JP2008065255A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotographic image forming apparatus, designed so as to prevent a fixing machine from causing wrinkling or jamming, even with a recording sheet, the leading end of which has been greatly deformed is inserted. <P>SOLUTION: The image forming apparatus includes a projecting part 26, which is disposed on the upper face of a conveyance guide 23 used to guide paper P to a fixing nip formed in a pressure contact area between a heat roller 21 and a pressure roller 21, is formed over the entire area in the direction of the paper width or part of the area, and is used to guide the leading end of paper P further upstream than the fixing nip. The image forming apparatus also includes a forcible guide 27, which is disposed close to and toward above the projecting part 26, and guides the leading end of the paper, guided upward by the projecting part 26, after directing it toward the fixing nip. When the paper's leading end passes over the face of the projecting part 26 along the face of the forcible guide 27, and enters the fixing nip or reaches the position, immediately in front of the entrance of the fixing nip, the forcible guide 27 moves back to a retracting place where it is no longer in contact with the unfixed toner image on the paper P. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly to an image forming apparatus that reduces wrinkles and jams in a fixing device that is likely to occur on a recording sheet deformed by moisture absorption or drying.

  In recent years, paper used for image forming apparatuses such as an electrophotographic printing apparatus such as a laser printer and an electrophotographic copying machine has increased in number of recycled paper using waste paper in consideration of the global environment. However, such paper is easy to absorb moisture, and the natural paper moisture often deforms the leading edge 50 of the paper as shown in FIG. 3, for example, and in many cases, the paper is similarly deformed by natural drying.

  As shown in FIG. 4, the deformed sheet P is fed into a fixing nip portion (described later) of a fixing machine that fixes the toner image on the sheet P by pressure between the fixing rollers 20 and 21 or heat and pressure. In many cases, the paper P is wrinkled at the time of fixing, and paper jams (hereinafter referred to as jams) may occur due to the wrinkles generated by the fixing machine as well as the deformation of the paper itself. Therefore, there is a demand for an image forming apparatus that does not cause wrinkles or jams even when easily deformed paper such as recycled paper is used.

  An electrophotographic printing apparatus will be described as an example of a conventional image forming apparatus. FIG. 1 is an overall configuration diagram of a conventional electrophotographic printing apparatus. In FIG. 1, 1 is a paper cassette for storing paper P, 2 is a pick roller for separating paper from the paper cassette 1, 3 is for correcting skew of the paper P separated by the pick roller 2, and paper transport timing It is a registration roller for taking.

  Reference numeral 4 denotes a recording process mechanism, which will be described in detail later, and reference numeral 5 denotes a fixing device for fixing the toner on the paper P, a heat fixing method using a pair of a heating roller and a pressure roller or a pressure roller without heating. A paired pressure fixing system is used. Reference numeral 6 denotes a paper tray, which is a part for stacking and storing printed paper P discharged outside the apparatus, for example, face down.

  A specific configuration of the recording process mechanism 4 is that the periphery of the photosensitive drum 11 is subjected to image exposure with a charger 12 for uniformly charging the photosensitive drum 11, laser light, or the like, and an electrostatic latent image is formed on the photosensitive drum 11. An optical unit 13 for forming an image, a developing unit 14 for attaching charged toner to an electrostatic latent image formed on the photosensitive drum 11, and a transfer unit 15 for electrostatically transferring the toner image on the photosensitive drum 11 to the paper P. A drum cleaner 16 that collects the transfer residual toner on the photosensitive drum 11 from the photosensitive drum 11 is provided.

  In general, the surface of the photosensitive drum 11 is formed of an organic photosensitive member, an Se photosensitive member, an a-Si photosensitive member, or the like, and the charger 12 includes a corona discharger, a conductive brush charger, a conductive rubber roller charger, or the like. The optical unit 13 includes a laser optical system or an LED optical system, the developing device 14 includes a two-component magnetic brush developing device, a magnetic one-component developing device, a non-magnetic one-component developing device, or the like. The drum cleaner 16 is generally constituted by a blade cleaner system, such as a corona transfer device or a conductive roller transfer device.

  In the printing process with the above configuration, first, the surface of the photosensitive drum 11 is uniformly charged by the charger 12. Next, the surface of the charged photosensitive drum 11 is exposed by the optical unit 13 in accordance with a pattern corresponding to the image. In the exposed portion of the image on the photosensitive drum 11, the charging potential at the charger 12 is lowered to form an electrostatic latent image.

  When the surface of the photosensitive drum 11 on which the electrostatic latent image is formed passes through the developing device 14, the toner charged in advance in the developing device 14 adheres to the electrostatic latent image on the photosensitive drum 11 to form a toner image. The On the other hand, the paper P on which an image is printed is conveyed to a position where the toner image formed on the photosensitive drum 11 is transferred by the transfer unit 15 (hereinafter referred to as a transfer region).

  The transfer unit 15 is disposed relative to the photosensitive drum 11 with the paper P interposed therebetween, and the toner image on the photosensitive drum 11 is statically charged by charging the paper P with a polarity opposite to the toner charge by applying a transfer voltage. It is electrically transferred to the paper P.

  While the paper P carrying the toner image by transfer is passed through the fixing device 5, the unfixed toner image on the paper P is fixed by heating and pressurization in the fixing device 5, and the paper P on which the toner image is fixed. Is discharged to the paper tray 6 to complete a series of printing processes.

  On the other hand, the toner (transfer residual toner) remaining on the photosensitive drum 11 after the toner image is transferred onto the paper P is collected by the drum cleaner 16 and conveyed to the developing device 14 by a toner reflux mechanism (not shown) and thereafter. Or is stored in a waste toner tank (not shown) and discarded when the storage amount reaches a certain amount.

  The above is the configuration of the apparatus and a series of printing operations. For example, in the case of double-sided printing, when the paper P on which the toner image has already been fixed on the back side is sent to the fixing device 5, the paper P generated at the time of fixing the back side The paper P is smoothly fed to a mutual pressure contact portion (hereinafter referred to as a fixing nip portion) between the heating roller 20 and the pressure roller 21 due to curling (for example, downward bending) of the leading edge of the paper which is a deformed state of First, the leading edge of the sheet comes into contact with the outer peripheral surface of the pressure roller 21 rotating in the clockwise direction, and the leading edge of the sheet is inserted into the fixing nip portion in an unstable state in which the leading edge of the sheet is forcibly warped. Wrinkles may occur on the paper P after fixing.

  Conventionally, in order to avoid the occurrence of such wrinkles in the fixing machine, the leading edge of the sheet is formed at the center of the sheet width direction (direction perpendicular to the conveyance direction) of the upper surface of the conveyance guide that guides the sheet P to the fixing nip. Even in the case of the paper P with the curled portion, there is one in which a protruding guide is provided in order to prevent the position at which the front end of the paper reaches the fixing device 5 from falling below the position of the fixing nip (for example, Patent Reference 1).

  FIG. 2 is a diagram illustrating a sheet conveyance path around a conventional fixing device. In FIG. 2, the fixing device 5 includes a heating roller 20 having a heater 22 serving as a heat source therein, a pressure roller 21 that applies pressure to the paper P so as to face the heating roller 20 across the paper P, and both rollers. And a conveyance guide 23 having a protruding guide 24 for guiding the paper P to the fixing nip portion.

  The guide surface (paper contact surface) of the protruding guide 24 is formed such that an extension line in the traveling direction of the paper P is positioned above the position of the fixing nip, that is, on the surface of the heating roller 20.

  With the configuration as described above, the leading end portion of the sheet P on which the toner image on the photosensitive drum 11 has been transferred by the transfer unit 15 is fixed by the protruding guide 24 provided at the center in the sheet width direction on the top surface of the conveyance guide 23. It is guided to the fixing device 5 without being lowered below the position of the nip portion, and is smoothly fed into the fixing nip portion. Further, the paper P is nipped and conveyed at the fixing nip portion, and the toner image on the paper P is melted and fixed by heating and pressurization at the fixing nip portion, and then sent out from the fixing device 5.

The above-described protrusion guide 24 is provided at the central portion in the paper width direction of the upper surface portion of the conveyance guide 23. However, the protrusion guide 24 is provided over the entire area in the paper width direction or at intervals in the paper width direction. Some are provided (see, for example, Patent Document 2).
JP-A-6-130842 JP 2000-141797 A

  However, according to the conventional technique, even if the paper P has the paper leading end curled downward, the leading end of the paper is guided to the fixing device 5 by the protruding guide 24 without being lowered below the position of the fixing nip, so that the fixing nip smoothly Since the leading edge of the sheet can be inserted into the fixing nip portion without any difficulty in a stable state, the occurrence of wrinkles in the fixing device 5 can be avoided, but the leading edge of the sheet is greatly wavy or curled upward. In the case of the sheet P, the leading end of the sheet abuts against the surface of the upper heating roller 20, for example, so that a part or the whole of the leading end of the sheet is unreasonably warped and inserted into the fixing nip. Therefore, there is a problem that wrinkles and jams are likely to occur in the fixing device.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of preventing the occurrence of wrinkles and jams in a fixing device even when the recording sheet has a sheet tip that is greatly deformed.

  An image forming apparatus according to a first aspect of the present invention includes a pair of fixing rollers that sandwich and convey a recording sheet by rotation, and a conveyance guide member that guides the recording sheet to a fixing nip portion formed at a mutual pressure contact portion of both the fixing rollers. In the image forming apparatus for fixing the toner image on the recording sheet at the fixing nip portion, the upper surface portion of the conveyance guide member and the entire region or a part in the direction orthogonal to the sheet conveyance direction, A projection that guides the sheet leading edge of the recording sheet in an upward direction with respect to the position of the fixing nip, and a position that is provided above the projection and is guided in the upward direction by the projection. And a forcible guide member that guides the front end of the sheet toward the fixing nip.

  The image forming apparatus according to a second aspect is the image forming apparatus according to the first aspect, wherein the leading end of the sheet guided by the forcible guide member enters or is just before entering the fixing nip, or forcibly. In a period during which at least a part of the guide member is in contact with a predetermined print guarantee area of the recording sheet, the forcing guide member is further provided with a retracting means for moving to a retracted position where contact with the recording sheet is eliminated.

  The image forming apparatus according to a third aspect is the image forming apparatus according to the first aspect, wherein the protrusion and the forced guide member are both formed or surface-treated with a conductive material, and at least one of them is formed. It is configured to be connected to a frame ground (hereinafter referred to as FG) directly or via an electric resistor.

  According to the first aspect of the invention, the protruding portion guides the leading end of the sheet upward from the position of the fixing nip portion, and the leading end of the sheet guided in the upward direction is then set to a position above the protruding portion. Since the forcible guide member provided guides the head toward the fixing nip, even if the recording sheet is greatly deformed (large wavy, large upward curl, etc.), the recording sheet is Deformation is corrected by forcibly bending to the lower side sequentially. For example, if it is a wavy sheet leading end, it is extended in a direction perpendicular to the sheet conveying direction and becomes flat, and the upper curling sheet leading end. If this is the case, the leading edge of the sheet can be smoothly guided to the fixing nip by preventing the wrinkles and jams from occurring in the fixing machine. .

  According to the second aspect of the invention, when the guided sheet leading edge enters or immediately enters the fixing nip, or at least a part of the forcible guide member contacts a predetermined print guarantee area of the recording sheet. During this period, since the forced guide member is retracted, it is possible to prevent the forced guide member from rubbing the unfixed toner image on the recording sheet and causing printing disturbance.

  Further, according to the third aspect of the invention, at least the surface of the projection and the forced guide member is conductive, and at least one of them is connected to the FG directly or via an electric resistor. Static electricity such as contact charging and frictional charging generated on the protrusion and the forced guide member that come into contact with the sheet can be removed.

  In particular, in the case where at least one of them is connected to the FG via an electrical resistor, the recording sheet being conveyed straddles between the projection or the forcible guide member connected in such a form and the transfer region. Even in such a state, the leakage current that causes the voltage of the transfer device to leak to the FG through the recording sheet that is regarded as a kind of electric resistor (the resistance value changes depending on the moisture absorption state of the recording sheet). Since it can be suppressed, it is possible to reduce the influence on the recording process conditions (for example, transfer voltage), and it is possible to prevent a decrease in print quality.

  According to the present invention, the leading end of the sheet guided by the protrusions upward from the position of the fixing nip is directed toward the fixing nip by the forcible guide member provided at a position above the protrusion. Therefore, since the recording sheet is sequentially bent downward from the leading edge of the sheet, the deformation is corrected. Therefore, even if the recording sheet has a large deformation at the leading edge of the sheet, wrinkles and jams in the fixing device are corrected. Occurrence can be prevented.

(Example 1)
Embodiments of the present invention will be described below with reference to the drawings. FIG. 5 is a diagram showing a functional configuration around the fixing device according to the present invention, and FIG. 6 is a diagram showing a specific configuration of an embodiment around the fixing device of the image forming apparatus according to the present invention. Note that FIG. 6 does not cover the configuration required for the fixing device and its periphery, but is a diagram limited to the configuration related to the present invention for convenience of explanation.

  In FIG. 5, the pair of fixing rollers that sandwich and convey the paper P by rotation includes a heating roller 20 having a heater (not shown) serving as a heat source inside, and a pressure on the paper P facing the heating roller 20 across the paper P. A fixing nip portion (not shown) is formed at the mutual pressure contact portion between the heating roller 20 and the pressure roller 21.

  Immediately before the fixing nip portion (upstream side of paper conveyance), a conveyance guide 23 for guiding the paper P to the fixing nip portion is provided, and a paper leading end portion of the paper P is further provided on the upper surface portion of the conveyance guide 23. Has a projection 26 that guides the image upward from the position of the fixing nip. The protrusions 26 are provided in the entire region or a part of the direction (hereinafter referred to as the paper width direction) perpendicular to the paper transport direction (including a rib structure that is discontinuous and exists in a row in the paper width direction). The cross section (cross section parallel to the paper conveyance direction) of the portion 26 has, for example, an arc shape or a triangular shape on the upper surface side or a similar shape thereof.

  A forcible guide 27 is provided at an upper position close to the protrusion 26 to guide the paper leading end guided by the protrusion 26 in the upward direction toward the fixing nip. Further, the forcible guide 27 is forced when the leading end of the paper passes through the surface of the protrusion 26 and further passes through the surface of the forcible guide 27 ((a) in FIG. 5) to enter or immediately enter the fixing nip. In order to avoid printing disturbance caused by the guide 27 coming into contact with the unfixed toner image on the paper P, the guide 27 is retreated to a retreat position where the contact with the paper P is eliminated ((b) of FIG. 5).

  When the paper P, which is smoothly fed to the fixing nip portion, is conveyed by being sandwiched by the fixing nip portion, the unfixed toner image on the paper P is formed by heating and pressing at the fixing nip portion. Melt and fix. The paper P here is not limited to a general printing paper, but may be a label paper or an envelope.

  Next, a more specific description will be given with reference to FIG. In FIG. 6, the heating roller 20, the pressure roller 21, the conveyance guide 23, the protruding portion 26, and the forced guide 27 are the same as those described with the same numbers in FIG.

  The protrusions 26 and the forced guides 27 are formed or surface-treated with a material having high conductivity and high wear resistance to the paper P, such as stainless steel. The formation and surface treatment in that case need not be performed on the entire surface or the entire surface of the projection 26 and the forced guide 27 itself, but may be performed at least on a portion where contact with the paper P is performed.

  In FIG. 6, 25 a connected between the conductive portion of the protruding portion 26 and the FG has static electricity such as contact charging or frictional charging generated when the paper P contacts or slides on the protruding portion 26. It is a resistor for energizing the FG so that it is not accumulated in the FG. Further, the resistor 25a is applied to the transfer unit 15 even when the sheet P being conveyed is straddling between the transfer region where the transfer unit 15 (see FIG. 2) is located and the protrusion 26. The transfer voltage is a resistor having a predetermined value for suppressing a leak current that leaks to the FG via the projection 26 through the paper P that is regarded as a kind of electric resistor.

  In particular, when printing in a high-temperature and high-humidity environment, the resistance value of the paper P is lower than that in a low-temperature and low-humidity environment. Therefore, the resistance value of the resistor 25a is at least a value that takes into account the decrease. Some are preferred. The predetermined value of the resistor 25a is, for example, 10 MΩ to 500 MΩ.

  The resistor 25a may be replaced with a varistor. In this case, the varistor voltage is preferably a value that exceeds the predetermined transfer voltage of the transfer unit 15 and that is less than the electrostatic voltage value that does not cause a problem in the image forming apparatus. For example, the varistor voltage is within the range of 300 to 800V. It is preferable to use it.

  An arrangement structure in which the sheet P being conveyed does not straddle between the transfer area and the protrusion 26 (an arrangement in which the distance between the transfer area and the protrusion 26 is longer than the length of the sheet P). ), It is not necessary to insert the resistor 25a, and the protrusion 26 may be directly connected to the FG. If an intermediate conveyance roller or the like (including a conveyance belt) connected by FG is interposed between the transfer area and the protrusion 26, it is necessary to consider according to the FG connection status of the intermediate conveyance roller.

  That is, if the intermediate conveying roller is directly connected to the FG, it may be connected directly to the FG without providing the resistor 25a. On the other hand, if the intermediate conveying roller is connected to the FG via a certain resistor, the resistance value is taken into consideration. Then, the resistance value of the resistor 25a may be set by a known method.

  Next, 25b connected between the conductive portion of the forcible guide 27 and FG is basically the same resistance as the resistor 25a described above, so that the resistor 25a is replaced with the resistor 25b in the description of the resistor 25a. Further, since the protrusion 26 may be replaced with the forced guide 27, the description is omitted here.

  The resistor 25a from the protrusion 26 and the resistor 25b from the forced guide 27 can be connected to the FG as one common resistor. In this case, the resistance value is determined by a well-known method. In this case, a value different from the resistance value is set. Space saving and cost reduction can be expected by using one common resistor.

  Subsequently, 28 is a cam receiver that is connected to the forced guide 27 and can reciprocate, and 29 is in contact with the cam receiving surface of the cam receiver 28 and is centered on a drive shaft (not shown). An eccentric cam that reciprocates the cam receiver 28 by rotating itself (for example, counterclockwise), and moves the forced guide 27 to a standby position and a retracted position, which will be described later, in conjunction with the reciprocating movement of the cam receiver 28. It is something to be made.

  Further, 30 is a motor linked to the eccentric cam 29, and is a motor that rotationally drives the eccentric cam 29. 31 is a leading edge detection sensor that detects the leading edge of the paper P, and is linked to an optical sensor or lever. Any known sensor such as a mechanical sensor may be used. 32 is a forced guide drive that generates various predetermined timing times for moving the forced guide 27 to the standby position and the retracted position based on the tip detection signal from the tip detection sensor 31 to control the rotational drive of the motor 30. It is a control unit.

  Specifically, the forcible guide drive control unit 32 generates various timing times generated by counting from the leading edge detection signal so that at least a part of the forcible guide 27 does not come into contact with a predetermined print guarantee area of the paper P. Based on the above, the forced guide 27 is moved to a retracted position where it does not come into contact with the print guarantee area by the time when it is assumed that the print guarantee area of the paper P being conveyed has reached the contact area with the forced guide 27, and thereafter The forced guide 27 is moved to a standby position where the leading edge of the paper can be guided from the time when the print guarantee area passes the contact area to the time when the leading edge of the next paper reaches the forced guide 27. Control.

  Note that the print guarantee area varies depending on the paper size, but the margin sizes from the leading edge and the trailing edge of the paper to the print guarantee area in the paper transport direction are generally the same regardless of the paper size. is there. However, the margin size may vary depending on the apparatus, and is generally 4 to 5 mm from the front end surface of the paper, and 4 to 5 mm from the rear end surface of the paper.

  The forcible guide drive control unit 32 described above uses the leading edge detection signal from the leading edge detection sensor 31 as a timing for measuring various predetermined timing times. However, the paper detection signal already detected in the image forming apparatus or the paper sheet is detected. In the case of having a paper travel timing signal generated from the detection signal or the like, any one of these signals may be used as a timing for timing as long as a relative time shift can be taken into consideration. When these signals can be used, the tip detection sensor 31 can be omitted, so that space saving and cost reduction can be expected.

  Next, the operation in the above configuration will be described. As the initial setting of the forced guide 27, the forced guide drive control unit 32 sets the forced guide 27 to the standby position by the time when the leading edge of the paper P reaches the forced guide 27 at the latest. At this standby position, the leading edge of the forced guide 27 is positioned immediately before the fixing nip, and therefore the leading edge of the conveyed paper P passes between the protrusion 26 and the forced guide 27. As a result, it is smoothly guided to the fixing nip (FIG. 6A).

  Subsequently, the forcible guide drive control unit 32 determines that the timing corresponding to the leading edge of the sheet enters the fixing nip or immediately before entering from the leading edge detection signal from the leading edge detection sensor 31, that is, the print guarantee area of the sheet P is the forced guide 27. The motor 30 is rotationally driven when a predetermined time until the point in time at which it is assumed that the contact area has been reached is counted, and the eccentric cam 29 linked to the motor 30 is rotated halfway. The rotation of the eccentric cam 29 at this time is transmitted to a cam receiver 28 that is integral with the forced guide 27, whereby the cam receiver 28 moves backward, and the forced guide 27 retracts to the retracted position in conjunction with this backward movement (see FIG. 6 (b)).

  Timing at which the rear end of the sheet P near the end of fixing at the fixing nip reaches or just before reaching the fixing nip, that is, when it is assumed that the print guarantee area has passed the contact area with the forced guide 27 Until the next paper leading edge reaches the forcible guide 27, the motor 30 is rotationally driven, and the eccentric cam 29 linked to the motor 30 is half-turned. Rotate. The rotation of the eccentric cam 29 at this time is transmitted to the cam guide 28 integrally formed with the forced guide 27, so that the cam receiver 28 moves forward, and the forced guide 27 is set at the standby position in conjunction with this forward movement.

  By repeating the above operation, the sheets P sequentially conveyed are smoothly fixed. In order to control the half rotation of the eccentric cam 29 when the forcible guide 27 is moved to an appropriate standby position and retracted position, position detection is performed using a known sensor such as an optical sensor or a mechanical sensor. Good to do. The position detection in that case may be any of the rotational position of the eccentric cam 29 itself, the moving position of the cam receiver 28, the moving position of the forced guide 27, and the like.

  As described above, in the present exemplary embodiment, the leading edge of the sheet is guided upward from the position of the fixing nip by the protrusion 26, and the leading edge of the sheet guided upward by the protrusion 26 is then fixed by the forcible guide 27. Since the sheet P is guided toward the nip portion, even if the sheet P has a large deformation (large wavy shape, large upward curl, etc.), the sheet P is forcibly bent downward sequentially from the leading end. Deformation can be corrected.

  For example, in the paper P in which the front end portion of the paper has a wavy shape, the front end portion of the paper is extended in the paper width direction due to the bending of the front end portion of the paper by the protrusion 26 and the forcible guide 27 (bowing downward). For paper P that is flattened and directed to the fixing nip portion, and the paper leading end is curled upward, the leading end of the paper P is directed to the fixing nip portion in the downward direction due to the same curving, etc. Since the deformation is corrected and smoothly guided to the fixing nip portion, the occurrence of wrinkles and jams in the fixing machine can be prevented.

  Further, since the leading edge of the paper does not hit against the roller surface of the heating roller 20 or the pressure roller 21, wrinkles and jams in the fixing machine caused by bending of the leading edge of the paper due to the bump (such as tip burrs and dog ears). Can be prevented.

  Further, when the leading edge of the sheet enters or is just before entering the fixing nip portion, the forced guide 27 is retracted to the retracted position, so that the forced guide 27 is caused to come into contact with the unfixed toner image in the print guarantee area. Disturbance can be avoided and deterioration of print quality can be prevented.

Overall configuration diagram of a conventional electrophotographic printing apparatus A diagram for explaining a sheet conveyance path around a conventional fixing device Paper deformed by moisture absorption Paper entering the fixing nip 1 is a diagram showing a functional configuration around a fixing device according to the present invention. FIG. 3 is a diagram showing a specific configuration of an embodiment around the fixing device of the image forming apparatus according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Paper 4 Recording process mechanism 5 Fixing machine 11 Photosensitive drum 13 Optical unit 14 Developing machine 15 Transfer device 20 Heating roller 21 Pressure roller 22 Heater 23 Conveyance guide 24 Protrusion guide 25a, 25b Resistance 26 Protrusion part 27 Compulsory guide 28 Cam receiver 29 Eccentric cam 30 Motor 31 Edge detection sensor 32 Forced guide drive controller 50 Paper edge

Claims (5)

A pair of fixing rollers that pinch and convey the recording sheet by rotation; and a conveyance guide member that guides the recording sheet to a fixing nip formed at a mutual pressure contact portion between the two fixing rollers. In an image forming apparatus for fixing a toner image on a recording sheet,
A protrusion that is provided on the upper surface of the conveyance guide member and in the whole area or a part of the direction orthogonal to the sheet conveyance direction, and guides the sheet leading edge of the recording sheet upward from the position of the fixing nip. ,
A forcible guide member that is provided at a position above the protruding portion and guides the sheet leading end portion guided in the upward direction by the protruding portion toward the fixing nip portion;
An image forming apparatus comprising: Retreating means for moving the forcible guide member to a retreat position where contact with the recording sheet is eliminated when the leading end of the sheet guided by the forcible guide member enters or immediately enters the fixing nip portion;
The image forming apparatus according to claim 1, further comprising: The protrusion and the forced guide member are
2. The image forming apparatus according to claim 1, wherein both are formed or surface-treated with a conductive material, and at least one of them is directly connected to a frame ground. The protrusion and the forced guide member are
The image forming apparatus according to claim 1, wherein both are formed or surface-treated with a conductive material, and at least one of them is connected to the frame ground via an electric resistor. The retracting means is
The image forming apparatus according to claim 2, wherein the forcible guide member is moved to the retracted position during a period in which at least a part of the forcible guide member is in contact with a predetermined print guarantee area of the recording sheet.

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