JP2006349837A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To always form the appropriate loop of recording paper between a transfer part and a fixing part nip. <P>SOLUTION: A toner image on a photoreceptor drum 1 is transferred to a recording medium P by a transfer roller 4. The recording medium P conveyed by the transfer roller 4 is guided to a fixing device 7 by a conveyance guide 5. A loop detection sensor 20 detects the loop amount of the recording medium P guided by the conveyance guide 5. A CPU 30 controls a speed difference between recording medium conveying speed by the transfer roller 4 and the recording medium conveying speed by the fixing device 7 according to a result obtained by detecting the loop amount through controllers 32 and 33. Then, a means for making the recording medium P guided by the conveyance guide 5 generate force attracting the recording medium P to the conveyance guide 5 is provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a recording material by electrophotography. In particular, the present invention relates to a technique for controlling the conveyance of the recording material between a transfer unit and a fixing unit of an image forming apparatus.

  In a conventional image forming apparatus using an electrophotographic system, a toner image on an image carrier is transferred to a recording medium by a transfer unit, and then the recording medium is guided to a nip portion of a fixing device through a conveyance guide. . Here, in a state where the leading edge of the recording medium has entered the nip portion of the fixing device, the trailing edge portion may not yet pass through the transfer portion.

  On the other hand, there may be a difference between the paper conveyance speed in the fixing device and the paper conveyance speed in the transfer unit due to thermal expansion, solid difference of the pressure roller provided in the fixing device, or aging. In such a case, if the paper transport speed in the fixing unit exceeds the paper transport speed of the transfer unit, the recording medium carrying the unfixed toner image is pulled to the fixing unit side between the fixing unit and the transfer unit. This may cause image degradation. Therefore, if both transport speeds are controlled so as to form a loop as a slack in the recording medium transported between the transfer section and the fixing device, the above phenomenon can be prevented from occurring. Conversely, if the paper transport speed in the transfer section exceeds the fixing device paper transport speed, a loop (slack) more than necessary is formed on the recording medium. By forming more loops than necessary, the separation direction of the recording medium after image transfer in the transfer section and the incident angle of the recording medium to the fixing unit become unstable, so image scattering and fixing during transfer separation An offset or the like occurs in the instrument. Therefore, it is desirable that the recording medium is transported between the transfer unit and the fixing device while forming an appropriate loop. In order to form an appropriate loop between the transfer unit and the fixing unit, the paper conveyance speed in the transfer unit and the paper conveyance speed in the fixing unit are set to approximately the same speed, or the paper conveyance speed in the fixing unit is slightly set. It is necessary to set late.

  In this way, an appropriate loop is formed on the recording medium between the transfer unit and the fixing device to prevent the phenomenon that the recording medium is pulled, or an excessive loop is formed and excessively loosened, thereby preventing image deterioration. As a means for solving this problem, a loop detection sensor for detecting a loop of the recording medium is provided in the conveyance guide between the transfer unit and the fixing device, and from this result, the speed of the motor for driving the pressure roller of the fixing device is switched to perform recording. An image forming apparatus that controls the loop amount of a medium to be constant has been proposed.

  Examples of this type of image forming apparatus include those disclosed in Patent Document 1, Patent Document 2, and the like. Japanese Patent Application Laid-Open No. 2004-151867 discloses a conveying unit that conveys a recording medium that holds an unfixed toner image, a fixing unit that fixes the toner image on the recording medium using a pair of rollers, and a peripheral speed of the roller. And a speed control means for performing switching control between a first peripheral speed that is slower than a speed at which the transport means transports the recording medium and a second peripheral speed that is faster than the first peripheral speed. When the tip of the roller reaches the roller, the peripheral speed of the roller is set to the first peripheral speed, and after a predetermined time has elapsed, the peripheral speed of the roller is switched from the first peripheral speed to the second peripheral speed. An image forming apparatus was proposed.

  Patent Document 2 includes an image carrier driving device that rotationally drives an image carrier, and a roller driving device that drives a fixing roller of a fixing device that fixes a toner image transferred to a recording medium. In an image forming apparatus in which a distance between a transfer charger for transferring a toner image to a recording medium and the fixing roller is set to be shorter than a length of a transfer material, the recording medium to which the toner image is transferred is attached to a fixing roller. There has been proposed an image forming apparatus comprising a means for controlling the driving speed of the roller driving device to be slower than the driving speed of the image carrier driving device for a predetermined time immediately before entering.

  In Patent Document 3, a loop detection sensor for detecting a loop of a recording medium is provided in a conveyance guide between a fixing device and a transfer unit. When the loop amount of the recording medium is equal to or less than a predetermined amount, the transfer unit paper conveyance speed is determined. An image forming apparatus configured to control at a second fixing device paper conveyance speed that is faster than the transfer unit paper conveyance speed when the loop amount is detected to be a predetermined amount or more. Proposed.

  Patent Document 4 proposes an image forming apparatus in which the fixing entrance guide itself is biased by a spring force, and the loop amount of the recording medium is detected based on the swinging state and fed back to the fixing motor.

  Patent Document 5 proposes an image forming apparatus having a configuration in which a flag-shaped loop sensor is arranged in a fixing entrance guide, and a loop amount of a recording medium is detected by its ON-OFF output and fed back to a fixing motor.

Japanese Patent Laid-Open No. 62-161157 Japanese Patent Laid-Open No. 62-161182 Japanese Patent Laid-Open No. 5-107966 JP 2000-344385 A JP-A-2003-241453

  However, the above prior art technique has the following problems.

  When a flag sensor for detecting the paper loop amount is provided on the conveyance guide between the transfer unit and the fixing unit, stabilizing the behavior of the paper is very important in appropriately controlling the loop amount.

  The stabilization of the paper behavior mentioned here means how the paper is transported without being affected by the charging of the peripheral members. When the paper is affected by this, between the transfer portion and the fixing portion. There is a case where the paper feels like being conveyed in the air on the conveyance path. The influence of the charging of the peripheral members may be exerted even during the loop control in which the rotation speed of the fixing motor is controlled by the output of the sensor flag. In such a case, the loop control causes a malfunction and the printing surface side is The problem of getting dirty will occur.

  Here, the malfunction of the loop control will be described in detail. When the loop amount is detected using the normal sensor flag, it is assumed that an appropriate loop is formed. However, if the paper is lifted vertically by factors such as the influence of charging of the peripheral members and the restoring force of the spring attached to the sensor flag, and the sensor flag moves away from the back side of the paper, the paper is inherently too slack and fixed. However, since the sensor flag is not inclined, it is determined that there are few loops, and the paper conveyance speed of the fixing unit is reduced.

  Originally, the purpose is to stabilize the paper behavior (loop) by controlling the rotation speed of the fixing motor in accordance with the output of the sensor flag. If it is large, an image defect occurs as described above.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that does not cause image defects by stably detecting a loop amount between a transfer unit and a fixing unit and always forming an appropriate paper loop.

  An image forming apparatus according to the present invention transfers a toner image on an image carrier to a recording medium and transports the medium; fixes an unfixed toner image on the medium; and transports the medium A fixing unit that guides the recording medium conveyed by the transfer unit to the fixing unit, and a detection unit that detects an amount of a loop formed on the recording medium guided by the guiding unit. A control unit that controls a difference between a conveyance speed of the recording medium by the transfer unit and a conveyance speed of the recording medium by the fixing unit according to a detection result of the detection unit; and the guided recording medium And an attraction means for generating a force for pulling the lens toward the guide means.

  According to the apparatus of the present invention having the above-described configuration, an appropriate loop is stably formed on the recording medium that is guided between the transfer unit and the fixing unit by generating a force that draws the recording medium toward the guiding unit. Therefore, image scattering does not occur.

(Embodiment 1)
Apparatus Configuration FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus. The image forming apparatus of the present embodiment is a copying machine or a printer using a transfer type electrophotographic process.

  A photosensitive drum 1 which is an electrophotographic photosensitive member is used as an image carrier, and the photosensitive drum 1 is rotationally driven in the clockwise direction at a predetermined process speed (circumferential speed) in the drawing. The image forming apparatus main motor M1 drives the photosensitive drum 1 and the like. The controller 32 is controlled by the CPU 30 and controls the rotation of the motor M1.

  The photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the charging roller 2 during its rotation. The charged surface is exposed to light image L by an exposure device (not shown) to form an electrostatic latent image of target image information. Next, the latent image is visualized as a toner image by the developing device 3.

  A recording sheet (recording medium) P such as a copy sheet in which the toner image is fed at a predetermined timing from a sheet feeding section (not shown) to the photosensitive drum 1 and a transfer section T which is a pressure nip section of the transfer roller 4. Will be transferred sequentially. In the present embodiment, toner charged to a negative polarity is transferred to a recording medium by applying a transfer bias having a positive polarity.

  The recording paper P that has received the transfer of the toner image at the transfer portion T is separated from the surface of the photosensitive drum and is transported on the transport guide 5 to the heating type fixing device 7 described later. Therefore, the toner image is subjected to a heat fixing process and is output as an image formed product (copy, print).

  The surface of the photosensitive drum after the transfer of the toner image onto the recording paper P is subjected to a removal process of residual deposits such as transfer residual toner by the cleaner 6 and is repeatedly used for image formation.

  The conveyance guide 5 between the transfer unit T and the fixing device 7 is provided with a detection flag 21 for detecting the loop amount of the recording paper P. The detection flag 21 is made of a rod-like member that can swing around one end thereof, and the other end is disposed so as to protrude from the conveyance surface of the conveyance guide 5. The detection flag 21 is urged by a spring member (not shown) and swings according to the loop amount formed on the recording paper P. At one end of the detection flag 21 (the swing center of the detection flag 21), a flag extending toward the lower side of the transport surface is provided. This flag is linked to the movement of the detection flag 21 and loops the recording paper P. The optical path of the photo interrupter 22 for detecting whether or not the amount exceeds a predetermined value is blocked / opened. That is, the photo interrupter 22 is turned on / off according to the swing motion of the detection flag 21. The photo interrupter 22 and the detection flag 21 constitute a loop detection sensor 20 in cooperation with each other.

  The loop amount detected by the loop detection sensor 20 is the difference between the distance between two points and the distance between the two points where the recording paper P is actually connected with a loop. More specifically, when the conveyance speed Vf of the fixing device 7 is the same as the conveyance speed Vt of the transfer portion T, the distance between two points on the recording medium and the fixing device so that the recording paper P has a loop. 7 is a difference from the distance between two points on the recording medium when the conveyance speed Vf of 7 is controlled. Accordingly, when the conveyance speed Vf of the fixing device 7 is slower than the conveyance speed Vt of the transfer portion T, the loop amount increases, and when the conveyance speed Vf of the fixing device 7 is higher than the conveyance speed Vt of the transfer portion T, the loop amount decreases.

· Fuser fixing device 7 is a heating device of the pressure member driving type, tensionless type film heating system (JP-4-44075～44083 JP, No. Hei 4-204980～204484 Publication). The horizontally long stay 8 is made of a heat resistant resin and serves as an inner surface guide member of an endless heat resistant film (fixing film) 9 described below.

  The endless heat resistant film 9 is fitted on the stay 8 including the heater 40. The heater 40 has an electric resistance material (heating element) 42 such as Ag / Pd (silver palladium) approximately 10 μm thick on the surface of a substrate 41 made of alumina or the like, which is a high thermal conductivity material, along the longitudinal direction at a substantially central portion. , Coated to a width of 1 to 3 mm by screen printing or the like, and coated with glass or fluororesin as a protective layer 43 thereon.

  The pressure roller 50 forms a fixing nip portion N which is a pressure nip with the film 9 interposed between the pressure roller 50 and drives the film 9. The pressure roller 50 includes a metal core 51 made of aluminum, iron, stainless steel or the like, and a heat-resistant rubber elastic body 52 having good releasability such as silicon rubber which is sheathed on the shaft. In this embodiment, the thickness is 3 mm and the outer diameter is 20 mm. Further, a coating layer in which a fluororesin is dispersed is provided on the surface for the purpose of transporting the recording paper P and the fixing film 9 and preventing toner contamination.

  The end of the cored bar 51 is driven by the fixing device driving motor M2 so as to be rotated counterclockwise in the figure, and the inner surface of the endless heat-resistant film 9 is in close contact with the heater 40 by the driving force. It is driven to rotate clockwise while moving.

  More specifically, when the pressure roller 50 is driven to rotate, a moving force is applied to the film 9 by the frictional force with the rotary pressure roller 50 in the nip portion N, and the film 9 is substantially at the same speed as the rotational peripheral speed of the pressure roller 50. Then, the film inner surface is rotationally driven in the clockwise direction while sliding on the heater 40 surface (= protective layer 43 surface).

  When the recording paper P carrying an unfixed toner image enters the fixing nip portion N upward with the film driving and the heater 40 energized to the heating element layer 42, the nip In part N, the thermal energy of the heater 40 in contact with the inner surface of the film is applied to the recording paper P through the film 9, so that the toner is instantaneously melted. Then, the toner image is permanently fixed by pressurizing the molten toner onto the recording paper P at the nip portion N.

Motor drive The photosensitive drum 1 is rotationally driven by the main motor M1. The transfer roller 4 is connected to the photosensitive drum 1 through a gear, and is similarly rotationally driven using the main motor M1 as a drive source.

  The pressure roller 50 of the fixing device 7 is driven to rotate counterclockwise by the fixing motor M2, and the fixing film 9 is rotated by the rotation of the pressure roller 50. The motors of the main motor M1 and the fixing motor M2 are driven and controlled by the CPU 30 via the corresponding controllers 32 and 33, respectively.

  Here, the main motor M1 and the fixing motor M2 are controlled so that the recording medium conveyance speed becomes the process speed Vp (= 120 mm / sec).

Loop control The loop control of the speed difference between the conveyance speed of the recording paper P by the transfer roller 4 and the conveyance speed of the recording paper P by the step fixing nip portion N of the fixing device 7 will be described with reference to the flowchart of FIG. .

  Image formation is started (S22), and when the leading edge of the recording paper P enters the fixing device 7 (S24), loop control (S26) is performed. In the loop control, first, as shown in FIG. 3, the rotation speed of the fixing motor M2 is switched to R1, and the conveyance speed Vf of the fixing nip portion N is set to V1, which is slower than the conveyance speed Vt of the transfer portion T. (S260).

  Here, the rotation speed R1 of the fixing motor M2 is a rotation speed at which the conveyance speed V1 at the fixing nip portion N is slower than the conveyance speed V0 of the transfer portion T. The speed V1 is always V0 regardless of the situation in consideration of the type of the recording paper P, the number of continuous sheets to be passed, the thermal expansion of each component according to the fixing temperature control status, the variation of the applied pressure, the tolerance of the roller diameter, and the like. It is necessary to set so that> V1.

  The timing at which the leading edge of the recording paper P enters the fixing device 7 is calculated by the CPU 30 from the timing at which image formation is started. When the leading edge of the recording paper P is nipped by the fixing nip portion N via the detection flag 21, the conveyance speed Vf of the fixing nip portion N is set to a speed V1 that is slower than the conveyance speed V0 of the transfer portion T. Depending on the recording medium separation angle of the transfer portion N and the inclination angle of the fixing device 7, a downward convex loop is formed on the recording paper P. Further, the recording paper P is transported with its lower surface supported on the detection flag 21. Since the detection flag 21 is biased by the spring member as described above, the detection flag 21 does not swing to the position where the photo interrupter 22 is turned on until the loop amount of the recording paper P exceeds a predetermined amount.

  As the recording paper P further advances, the loop amount of the recording paper P gradually increases. When the loop amount exceeds a predetermined amount, the detection flag 21 swings against the urging force of the spring member, and the photo interrupter 22 is turned on. When it is detected that the photo interrupter 22 is turned on (yes in S262), the CPU 30 determines that the loop amount of the recording paper P has exceeded a predetermined amount, and switches the rotation speed of the fixing motor M2 from R1 to R2 ( S264). As a result, the conveyance speed Vf of the fixing nip portion N becomes V2, which is faster than the conveyance speed V0 of the transfer portion T, and the loop amount of the recording paper P between the transfer portion T and the fixing nip portion N gradually decreases.

  Here, V2 is also considered in the same manner as V1 described above, taking into account the type of recording paper P, the number of continuous sheets to be passed, the thermal expansion of each component according to the fixing temperature control status, the variation in pressure, the tolerance of the roller diameter, and the like. In any situation, it is necessary to set so that V0 <V2.

  If it is determined that the trailing edge of the recording paper P has passed through the fixing nip N (Yes in S266), image formation on the recording paper P is complete (S270), but has not passed (No in S266). If it is determined, the process is not completed, and the process returns to step S262.

  When the loop amount of the recording paper P is reduced to some extent, the detection flag 21 is swung in the returning direction, and the photo interrupter 22 is turned off. When it is detected that the photo interrupter 22 is turned off (no in S262), the CPU 30 determines that the loop amount of the recording paper P has become a predetermined amount or less, and switches the rotation speed of the fixing motor M2 from R2 to R1. If it is detected (S268). As a result, the conveyance speed Vf of the fixing nip portion N becomes V1, which is slower than the conveyance speed V0 of the transfer portion T, and the loop amount of the recording paper P between the transfer portion T and the fixing nip portion N increases again.

  In this way, by repeating the loop control for switching the rotation speed of the fixing motor M2 between V1 (hereinafter referred to as “Low”) and V2 (hereinafter referred to as “High”) in accordance with the on / off of the photo interrupter 22, the fixing portion M and the fixing portion are fixed. Image fixing is performed while the recording paper P is conveyed while the loop amount of the recording paper P between the nip portions N is maintained within a predetermined range.

  By repeating the above operation (S260 to 268) until the trailing edge of the recording medium passes through the fixing nip N, the recording paper is loosened (unnecessary loop) or pulled between the transfer portion T and the fixing nip N ( It is possible to maintain a conveyance state in which no shortage of loops occurs.

<Conventional example>
Here, the paper conveyance behavior in the conventional example will be described.

  PC-ABS is used as the material of the conveyance guide 5, and conveyance guide ribs 61 for reducing contact resistance are formed in the conveyance direction on the surface in contact with the recording paper P. A member for filling the space between the conveyance guide ribs 61 is not particularly provided, and the loop detection sensor 20 is provided at the center in the longitudinal direction as shown in FIG.

  Although the case where the loop detection sensor 20 is provided in the conveyance guide 5 is described here, the same idea is applied to the case where the loop detection sensor 20 is provided in the fixing entrance guide 62 made of resin.

  The loop control and paper transport behavior in the flow from the start of the image forming operation to the end of the image forming operation will be described with reference to FIGS.

  First, when an image forming start signal is input after the power of the image forming apparatus is turned on, the leading end of the recording paper P onto which the unfixed toner has been transferred is transferred to the transfer nip portion as shown in FIG. Exit.

  Thereafter, the recording paper P passes through the loop detection sensor 20 and enters the fixing nip N. However, in the conventional example in which there is no member that stabilizes the behavior of the recording paper P, the surrounding environment (particularly low humidity environment) Due to various factors such as rubbing of the peripheral member accompanying the image formation and the influence from the charging member, the peripheral substance existing in the conveyance space between the transfer portion T and the fixing device 7 is charged and due to electrostatic force, FIG. As described above, the leading edge of the recording paper P does not follow the conveyance guide 5 and feels like being conveyed in the air.

  Specifically, as shown in FIG. 5, it is particularly susceptible to the influence of the transfer surface side mold member 6a such as the toner cartridge cleaner 6 existing in the transfer space between the transfer portion and the fixing portion. When the mold member 6a) is charged, the recording paper P is attracted to the upper side under the influence. In addition, when a mold member exists above the conveyance space other than the above-described members, similarly, the effect of impairing the stability of paper conveyance is exerted.

  Next, when the leading edge of the recording paper P enters the fixing nip portion N and the loop control is started, the low speed R1 is first set. Here, when the recording paper P is conveyed in the air, if the loop detection sensor 20 is not tilted by a predetermined amount and the photo interrupter 22 is off, it is determined that the loop amount is small and the low speed R1 is set as it is. Will continue. On the other hand, when the loop detection sensor 20 is inclined by a predetermined amount and the photo interrupter 22 is in an on state while being conveyed in the air, it is determined that the loop amount is large and immediately switched to the high speed R2.

  After that, as described above, the motor rotation speeds of the low speed R1 and the high speed R2 are switched based on the output of the photo interrupter 22 according to the paper conveyance state, and the recording paper P is slack as shown in FIG. It will be transported without causing any tension or loop (shortage of loops).

  However, if the recording paper P receives an electrostatic force upward in the vertical direction under the influence of the charging of the peripheral members during the control of the motor rotation speed switching, the loop detection sensor suddenly occurs as shown in FIG. 20 may slip through the recording paper P and oscillate, causing malfunction.

  This malfunction is considered to be caused by the overlap of i) switching from R1 to R2, i i) electrostatic force acting on the recording paper P upward in the vertical direction, and iii) restoring force of the loop sensor spring.

  Once the loop detection sensor 20 passes through the recording paper P and enters the state shown in FIG. 8, the state of the photo interrupter 22 is turned off, and the loop amount is large, so that the high speed R2 should originally be set. Incorrectly set to Low speed R1. As a result, the sag on the upper side is further increased, and the printing surface side of the recording paper P is rubbed with the resin member installed on the upper side as shown in FIG.

<This embodiment>
In the first embodiment, the gap between the conveyance guide ribs 61 around the loop detection sensor 20 is filled with a conveyance sheet metal 63 made of SUS as shown by hatching in FIG. 10, and further, the conveyance sheet metal 63 is grounded to fix from the transfer portion T. The recording paper P guided to the nip N by the conveyance guide 5 is configured to generate a force that draws the recording paper P toward the conveyance guide 5. This force may be considered as an attractive force that acts between the recording paper P and the conveying sheet metal 63 due to static electricity. Other configurations and controls are the same as in the conventional example.

  Similar to the conventional example, the loop control and the paper transport behavior in the flow from the start of the image forming operation to the end of the image forming operation will be described with reference to FIGS. 2, 7, and 11 to 13.

  First, when an image formation start signal is input after the image forming apparatus is turned on, the leading end of the recording paper P to which the unfixed toner has been transferred is transferred to the transfer nip portion as shown in FIG. Exit.

  Thereafter, the recording paper P is guided by the conveyance guide 5 and passes through the loop detection sensor 20 and enters the fixing nip N (S24 in FIG. 2). At this time, since the conveyance sheet metal 63 exists on the conveyance guide 5, the recording paper P receives the electrostatic attraction force on the lower side and the behavior is stabilized, and the peripheral substances existing in the conveyance space between the transfer unit T and the fixing device 7. Even if (the above-described mold member or the like) is charged, the leading edge of the recording paper P is guided along the conveyance guide 5 as shown in FIG.

  Next, when the leading edge of the recording paper P enters the fixing nip portion N and the loop control (S26) is started, the low speed R1 is first set (S260). Here, since the recording paper P has been transported along the transport guide 5, the loop detection sensor 20 is inclined by a predetermined amount and the photo interrupter 22 is in an on state, so that it is immediately determined that the loop amount is large. Switch to High speed R2 (S262, 264).

  Thereafter, as described above, the motor rotation speeds of the low speed R1 and the high speed R2 are switched based on the output of the photo interrupter 22 according to the paper conveyance state (S262 to 268), and the recording paper P is slack as shown in FIG. (Necessary loops) and pulling (loop shortage) will be carried without causing.

  In the configuration of the present embodiment, even when the recording paper P receives an electrostatic force upward in the vertical direction under the influence of the charging of the peripheral member during the control of the motor rotation speed switching, the loop detection is suddenly detected. The sensor 20 does not slip through the recording paper P at all. Even if an upward force for lifting the recording paper P upward in the vertical direction according to i) to iii) described in the conventional example is applied, the recording paper P is moved downward toward the transporting sheet metal 63 on the transporting guide 5. This is considered to be due to the fact that the pulling force is applied and the upward force is canceled, and as a result, the malfunction of the loop detection sensor 20 passing through the recording paper P does not occur.

  Here, the electrostatic attractive force exerted on the recording paper P will be described in detail. The recording paper P is given a positive charge on the back of the paper in order to transfer the toner onto the recording paper at the transfer portion. The conveying surface side mold member such as the cleaner 6 in the upper portion of the conveying space is negatively charged, and an electrostatic attractive force to the side that draws the recording paper P upward works. The factors that cause the mold member to be negatively charged are due to the characteristics of the resin, the friction between the members, and the influence from the charging member.

  On the other hand, since the conveying sheet metal is grounded, a force acts on the side where the recording sheet P is drawn downward by electrostatic attraction between the recording sheet P and the conveying sheet metal. The behavior of the recording paper P is determined by the interaction of the electrostatic attraction force in two opposite directions upward and downward, and the weight of the paper. In the configuration of this embodiment, the conveyance sheet metal and the recording paper P are separated from each other. The distance is closer, and as the electrostatic attractive force, the downward force can overcome the information force, and the upward force can be canceled.

In order to quantitatively confirm the effect in the configuration of the conventional example and this embodiment, a comparative evaluation was performed under the following conditions.
Study environment: Low temperature and low humidity (15 ℃ / 10% RH)
Paper type: Office planner (A3)
Image pattern: Halftone Number of sheets passed: 200 sheets continuously The number of sheets that passed through the above conditions and the halftone image printing surface was rubbed and image defects occurred was counted. As a result, in the conventional example, an image defect was observed on 52 sheets out of 200 sheets. In this embodiment, no image defect was observed.

  As can be seen from this result, the behavior of the recording paper P is stabilized by applying a force that pulls the recording paper P downward in the vertical direction on the conveyance guide surface, and as a result, the control using the loop detection sensor 20 malfunctions. Control becomes possible.

  In the present embodiment, the conveyance sheet metal 63 is arranged between a part of the conveyance guide ribs 61 around the loop detection sensor 20, but the recording sheet P is further arranged by arranging the conveyance sheet metal 63 between all the conveyance guide ribs 61 as shown in FIG. 13. The behavior of is stable.

  In the case of the configuration using the conveying sheet metal 63 according to the present embodiment, the electrostatic force changes depending on the amount of charge on the back of the paper, so that the transfer bias applied to the transfer roller 4 or the downstream side of the transfer roller 4 is arranged. Even if the bias applied to the static elimination needle (not shown) is changed, a further effect can be obtained.

(Embodiment 2)
In the second embodiment, as shown in FIG. 14, the transport metal plate 63 is disposed between the transport guide ribs 61 on the downstream side of the loop detection sensor 20 in the transport direction. Other configurations are the same as those of the first embodiment.

  As a comparative example, as shown in FIG. 15, a sheet metal 63 is disposed between the conveyance guide ribs 61 on the upstream side of the loop detection sensor 20.

  Regarding the configuration of the present embodiment, loop control and paper transport behavior in the flow from the start of the configuration image forming operation to the end of the image forming operation will be described with reference to FIGS. 5, 7 to 9, 11, 15, and 16. To do.

  First, the paper conveyance behavior when the leading edge of the recording paper P onto which the unfixed toner has been transferred passes through the transfer nip portion is almost the same as that in FIG. 5 (conventional example).

  Thereafter, the recording paper P is guided by the conveyance guide 5, passes through the loop detection sensor 20, and enters the fixing nip N. At this time, since the conveying sheet metal 63 is on the downstream side of the loop detection sensor 20, although not as in the first embodiment, the recording paper P is subjected to an electrostatic force downward in the vertical direction and the behavior is stabilized, and the transfer portion T and the fixing portion are fixed. Even if the peripheral material existing in the transport space between the containers 7 is charged, the leading edge of the recording paper P is transported along the transport guide 5 as shown in FIG.

  Next, even when the leading edge of the recording paper P enters the fixing nip portion N and the loop control is started, the low speed R1 and the high speed R2 based on the output of the photo interrupter 22 corresponding to the paper conveyance state as in the first embodiment. Then, the motor rotation speed is switched, and the sheet is conveyed without causing slack (unnecessary loops) or pulling (loop shortage) as shown in FIG.

  In the comparative example of the transport sheet metal configuration shown in FIG. 15, the paper transport behavior when the leading edge of the recording paper P passes through the transfer nip T is the same as that of the first embodiment (FIG. 11) and is good. However, when the recording paper P passes through the loop detection sensor 20 and enters the fixing nip N, the loop detection sensor 20 suddenly removes the recording paper P as in the conventional example (FIGS. 8 and 9). A malfunction that slipped through occurred, and the printing surface side was rubbed with the resin member.

  The difference in paper conveyance behavior between the configuration of the present embodiment and the comparative example is speculative, but the positional relationship between the operating point where the loop detection sensor 20 and the recording paper P are in contact, the fulcrum of the loop detection sensor 20, and the conveyance sheet metal 63. It is thought that there is. That is, in the present embodiment, it is presumed that the loop detection sensor 20 can be pressed down more strongly by sandwiching the action point between the fulcrum and the conveying sheet metal 63 from the upstream side and the downstream side. On the other hand, the configuration as in the comparative example in which the fulcrum and the conveying sheet metal 63 are arranged on the same upstream side with respect to the action point is considered to have less force to press the action point downward than in this embodiment.

  In order to quantitatively confirm the effects in the configuration of the comparative example and the present embodiment, a comparative evaluation was performed under the same conditions as in the first embodiment. As a result, in the comparative example, image defects occurred on 20 sheets out of 200 sheets. In this embodiment, no image defect was observed.

  From the above results, it can be seen that the conveyance sheet metal 63 arranged between the conveyance guide ribs 61 is more effective in stabilizing the paper conveyance when arranged on the downstream side.

  In order to stabilize the paper transport behavior, it is preferable to dispose the transport metal plate 63 over the entire surface between the transport guide ribs 61 and apply a downward force over the entire surface of the recording paper. However, as in the present embodiment, the loop detection sensor 20 By providing the conveyance sheet metal 63 on the downstream side, the control using the loop sensor can be controlled without malfunctioning, and the member cost can be suppressed.

(Embodiment 3)
In the third embodiment, the conveying sheet metal 63 uses the configuration shown in FIG. 14 as in the second embodiment, and a bias is applied to the conveying sheet metal 63. Other configurations and controls are the same as those in the first embodiment.

  Since the transfer bias has a positive polarity, −1 KV was applied as a negative polarity as the bias applied to the transport metal plate 63. Since the transfer bias has a positive polarity, the back of the paper that has passed through the transfer portion T exhibits a positive polarity. Therefore, by selecting a negative polarity, the recording paper P is more attracted to the transport guide 5 and transported more stably. The

  In order to confirm the effect of the configuration of the present embodiment, evaluation was performed under the same conditions as in the first embodiment. As a result, in this embodiment, no image defect was observed in 200 sheets. Moreover, when the paper conveyance state was confirmed, it was also confirmed that the same stable behavior as in the first embodiment was exhibited.

  As can be seen from the above examination results, by adopting the configuration of the present embodiment, even when the occupation area of the conveyance sheet metal 63 is small, the force that draws the recording sheet P to the conveyance guide 5 side, that is, the lower side in the vertical direction is the recording sheet P. As a result, the paper behavior during conveyance can be stabilized, so that the control using the loop detection sensor 20 can be controlled without malfunctioning.

1 is a schematic configuration diagram of an image forming apparatus to which the present invention is applied. 6 is a flowchart of loop control of a conveyance speed of a transfer unit and a conveyance speed of a fixing device. 6 is a timing chart of a fixing device conveyance speed (fixing motor rotation speed) in loop control. It is a figure which shows the arrangement configuration of a loop detection sensor. FIG. 4 is a diagram illustrating a state where the leading edge of a recording sheet passes through a transfer nip portion. In the conventional example, it is a figure which shows a mode that the front-end | tip of a recording paper is conveyed on a conveyance guide. FIG. 6 is a diagram illustrating a state in which a leading edge of a recording sheet passes through a fixing device nip during loop control. In a prior art example, it is a figure which shows a mode that a loop detection sensor malfunctions. In a prior art example, it is a figure which shows a mode that a loop detection sensor malfunctions and image defect generate | occur | produces. It is a figure which shows the arrangement configuration of the conveyance sheet metal in Embodiment 1. FIG. FIG. 4 is a diagram illustrating a state in which the leading edge of the recording paper passes through a transfer nip portion in the first embodiment. FIG. 3 is a diagram illustrating a state in which the recording paper is guided to the vicinity of the fixing device nip in the first embodiment. It is a figure which shows another example of the conveyance sheet metal provided on a conveyance guide. It is a figure which shows the arrangement configuration of the conveyance sheet metal in Embodiment 2 and 3. FIG. It is a figure which shows the comparative example of the arrangement configuration of the conveyance sheet metal of Embodiment 2. FIG. 10 is a diagram illustrating a state in which the recording paper is guided to the vicinity of the fixing device nip in the second embodiment.

Explanation of symbols

1 Photosensitive drum (electrophotographic photosensitive member)
2 Charging roller 3 Developing device 4 Transfer roller 5 Conveying guide 6 Cleaner 7 Fixing device 8 Stay 9 Fixing film 20 Loop detection sensor 21 Detection flag 22 Photo interrupter 30 CPU
31 Storage Device 32, 33 Controller 40 Heater 41 Substrate 42 Heating Element Layer 43 Protective Layer 44 Thermistor 50 Pressure Roller 51 Core Shaft 52 Rubber Part 61 Conveying Guide Rib 62 Fixing Entrance Guide 63 Conveying Sheet Metal

Claims (8)

Transfer means for transferring the toner image on the image carrier to a recording medium and conveying the medium;
Fixing means for fixing an unfixed toner image on the medium and conveying the medium;
Guiding means for guiding the recording medium conveyed by the transfer means to the fixing means;
Detecting means for detecting the amount of loop formed in the recording medium guided by the guiding means;
Control means for controlling a speed difference between the conveyance speed of the recording medium by the transfer means and the conveyance speed of the recording medium by the fixing means according to a detection result of the detection means;
An image forming apparatus comprising: an attraction means for generating a force for drawing the guided recording medium toward the guide means.   The image forming apparatus according to claim 1, wherein the detection unit is a flag sensor provided in the guide unit.   3. The image forming apparatus according to claim 1, wherein the attraction unit is disposed downstream of the detection unit in the guide unit with respect to a conveyance direction of the recording medium.   The image forming apparatus according to claim 1, wherein the attraction unit is further arranged upstream of the detection unit with respect to the transport direction. The guide member has a plurality of conveying members for conveying the recording medium,
The image forming apparatus according to claim 1, wherein the attraction means is formed of a plate-shaped metal member, and the member is disposed between the plurality of conveying members.   The image forming apparatus according to claim 1, wherein the metal member is grounded.   The image forming apparatus according to claim 1, further comprising a bias unit that applies a bias voltage to the metal member. The image forming apparatus according to claim 7, further comprising a transfer bias unit that applies a transfer bias voltage to the transfer unit, wherein the bias voltage has a polarity opposite to the transfer bias voltage.

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