.

  The inclined surface Y (guide portion) also guides the leading end portion of the sheet peeled from the photosensitive drum 10 downward from the horizontal direction. Accordingly, it is possible to prevent the paper from being wound around the paper peeling unit 20 and being caught in the cleaning unit 16.

  Subsequently, a preferred embodiment of the image forming apparatus 1 will be further described.

  In the image forming apparatus 1 of the present embodiment, the above-described sheet peeling unit 20 is provided so as to be able to be separated from and contacted with the photosensitive drum 10. Hereinafter, a case where the image forming apparatus 1 has four sheet peeling portions 20 along the axial direction of the photosensitive drum 10 will be described. FIG. 5 is a diagram illustrating a separation / contact mechanism of the sheet peeling unit 20.

  As illustrated in FIG. 5, the image forming apparatus 1 includes a holding member 30 along the rotation axis of the photosensitive drum 10. The holding member 30 has a rectangular plate 30a having a predetermined thickness, and four convex portions 30b provided upright on the plate 30a. In the plate 30a, the rotational axis of the photosensitive drum 10 is in the longitudinal direction, and the four convex portions 30b are provided at predetermined intervals along the longitudinal direction of the plate 30a.

  Each of the attachment portions 30b is attached with one sheet peeling portion 20. More specifically, the four peeling claws 20b... Are fixed to the convex portion 30b. Here, the respective sheet peeling portions 20 are arranged in the same posture and shifted along the rotation axis so as to come into contact with the peripheral surface of the photosensitive drum 10 in the already described state. . Accordingly, the fixing portions of the peeling claws 20b and the convex portions 30b are aligned in a straight line, and hereinafter, the shaft that passes through the four fixing portions is referred to as a holding shaft 31. The holding shaft 31 is parallel to the rotation axis of the photosensitive drum 10.

  On the other hand, a driving means using a solenoid (not shown) is provided at the end of the holding member 30. By this driving means, the holding member 30 can be rotated around a rotation axis (not shown) parallel to the rotation axis of the photosensitive drum 10. Of course, a drive means other than the solenoid may be used.

  In the present embodiment, as described above, the rotation shaft of the photosensitive drum 10, the holding shaft 31, and the rotation shaft of the holding member 30 are parallel to each other. By rotating around the moving axis, the contact / separation of the four sheet peeling portions 20 to the photosensitive drum 10 can be switched simultaneously.

  In the image forming apparatus 1 of the present embodiment, the four sheet peeling units 20 are simultaneously separated from each other. However, the present invention is not limited to this, and a solenoid or the like is provided for each sheet peeling unit 20. The driving means may be provided, and the contact / separation of the sheet peeling unit 20 may be switched individually.

  By the way, the control of the separation / separation operation of the sheet peeling unit 20 is performed by the control unit 50 (separation / contact control means) described above. In the present embodiment, the control unit 50 controls the voltage applied to the solenoid described above, whereby the sheet peeling unit 20 is in contact with the photosensitive drum 10 (contact state) and the sheet peeling unit 20 is in contact with the photosensitive drum 10. It is possible to switch between two states: a state where the photosensitive drum 10 is separated (a separated state). In FIG. 5, when each sheet peeling portion 20 is rotated in the direction of arrow a, the contact state is established, and when each sheet peeling portion 20 is rotated in the direction of arrow b, the separation state is established.

  The separation / contact control of the sheet peeling unit 20 by the control unit 50 will be described below.

  The timing of contact of the sheet peeling unit 20 with the photosensitive drum 10 is determined based on the re-conveying timing of the registration roller 11 disposed in the preceding stage of the transfer unit 13. As described above, the registration roller 11 temporarily stops the conveyed paper, and then the timing at which the leading edge of the paper and the leading edge of the toner image on the photosensitive drum 10 coincide at the transfer nip portion P1. To re-carry the paper. The control of the conveyance / stop of the registration roller 11 is performed by the control unit 50.

  Here, the control unit 50 turns on the energization of the solenoid so that the sheet peeling unit 20 is brought into contact with the photosensitive drum 10 after a predetermined time T1 has elapsed after instructing the re-conveyance of the registration roller 11. Or OFF). Here, the predetermined time T1 is a time required for the leading edge of the paper to reach the peeling point P2 after the re-conveyance of the paper by the registration roller 11 is started.

  This time T1 depends on the transport distance from the registration roller 11 to the peeling point P2 and the transport speed between them, but since these values are both known, the control unit 50 obtains them by calculating from time to time. Can do. Alternatively, the time required for the leading edge of the sheet to reach the peeling point P2 after the re-conveyance of the sheet by the registration roller 11 is obtained in advance and stored in a storage unit (not shown). The predetermined time T1 may be acquired by referring to it.

  On the other hand, the separation timing of the sheet peeling unit 20 from the photosensitive drum 10 is also determined based on the re-conveying timing of the registration roller 11 as in the case of contact. That is, the control unit 50 turns off (or turns on) the solenoid so that the sheet peeling unit 20 is separated from the photosensitive drum 10 after a predetermined time T2 has elapsed after instructing the re-conveyance of the registration roller 11. ) Here, the predetermined time T2 is a time required for the leading edge of the paper to land on the endless belt 13a after the re-conveyance of the paper by the registration roller 11, and has a value larger than the time T1. . Since this time T2 also depends on the transport distance from the registration roller 11 to the endless belt 13a and the transport speed between them, it can be obtained by calculation by the control unit 50.

  Of course, the time required for the leading edge of the sheet to land on the endless belt 13a after the re-conveyance of the sheet by the registration roller 11 may be measured by a preliminary experiment or the like and stored in the storage unit. In this case, since the time from when the leading edge of the paper passes the peeling point P2 until it reaches the endless belt also varies depending on the type of paper, the paper is re-conveyed by the registration roller 11 for each paper type. It is preferable to measure and store the time required for the leading edge of the paper from landing on the endless belt 13a in the storage unit. Then, the control unit 50 searches the storage unit for a time T2 corresponding to the paper type information set by the user or the like, and searches for the timing of separation of the paper peeling unit 20 from the photosensitive drum 10. This is determined based on the obtained time T2.

  Then, the control unit 50 switches the separation of the sheet peeling unit 20 for each sheet based on the re-conveying timing of the registration roller 11 and the times T1 and T2.

  According to this configuration, the paper peeling unit 20 contacts the photosensitive drum 10 when the leading edge of the paper reaches the peeling point P2, and is separated from the photosensitive drum 10 when the leading edge of the paper lands on the endless belt 13a. To do. The separation / contact operation of the sheet peeling unit 20 is repeated for each sheet.

  The predetermined time T2 may be a time required for the trailing edge of the sheet to pass the separation point P2 after the re-conveyance of the sheet by the registration roller 11 is started. In this case, the time T2 depends on the distance from the registration roller 11 to the peeling point P2, the conveyance speed therebetween, and the paper size. With respect to the paper size, if a value set by the user or the like is acquired, the time T2 can be obtained by the control unit 50 calculating. Of course, as described above, it goes without saying that the time previously obtained by calculation or measurement may be stored in the storage unit.

  According to this configuration, the paper peeling unit 20 contacts the photosensitive drum 10 when the paper reaches the peeling point P2, and is separated from the photosensitive drum 10 when the rear end of the paper passes the peeling point P2. . The separation / contact of the sheet peeling unit 20 is repeated for each sheet.

  As described above, in the image forming apparatus 1 according to the present embodiment, the sheet peeling unit 20 is provided so as to be able to be separated from and contacted with the photosensitive drum 10, and the control unit 50 separates the sheet for each sheet. The unit 20 is configured to repeatedly contact and separate from the photosensitive drum 10. In this way, it is possible to suppress the occurrence of scratches on the peripheral surface of the photosensitive drum 10 by bringing the sheet peeling portion 20 into contact with the photosensitive drum 10 only when necessary. As a result, it is possible to stabilize the print quality and extend the life of the photosensitive drum.

  Incidentally, the separation / contact operation of the sheet peeling unit 20 may be switched for each print job. This modification will be described below.

  When a print request is made from the outside, the control unit 50 creates print job data in response to the request. The print request is, for example, continuous printing of document data transmitted from an external computer or the like on 50 sheets of paper.

  In this modification, the control unit 50 repeats the contact and separation of the sheet peeling unit 20 for each print job. That is, if the above example is used, the control unit 50 makes the sheet peeling unit 20 abut on the photosensitive drum 10 before the sheet peeling unit 20 performs the peeling operation on the first of the 50 sheets. Thereafter, after the sheet peeling unit 20 completes the peeling operation on the last sheet of the 50th sheet, the sheet peeling unit 20 is separated from the photosensitive drum.

  In the present invention, the exact timing at which the sheet peeling unit 20 is brought into contact with the photosensitive drum 10 is not particularly limited. For example, the sheet peeling is performed at the timing when the leading edge of the first sheet reaches the peeling point P2. The unit 20 may be brought into contact with the photosensitive drum 10. This timing can be obtained by the method described above.

  In the present invention, the exact timing at which the sheet peeling portion 20 is separated from the photosensitive drum 10 is not limited in the same manner. For example, the timing at which the leading edge of the last sheet lands on the endless belt 13a, or the last The sheet peeling unit 20 may be separated from the photosensitive drum 10 at the timing when the trailing edge of the sheet passes the peeling point P2. These timings can also be obtained by the method described above.

  As described above, in this modification, the control unit 50 keeps the sheet peeling unit 20 in contact with the photosensitive drum 10 while the transfer unit 13 continuously transfers the toner image onto a plurality of sheets. It is the composition to do. According to this configuration, even when the sheet conveyance speed fluctuates due to disturbance, the separation / contact timing of the sheet separation unit 20 is not delayed, so that the sheet can be reliably separated without causing a jam. Can do. As a result, it is possible to prevent the jammed paper from scratching the peripheral surface of the photosensitive drum, and to prevent the toner from scattering in the image forming apparatus 1 due to the occurrence of the jam. Can do.

  From a different point of view, the present invention provides a transfer means for transferring a visualized and multi-image information formed on a latent electrostatic image bearing member (photosensitive member) using toner. In the image forming apparatus for fixing the image information transferred onto the paper to the paper by the thermal fixing means, the transfer means conveys the conveyed paper in a state of being wound around the photosensitive member. The image forming apparatus is characterized in that the angle of the sheet peeling claw disposed on the outer periphery of the photosensitive member to be prevented is that the angle formed by the transfer point of the transfer means and the sheet peeling point is at least 30 degrees or less. It can be said.

  In this image forming apparatus, the transfer unit is composed of a driving / driven roller that bridges the endless belt, and a conductive roller having a predetermined elastic force is disposed on the back surface of the endless belt in contact with the photoreceptor. It can be said that there is.

  Further, it can be said that the inclined surface (Y) of the guide portion after the paper of the peeling claw is peeled is in the state of facing the endless belt in the paper transport direction.

  Further, the peeling claw has a contact / separation mechanism with respect to the photosensitive member, contacts the photosensitive member at a timing when a printing request is made to the apparatus, and is separated from the photosensitive member at a timing when the printing request is completed. It can also be said.

  Alternatively, the peeling claw has a contact / separation mechanism with respect to the photoconductor, and comes into contact with the photoconductor when the leading edge of the conveyed paper enters the transfer region, and the leading edge of the paper is peeled off by the peeling claw. It can also be said that the sheet is separated from the photoreceptor at the timing when the leading edge of the sheet lands on the endless belt.

  Hereinafter, the effectiveness of the image forming apparatus according to the above-described embodiment has been verified, and the result will be described. In this example, when the conditions of the shape of the peeling claw, the diameter of the photosensitive drum, the paper conveyance speed, the paper interval, and the attachment angle (γ) of the paper peeling unit 120 described in the above embodiment are changed. Three items were examined: jam occurrence frequency during peeling, image degradation, and scratches on the photoreceptor surface. Here, the sheet conveyance speed is the same as the peripheral speed of the photosensitive drum. The results are shown in Table 1.

  In the “shape of the peeling claw” in Table 1, “conventional claw” means a peeling claw having an inclined surface X shown in FIG. 7 (that is, a peeling claw in the prior art). 3 shows a peeling claw having an inclined surface Y shown in FIG. 3 (that is, a peeling claw in the present embodiment). In addition, “◎”, “○”, “△”, “×”, “XX” in “Experimental results” are “very good”, “good”, “normal”, “slightly bad”, “ "Bad". For example, for “peeled jam”, “◎” means “very little jam”, “○” means “little jam”, “△” means “sometimes jam occurs”, “×” “Jam occurs to some extent”, “XX” indicates “Jam frequently occurs”. As for “deterioration of image”, the image deteriorates in the order of “◎”, “○”, “△”, “×”, “XX”, and “◎” indicates “very little image deterioration”, “ “XX” indicates that “the image is significantly deteriorated”. As for “scratches on the surface of the photoconductor”, the occurrence of scratches increases in the order of “◎”, “○”, “△”, “×”, “XX”. “Small” and “xx” represent “remarkably flawed”.

As shown in Table 1, when the conventional peeling nails were used, the following trends (1) to (3) were observed.
(1) When the process speed (paper conveyance speed) is increased, the occurrence rate of jam increases, and the scratches on the photoconductor generated when the jammed paper is wound around the photoconductor also increases.
(2) When the diameter of the photosensitive member is increased, the number of sheets to be printed is inevitably increased, so that the paper conveyance speed is increased and the occurrence frequency of jam is increased.
(3) In the conventional nail shape, since the tip shape is acute with respect to the curvature of the photoconductor, the paper is entrapped in the photoconductor when a jam occurs, and the scratches increase.

On the other hand, in the case where the peeling nail of the present embodiment was used, the following trends (4) to (6) were observed.
(4) When the process speed is low with a small-diameter photoconductor, the peeling point is too close to the transfer area, so that the occurrence rate of jam is large and the image deterioration is also large.
(5) When the large-diameter photosensitive member has a high process speed, the peeling point is separated from the transfer region and is not affected by the transfer electric field, so that the occurrence rate of jam is low and the image is not deteriorated.
(6) The nail shape of this embodiment is particularly effective when the photoconductor has a large diameter and the process speed is high.

  The present invention is not limited to the above-described embodiment and its modifications and examples, and various modifications are possible within the scope of the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  In addition, it goes without saying that the present invention includes a numerical range other than the numerical range shown in the present specification as long as it is within a reasonable range that does not contradict the gist of the present invention.

  The present invention can be suitably applied to an image forming apparatus such as a copying machine, a printer, a FAX, or a complex machine using an electrophotographic system.

1 is a side view illustrating a configuration of a main part around a photosensitive drum of an image forming apparatus according to an embodiment of the present invention. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates an embodiment of the present invention, in which (a) is an enlarged view showing the shape of a sheet peeling portion, and (b) is a view showing the direction of an inclined portion provided on a peeling claw. FIG. 5 is an enlarged view showing each stage in which the sheet adsorbed on the photosensitive drum is peeled off by the sheet peeling portion according to the embodiment of the present invention. FIG. 2 is a view illustrating a separation mechanism of a sheet peeling portion according to an embodiment of the present invention. FIG. 9 is a side view illustrating a conventional technique and illustrating a configuration of a main part around a photosensitive drum of an image forming apparatus. FIG. 2A shows a conventional technique, FIG. 2A is an enlarged view showing a shape of a sheet peeling portion, and FIG. 2B is a view showing a direction of an inclined portion provided on a peeling claw. FIG. 9 is a view showing a conventional technique and is an enlarged view showing each stage in which the paper adsorbed on the photosensitive drum is peeled off by the paper peeling portion.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Photosensitive drum 13 Transfer unit (transfer means)
13a Endless belt 13b Conductive roller 20 Paper peeling part (peeling member)
50 Control part (separation / contact control means)
Y inclined surface

Claims (5)

A photosensitive drum on which the toner image is formed on the peripheral surface, and a transfer unit that transfers the toner image formed on the photosensitive drum to the sheet by contacting the lower peripheral surface of the photosensitive drum via the sheet; An image forming apparatus comprising: a peeling member that comes into contact with the peripheral surface of the photosensitive drum and peels the sheet on which the toner image is transferred by the transfer unit from the photosensitive drum;
The photosensitive drum has a diameter of 100 mm to 150 mm,
About the rotation axis of the photosensitive drum, or less angle of 25 ° or more 30 ° from the center of the contact portion of the transfer means in the circumferential surface of the photosensitive drum to the contact portion of the release member,
The transfer means includes an endless belt that contacts the photosensitive drum, and a plurality of rollers that bridge the endless belt,
One of the plurality of rollers is a driving roller that is rotationally driven by a driving motor. By rotating the driving roller, rollers other than the endless belt and the driving roller are driven and rotated by the driving roller. And
One of the rollers other than the driving roller is a conductive roller having elasticity provided so as to press the endless belt against the photosensitive drum, and the peripheral surface of the photosensitive drum with respect to the conductive roller. By applying a voltage having a polarity opposite to the charging polarity of the toner image formed on the sheet, the sheet is attracted to the endless belt and conveyed, and the toner image formed on the photosensitive drum is conveyed. To be transferred to the above sheet,
The sheet conveying speed is 400 mm / sec or more and 600 mm / sec or less, and the interval between continuously conveyed sheets is 20 mm or more and 75 mm or less,
The peeling member has an inclined surface that guides the leading edge of the sheet peeled from the photosensitive drum downward from the horizontal direction, and the leading edge of the sheet guided by the inclined surface is the photosensitive member of the endless belt. An image forming apparatus, wherein the image forming apparatus is configured to land at a position downstream of the contact portion with the body drum in the sheet conveying direction . A separation / contact control means for bringing the separation member into contact with or separating from the photosensitive drum;
2. The separation / contact control unit according to claim 1, wherein the separation member is kept in contact with the photosensitive drum while the transfer unit continuously transfers the toner image to the plurality of sheets. The image forming apparatus described. Further provided with a separation control means for separating the separation member from the photosensitive drum,
2. The separation / contact control unit according to claim 1, wherein when the transfer unit continuously transfers a toner image to a plurality of sheets, the separation member repeatedly contacts and separates the separation member for each sheet. The image forming apparatus described in 1. The separation / contact control means causes the peeling member to contact the photosensitive drum at a timing when the leading edge of the sheet reaches the contact portion between the photosensitive drum and the transfer means, and the leading edge of the sheet peeled from the photosensitive drum is an endless belt. The image forming apparatus according to claim 3 , wherein the peeling member is separated from the photosensitive drum at a timing of contact with the photosensitive drum. The separation / contact control means causes the peeling member to contact the photosensitive drum at a timing when the leading edge of the sheet reaches the contact portion between the photosensitive drum and the transfer means, and the trailing edge of the sheet is the photosensitive drum and the peeling member. The image forming apparatus according to claim 3 , wherein the peeling member is separated from the photosensitive drum at a timing when it passes through the contact portion.

Images