JP2005208540A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing the transfer defect of a developer in a sheet material while minimizing the reduction in a sheet conveyance speed. <P>SOLUTION: The image forming apparatus 1 is provided with a photoreceptor 4 on which the developer image to be transferred to a paper sheet is formed, a transfer roller 8 which transfers the developer image formed on the photoreceptor 4 to the paper sheet conveyed at a prescribed conveyance speed in a paper sheet conveyance path 15, a fixing roller 20 which is so controlled as to be rotated at a set speed determined according to the paper sheet conveyance speed and conveys the paper sheet existing on the downstream side of the transfer roller 8 in the paper sheet conveyance path 15 to the downstream side in the paper sheet conveyance direction while pinching the paper sheet therebetween, and a controller 50 which regulates the target value of the rotating speed of the fixing roller 20 while pinching the front end of the paper sheet to the speed lower than an ordinary set speed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that records a developer image corresponding to image data on a sheet material.

  The sheet material conveying operation is roughly classified into a sheet feeding system conveying operation for guiding a sheet from the sheet feeding unit to the image forming unit and a sheet discharging system conveying operation for guiding the sheet to the sheet discharging unit via the image forming unit. . The paper feed system transport operation is performed by a paper feed system transport roller including a pickup roller and a paper feed roller. On the other hand, the paper discharge system transport operation is performed by a paper discharge system transport roller including a registration roller, a transfer roller, a fixing roller, and a paper discharge roller. In the image forming apparatus, one of the conditions necessary for preventing the occurrence of image formation defects is to convey the sheet material at an appropriate conveyance speed during the paper discharge system conveyance operation.

  The sheet material during the paper discharge system conveyance operation is sent out downstream in the sheet conveyance direction while being sandwiched between a plurality of paper discharge system conveyance rollers arranged along the sheet conveyance path. Therefore, it is important to appropriately control the rotation speed of these paper discharge system transport rollers in order to obtain an appropriate transport speed of the sheet material during the paper discharge system transport operation. Here, as a general rule, the rotation speed of the transport roller during the paper discharge system transport operation is set so as to match the rotation speed of the image carrier in the image forming unit.

  However, in the high-speed image forming apparatus, the rotation speed of the image carrier is also increased. For this reason, the conveyance speed of the sheet material during the paper discharge system conveyance operation increases as the rotation speed of the image carrier increases. As a result, the sheet material on which the image is formed collides with a fixing roller which is one of the paper discharge system conveying rollers, and the vibration generated at this time may cause a problem in the transfer process of the developer to the sheet material.

  Therefore, in the prior art, in order to prevent the sheet material from vibrating due to the contact with the conveying roller, the rotation speed of the image carrier, the fixing roller at the stage before the leading edge of the sheet material passes through the fixing roller. There is a copying machine that reduces the rotation speed of the sheet and the conveying speed of the sheet material while synchronizing them (see, for example, Patent Document 1). According to this technique, it is possible to prevent the developer image transferred by the sheet material after transfer from colliding with the fixing roller from being blurred.

As another conventional technique for controlling the rotation speed of the paper discharge system conveying roller such as the fixing roller, the front end of the sheet material is positioned at the position where the heating device is disposed in order to sufficiently heat the front end to the rear end of the sheet material. When it reaches, there is a thermal fixing device and an image forming apparatus that reduce the conveyance speed of the subsequent sheet material (see, for example, Patent Documents 2 to 4).
JP-A 63-88569 JP-A-1-201688 JP-A-1-201689 JP-A-8-095424

  However, in the conventional techniques including the above-described Patent Documents 1 to 4, it is difficult to realize high-speed image forming processing because the period during which the sheet material conveyance speed is reduced is long. In particular, in recent years, high-speed image forming apparatuses that form images of 60 sheets or more per minute have appeared, and it is required to minimize the reduction in sheet material conveyance speed.

  An object of the present invention is to provide an image forming apparatus capable of preventing a transfer failure of a developer on a sheet material while minimizing a reduction in sheet conveyance speed.

  The present invention has the following configuration.

(1) an image carrier on which a developer image to be transferred to a sheet material is formed;
Transfer means for transferring the developer image formed on the image carrier to a sheet material conveyed at a predetermined conveyance speed in a sheet conveyance path;
A paper discharge system that is controlled to rotate at a set speed determined in accordance with the conveyance speed and conveys the sheet material positioned on the downstream side of the transfer unit in the sheet conveyance path to the downstream side in the sheet conveyance direction. Conveying means;
A speed control means for lowering the target value of the rotational speed of the paper delivery system transport means while sandwiching the leading end of the sheet material to be lower than the set speed;
It is provided with.

  In this configuration, the developer image formed on the surface of the image carrier is transferred to the sheet material by the transfer unit, and the sheet material to which the developer image has been transferred is moved downstream of the sheet conveyance path by the paper discharge system conveyance unit. Be transported.

  Here, as a typical example of the paper discharge system conveyance means, there are a transfer roller and a conveyance roller that conveys the sheet material on which the developer image is transferred to the transfer roller. As a general rule, the paper discharge system transport means is controlled to rotate at a preset speed. For this reason, when a disturbance such as an external force occurs and the rotation speed decreases, control is performed so that the rotation speed returns to the original set speed.

  In the present invention, when the leading end portion of the sheet material is sandwiched between the discharge system transport means, the target value of the rotation speed of the discharge system transport means becomes slower than the normal set speed. This takes into account the overshoot that occurs when control is performed to restore the paper transporting means whose rotational speed has fallen due to the load at the time of pinching the leading edge of the sheet material. It is. Here, the overshoot refers to a phenomenon in which the rotation speed of the paper delivery system conveying means exceeds the set speed and becomes higher than necessary.

  Immediately after the leading end of the sheet material passes through the paper discharge transport means, the rotational speed of the paper discharge transport means is restored to the normal set speed.

(2) The paper discharge system conveying means is a pair of fixing rollers for fixing the unfixed developer image transferred onto the sheet material by the transfer means to the sheet material.

  In this configuration, a pair of fixing rollers are arranged on the downstream side of the transfer unit in the sheet conveyance path, and the target value of the rotation speed of the fixing roller is normally set when the leading end of the sheet material is held between the fixing rollers. Lower than the set speed.

(3) The speed control unit adjusts the target value of the speed of the paper discharge system transport unit to the set speed after a bend is formed on the leading end side of the sheet material held by the paper discharge system transport unit. It is characterized by.

  In this configuration, first, the target value of the rotational speed of the paper delivery system transporting means is made lower than the normal set value to reduce the rotational speed of the paper delivery system transporting means, and then the sheet material sandwiched between them After the bend is formed on the front end side of the paper, the rotation speed of the paper discharge system conveying means is returned to the normal set speed by the speed control means.

(4) The speed control means sets a target value of the speed of the paper discharge system transport means to be faster than the set speed after a bend is formed on the leading end side of the sheet material sandwiched by the paper discharge system transport means. It is characterized by adjusting to the set speed after returning.

  In this configuration, the rotational speed target value of the paper discharge system transporting means is set lower than the normal setting value to reduce the rotational speed of the paper discharge system transport means, and then the leading edge of the sheet material sandwiched between them After the deflection is formed on the side, the speed control means sets the rotation speed of the paper discharge system transport means to the post-return set speed that is faster than the normal set speed. The purpose of applying the post-return set speed is to eliminate the bending that has occurred in the sheet material before the trailing edge of the sheet material passes through the image forming position.

  The bending of the sheet material may cause the trailing edge of the sheet material that has passed through the image forming position to jump up, and a transfer deviation may occur due to the jumping up. For example, when the force from the image carrier and the transfer unit does not act on the rear end of the sheet material, the force that the bent sheet material returns to the original position acts on the rear end side of the sheet material. Due to the action of this force, the rear end side of the sheet material comes into contact with the image carrier, and the developer image is blurred, or the developer remaining on the surface of the image carrier is transferred to the sheet material and the sheet material is soiled. There was a risk of occurrence. In the present invention, by adopting the post-return set speed to eliminate the bending of the sheet material, the trailing edge of the sheet material is prevented from jumping up.

(5) The transfer means includes a transfer roller that is controlled to rotate at a predetermined peripheral speed,
The post-return set speed is a speed at which the sheet material transport speed in the paper discharge system transport means is 1.005 to 1.010 times the predetermined transport speed.

  In this configuration, the post-return set speed is set such that the sheet material conveying speed in the paper discharge system conveying means is 0.5% to 1% faster than the sheet material conveying speed in the image forming position.

  The reason for setting the post-return set speed within this range is that when the sheet material conveying speed in the paper discharge system conveying means is 1% or more faster than the sheet material conveying speed in the image forming position, the sheet material is developed to the rear end side. This is because the front end of the sheet material is pulled quickly while the agent image is being transferred, and transfer deviation easily occurs on the rear end side of the sheet material. On the other hand, if the sheet material conveying speed in the paper discharge system conveying means is not about 0.5% faster than the sheet material conveying speed in the image forming position, the sheet material is conveyed at the leading end side faster than the trailing end side. This is because the bending generated in the sheet is difficult to be eliminated.

(6) The speed control means applies the first post-return set speed when the length of the sheet material in the sheet conveyance direction is equal to or less than a predetermined value, and the length of the sheet material in the sheet conveyance direction has a predetermined value. When exceeding, apply the set speed after the second return,
The first post-return set speed is a speed at which the sheet material conveying speed in the paper discharge system conveying means is 1.005 to 1.010 times the predetermined conveying speed,
The second post-return set speed is lower than the first post-reset set speed, and the sheet material transport speed in the paper discharge system transport means is approximately 1.005 times the predetermined transport speed. It is characterized by speed.

  In this configuration, it is determined whether to apply the first post-return set speed or the second post-reset set speed based on whether the length of the sheet material in the sheet conveyance direction is equal to or greater than a predetermined value. Is done. A typical example of the predetermined value is the length (about 216 mm) in the short direction of an A4 size sheet material.

  The reason for adopting two types of post-return set speeds is that the amount of bending that occurs in the sheet material changes depending on the length of the sheet material in the sheet conveyance direction, and the ease with which the generated bending is eliminated also changes. .

  When the length in the sheet conveying direction is longer than 216 mm, as in the case of B4 size or A3 size sheet material, the bending caused by decelerating the paper discharge system conveying means is caused between the transfer means and the image carrier. It is easy to be eliminated before the rear end of the sheet material passes through. On the other hand, in the sheet material having a length in the sheet conveyance direction of 216 mm or less, the above-described bending is difficult to be eliminated.

  In the present invention, for a sheet material that is difficult to bend, the first post-return set speed at which the speed of the front end side and the rear end side of the sheet material increases is set as the target value of the speed of the paper discharge system conveying means. Thus, a state in which bending is easily eliminated is formed. On the other hand, for the sheet material in which the bending is easily eliminated, the second post-return set speed at which the speed on the front end side and the rear end side of the sheet material is reduced is set as the target value of the speed of the paper delivery system conveying means. .

(7) The speed control unit is configured to select the second sheet in the job based on the set speed, the rotation speed target value, and the post-return set speed applied to the first image forming process in a single job. The subsequent set speed, the rotational speed target value, and the post-return set speed are determined.

  In this configuration, in a single job, the setting contents applied to the first image forming process are used in the second and subsequent image forming processes. Do not perform independent control for each sheet material, considering that the conditions such as the size and type of the sheet material to be used are the same when conveying the sheet material continuously in a single job. I have to.

  The reason why the above control is limited to a single job range is that the sheet material used for different jobs may have different moisture content in the sheet material, and the rigidity of the sheet material will change. Because there is. If the rigidity of the sheet material changes, the load at the time of entering the paper discharge system conveying means changes, so it may be difficult to eliminate the bending generated in the sheet material by controlling under the same conditions.

(8) The speed control means lengthens the period during which the target value is lower than the set speed in proportion to the thickness or hardness of the sheet material sandwiched by the paper discharge system transport means. To do.

  In this configuration, the speed control means makes the target value of the rotational speed of the paper discharge system transport means lower than the normal set speed in proportion to the difficulty of bending of the sheet material held by the paper discharge system transport means. Increase the period.

(9) The transfer unit is a transfer roller disposed so as to be in pressure contact with the image carrier with a sheet conveyance path interposed therebetween.

  In this configuration, the transfer of the developer to the sheet material is performed by a transfer roller that is in pressure contact with the sheet material.

(10) The sheet conveying path is formed in a vertical direction from a paper feeding unit located at a lower part of the apparatus to a paper discharging part located at an upper part of the apparatus via a transfer position.

  In this configuration, the present invention is applied to an image forming apparatus in which a sheet conveyance path is formed in the vertical direction (hereinafter referred to as a vertical pass type image forming apparatus).

  In the vertical path type image forming apparatus, the leading edge of the sheet material is bent by its own weight, and the contact position between the sheet material conveying means for the leading edge agent of the sheet material and the sheet material is constant depending on the type of the sheet material. A unique problem arises. In this respect, the vertical path type image forming apparatus is different from the horizontal path type image forming apparatus in which the sheet conveyance path is formed in the horizontal direction.

  According to the present invention, the following effects can be obtained.

(1) It is possible to prevent the rotation speed of the paper discharge system conveying means from increasing due to the occurrence of overshoot. As a result, it is possible to prevent the transfer of the developer image to the rear end side of the sheet material from being hindered by the leading end side being pulled by the paper discharge system conveying means that has been speeded up.

  In addition, since the period during which the paper discharge system transporting unit decelerates is short, it is possible to prevent a decrease in the image forming processing speed.

(2) When the leading end side of the sheet material is nipped by the fixing roller and the developer is transferred to the trailing end side of the sheet material, the rotation speed of the fixing roller is significantly higher than the normal set speed. Can be prevented. For this reason, it is possible to prevent the sheet material from being pulled at the front end side by the fixing roller, and it is possible to prevent the occurrence of problems such as deviation in the transferred developer image.

(3) Due to the bending formed on the front end side of the sheet material, it is possible to prevent the force acting on the front end side of the sheet material from being transmitted to the rear end side of the sheet material. For this reason, even if the leading end side of the sheet material is pulled by the paper delivery system that has suddenly increased, it is possible to prevent the developer image transferred to the trailing end side of the sheet material from being displaced. Is possible.

(4) It is possible to make it difficult for the rear end side of the sheet material to jump up and to prevent transfer deviation on the rear end side of the sheet material.

(5) By changing the conveyance speed between the front end side and the rear end side of the sheet material, it is possible to easily eliminate the bending generated in the sheet material.

(6) Regardless of the size of the sheet material, it is possible to form a state in which the bending generated in the sheet material is easily eliminated.

(7) It is possible to reduce the load on the speed control means when performing image forming processing continuously.

(8) Regardless of the type of the sheet material, it is possible to form a bend on the leading end side of the sheet material sandwiched between the paper delivery system conveying means. As a result, it is possible to prevent the action of the force on the front end side of the sheet material from being transmitted to the rear end side and to prevent the transfer processing on the rear end side of the sheet material from being hindered.

(9) Since the transfer process is executed while securely holding the rear end side of the sheet material between the image carrier and the transfer roller, the transferred developer image is less likely to be displaced. In addition, since the rear end side of the sheet material is sandwiched between the transfer roller and the image carrier, the leading end side of the sheet material can be reliably bent.

(10) Even in a vertical pass type image forming apparatus that performs high-speed image forming processing, occurrence of transfer misalignment or the like can be suppressed.

  Hereinafter, an image forming apparatus 1 that is an embodiment of an image forming apparatus of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a configuration of an image forming apparatus 1 according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 includes an image forming unit 2 that performs image forming processing according to input image data, and a paper feeding unit 3 that supplies paper to the image forming unit 2. It is equipped with.

  An electrophotographic process section centered on a photoreceptor 4 as an image carrier is disposed at a substantially central portion of the image forming section 2. In the electrophotographic process section, a charging unit 5, an optical scanning unit 6, a developing unit 7, a transfer unit 8, and a cleaning unit 9 are disposed around the photoreceptor 4.

  The charging unit 5 uniformly charges the surface of the photoconductor 4. The optical scanning unit 6 exposes the surface of the photoconductor 4 to form an electrostatic latent image. The developing unit 7 includes a developer supply unit 10 and supplies the developer to the electrostatic latent image formed by the optical scanning unit 6 to form a developer image. The transfer unit 8 transfers the developer image formed on the surface of the photoreceptor 4 to a sheet. The cleaning unit 9 removes the developer remaining on the surface of the photoconductor 4 so that the next image can be formed on the surface of the photoconductor 4.

  The charging unit 5, the optical scanning unit 6, the developing unit 7, the transfer unit 8, and the cleaning unit 9 perform a charging process, an exposure process, a developing process, a transfer process, and a cleaning process. In this embodiment, the residual developer removed by the cleaning unit 9 is collected in the developer supply unit 10 of the development unit 7 and used again in the development process. Note that the present invention can also be applied to an image forming apparatus having a configuration in which the residual developer removed by the cleaning unit 9 is not recycled.

  The paper feeding unit 3 is disposed below the image forming unit 2 described above. The paper feed unit 3 includes four paper feed trays 11 to 14. Note that the number of paper feed trays in the paper feed unit unit 3 is not limited to four, and can be increased or decreased as necessary.

  In the paper feed unit 3, the paper feed tray 13 is arranged above the paper feed tray 14 arranged at the lowest position, and the paper feed tray 11 and the paper feed tray 12 are provided above the paper feed tray 13. ing. In the vicinity of the four paper feed trays 11 to 14, a first paper transport path 15 and a second paper transport path 16 for transporting the paper stored in the paper feed trays 11 to 14 to the image forming unit 2 are formed. ing.

  The first paper transport path 15 is for transporting the paper stored in the paper feed trays 11 to 13 to the image forming unit 2, and the second paper transport path 16 is stored in the paper feed tray 12. This is for conveying the printed paper to the image forming unit 2. The first paper transport path 15 extends in the vertical direction along the frame 17 formed in the paper feed unit unit 3, and the second paper transport path 16 extends in the horizontal direction along the frame 17. ing.

  Further, in the paper feed unit 3, the guide 15 a constituting a part of the first paper transport path 15 and the guide 16 a constituting a part of the second paper transport path 16 are rotatable with respect to the frame 17. Has been. Therefore, the first paper transport path 15 or the second paper transport path 16 can be opened to the outside by rotating the guide 15a or the guide 16a, and the first paper transport path 15 or the second paper can be opened. The sheet on the conveyance path 16 can be removed.

  FIG. 2 is an explanatory diagram illustrating a main part of functions of the image forming apparatus 1. The transfer unit 8 includes a transfer roller 8A. The transfer roller 8A is disposed on the opposite side of the photoconductor 4 with the paper conveyance path 15 interposed therebetween so as to be in pressure contact with the photoconductor 4. In this embodiment, the pressure contact portion between the photoconductor 4 and the transfer roller 8A is the transfer position. Further, here, the transfer roller 8A constitutes the transfer means of the present invention.

  A registration roller R is disposed on the upstream side of the transfer position in the paper conveyance path 15. The registration roller R adjusts the timing for conveying the sheet to the transfer position.

  On the other hand, on the downstream side of the transfer position in the paper conveyance path 15, a transfer device having a pair of fixing rollers 20 for fixing the unfixed developer image transferred to the paper to the paper is disposed. The fixing roller 20 includes a heating roller 21 and a pressure roller 22. Heat and pressure are transmitted to the paper by the heating roller 21 and the pressure roller 22, and an unfixed developer image attached on the paper is fixed on the paper. In the present embodiment, the fixing roller 20 constitutes a paper discharge system conveying unit of the present invention. The present invention is also applicable to the case where another transport roller is disposed between the transfer roller 8A and the fixing roller 20, and in this case, the other transport roller is used as the paper discharge system of the present invention. Conveying means is configured.

  The image storage device 1 further includes a motor M1, a motor M2, a motor M3, a drive circuit 52, a control unit 50, and a management table 51.

  The motor M1 transmits the rotational driving force to the registration roller R. A clutch (not shown) is provided between the motor M1 and the registration roller R. For this reason, it is possible to rotate the registration roller R at an arbitrary timing by controlling on / off of the clutch by the control unit 50.

  The motor M2 mainly transmits the rotational driving force to the photoconductor 4. The motor M3 mainly transmits the rotational driving force to the heating roller 21 and the pressure roller 22. The drive circuit 52 drives the motor M1, the motor M2, and the motor M3. The drive circuit 52 rotates the motor M1, the motor M2, and the motor M3 at a desired speed based on the control signal from the control unit 50. Normally, the rotational speeds of the motor M1, the motor M2, and the motor M3 are controlled to be a set speed V1 that is determined according to the paper conveyance speed.

  The management table 51 stores information on rotational speeds to be applied to the motor M1, the motor M2, and the motor M3. Specifically, the management table 51 stores a rotation speed to be applied to the motor M1, the motor M2, and the motor M3 for each of a plurality of types of sheet materials having different thicknesses and hardnesses. The control unit 50 comprehensively controls each unit of the image forming apparatus 1.

  FIG. 3 is a flowchart showing a processing procedure for fixing roller speed control according to the present invention. First, when the image forming process is started, the control unit 50 starts the paper feeding operation by controlling the pickup roller, the paper feeding roller, and the conveying roller (S1). At this time, the sheet is conveyed to a contact position with the registration roller R.

  Subsequently, the control unit 50 waits until the timing at which the sheet should be conveyed to the transfer position (image formation timing) (S2). In the standby step of S2, when the image formation timing comes, the control unit 50 turns on the clutch between the motor M1 and the registration roller R to transmit the rotational driving force to the registration roller R (S3). Subsequently, the control unit 50 sets a built-in timer and starts measuring time (S4). FIG. 4 shows a state immediately after the registration roller R rotates.

  Subsequently, the control unit 50 stands by until the measured value t of the timer reaches t1 (S5). The value of t1 corresponds to the time from when the registration roller R starts to rotate until the leading edge of the sheet reaches the contact position with the fixing roller 20. Thereafter, the sheet that contacts the peripheral surface of the rotating fixing roller 20 is nipped by the fixing roller 20.

  Here, t1 is calculated based on the distance from the registration roller R to the fixing roller 20 and the conveyance speed of the image forming apparatus. Further, the value of t1 is also affected by the type of paper. In the vertical pass type image forming apparatus 1 as in the present embodiment, the timing at which the sheet and the peripheral surface of the fixing roller 20 come into contact with each other is earlier as the sheet is less thick and the stiffness is weaker. On the other hand, the thicker the paper is, the stronger the stiffness is, the later the timing at which the paper and the peripheral surface of the fixing roller 20 abut. This is because a sheet having a strong stiffness is not easily bent at the leading end and is guided straight to the nipping portion of the fixing roller 20 (the pressure contact portion between the heating roller 21 and the pressure roller 22). The management table 51 also stores information indicating the relationship between paper stiffness and time t1.

  Until the measurement value t of the timer measurement reaches t1, the sheet is conveyed downstream in the sheet conveyance direction while being sandwiched between the photosensitive member 4 and the transfer roller 8A as shown in FIG.

  In the standby step of S5, when the measured value t of the timer reaches t1, the control unit 50 outputs a control signal to the drive circuit 52, and sets the target value of the rotation speed of the fixing roller 20 to V2. Further, the control unit 50 resets the timer when the measured value t of the timer reaches t1. The target value V2 is a value lower than the set speed V1. In this embodiment, 75% of the set speed V1 is adopted as the target value V2. However, the range of the target value V2 is not limited to this value, and any value lower than the set speed V1 can be applied. FIG. 6 shows the state at the moment when the measured value t of the timer reaches t1.

  Subsequently, the control unit 50 sets a built-in timer and starts measuring time again (S7). In step S7, the time during which the target value of the rotation speed of the fixing roller 20 is set to V2 is counted.

  Subsequently, the control unit 50 stands by until the measured value t of the timer reaches t2 (S8). Here, t2 is the time required for the sheet to bend. Since the time t2 varies depending on the type of paper such as the thickness and hardness of the paper, the control unit 50 refers to the management table 51 and sets the optimum time according to the type of paper as t2. In the standby step of S8, when the measured value t of the timer reaches t2, the control unit 50 adjusts the target value of the rotation speed of the fixing roller to the set speed V1 (S9). When the measured value t of the timer reaches t2, the control unit 50 resets the timer. FIG. 7 shows a state where the target value of the rotation speed of the fixing roller 20 is set to V1 and the sheet is conveyed.

  Subsequently, the control unit 50 performs a discharge operation using the fixing roller 20 and the paper discharge roller, discharges the paper on which the image forming process has been performed, to the outside of the image forming apparatus 1, and ends the image forming process (S10).

  FIG. 8 shows an example of control of the rotation speed of the fixing roller 20. V1 is a target value of the rotation speed of the fixing roller 20, and corresponds to a set speed determined according to the sheet conveyance speed. V2 is also a target value of the rotation speed of the fixing roller 20, and is a speed lower than V1. In the figure, NT indicates the timing when the fixing roller 20 pinches the sheet. FIG. 8A shows the rotation speed of the fixing roller 20 in the conventional vertical pass type high-speed image forming apparatus. After the rotational speed of the fixing roller 20 temporarily decreases due to a load when the paper is sandwiched, control is performed to restore the decreased rotational speed to the target value. In this control, conventionally, the target value has been set to the set speed V1, and thus overshoot may occur in the rotational speed of the fixing roller 20.

  FIG. 8B shows the rotation speed of the fixing roller 20 in this embodiment. In the present embodiment, the target value while the fixing roller 20 holds the leading edge of the sheet is set to V2 lower than V1. As a result, as shown in FIG. 8B, the occurrence of the above-described overshoot is suppressed.

  FIG. 8C shows a change in the target value of the rotation speed of the fixing roller 20 in the present embodiment. Normally, the speed control shown in FIG. 8C is performed. However, as shown in FIG. 8D, even if the target value is set to 0 while the fixing roller 20 holds the leading edge of the sheet, the speed control is performed. The effects of the invention can be obtained.

  FIG. 9 shows an example of control of the rotation speed of the fixing roller 20. The control of the rotation speed of the fixing roller 20 in FIG. 9 is basically the same as the control of the rotation speed of the fixing roller 20 shown in FIG. However, the control shown in FIG. 9 is different from the control shown in FIG. 8 in that the rotational speed V2 of the fixing roller 20 that has been decelerated is returned to V3.

  V3 is a speed for increasing the transport speed of the paper sandwiched between the fixing rollers 20 to 1.005 times the transport speed of the paper at the image forming position. The reason why V3 is applied to the rotation speed of the fixing roller 20 is to eliminate the bending that occurs in the sheet when the fixing roller 20 rotates at V2 until the sheet passes through the image forming position. If the deflection of the paper is eliminated before the paper passes through the image forming position, inconveniences such as the trailing edge of the paper jumping up and the developer image being disturbed when passing through the image forming position are unlikely to occur.

  In the present embodiment, the paper conveyance speed at the image forming position is 335 mm / sec, and the conveyance speed of the paper sandwiched between the fixing rollers 20 rotating at V3 is 337.3 mm / sec. In the present embodiment, an experiment was performed by changing the conveyance speed of the paper sandwiched between the fixing rollers 20 when obtaining an appropriate range of V3. As a result, it has been found that when the conveyance speed of the sheet sandwiched between the fixing rollers 20 is 1.005 to 1.010 times the conveyance speed of the sheet at the image forming position, the bending of the sheet is easily eliminated.

  Further, it has been found that the ease of eliminating the generated deflection changes depending on the length of the paper in the paper transport direction. When the length of the paper in the paper transport direction is 216 mm or less, the flexure of the paper is difficult to be eliminated, and when the length of the paper in the paper transport direction exceeds 216 mm, the flexure of the paper is easily eliminated. For this reason, when the paper length in the paper transport direction is 216 mm or less, the rotation speed V3 of the fixing roller 20 needs to be faster than when the paper length in the paper transport direction exceeds 216 mm. In the present embodiment, when the paper length in the paper transport direction is 216 mm or less, the paper transport speed sandwiched between the fixing rollers 20 is within a range not exceeding 1.010 times the paper transport speed at the image forming position. V3 is increased as appropriate.

  When the length of the sheet in the sheet conveyance direction exceeds 216 mm, V3 is set so that the conveyance speed of the sheet sandwiched between the fixing rollers 20 is approximately 1.005 times the conveyance speed of the sheet at the image forming position. ing. In addition, about 1.005 times shall mean the range of 1.003 to 1.007 times here.

  Finally, the description of the above-described embodiment is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

1 is a diagram illustrating a configuration of an image forming apparatus of the present invention. It is a figure which shows the structure of the principal part of the image storage apparatus of this invention. It is a flowchart which shows the operation | movement procedure of the image storage apparatus of this invention. It is a figure which shows the conveyance state of the sheet material in the image storage apparatus of this invention. It is a figure which shows the conveyance state of the sheet material in the image storage apparatus of this invention. It is a figure which shows the conveyance state of the sheet material in the image storage apparatus of this invention. It is a figure which shows the conveyance state of the sheet material in the image storage apparatus of this invention. An example of control of the rotation speed of the fixing roller is shown. 6 shows another example of controlling the rotation speed of the fixing roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1- Image forming apparatus 4-Photoconductor 8-Transfer apparatus 20-Fixing apparatus 21-Heating roller 22-Pressure roller 50-Control part 51-Management table 52-Drive circuit

Claims (10)

An image carrier on which a developer image to be transferred to a sheet material is formed;
Transfer means for transferring the developer image formed on the image carrier to a sheet material conveyed at a predetermined conveyance speed in a sheet conveyance path;
A paper discharge system that is controlled to rotate at a set speed determined in accordance with the conveyance speed and conveys the sheet material positioned downstream of the transfer unit in the sheet conveyance path to the downstream side in the sheet conveyance direction. Conveying means;
A speed control means for lowering the target value of the rotational speed of the paper delivery system transport means while the leading edge of the sheet material is sandwiched, to be lower than the set speed;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the paper discharge system conveying unit is a pair of fixing rollers that fix the unfixed developer image transferred onto the sheet material by the transfer unit to the sheet material. apparatus.   The speed control means adjusts the target value of the speed of the paper discharge system transport means to the set speed after a bend is formed on the leading end side of the sheet material sandwiched by the paper discharge system transport means. The image forming apparatus according to claim 1.   The speed control means sets the target value of the speed of the paper discharge system transport means after the return higher than the set speed after a bend is formed on the leading end side of the sheet material sandwiched by the paper discharge system transport means. The image forming apparatus according to claim 1, wherein the image forming apparatus is adapted to a speed. The transfer means has a transfer roller that is controlled to rotate at a predetermined peripheral speed,
5. The post-return set speed is a speed at which a sheet material conveying speed in the paper discharge system conveying unit is 1.005 to 1.010 times the predetermined conveying speed. Image forming apparatus. The speed control means applies the first post-return set speed when the length of the sheet material in the sheet conveyance direction is less than or equal to a predetermined value, and when the length of the sheet material in the sheet conveyance direction exceeds a predetermined value, 2 Apply the set speed after returning,
The first post-return set speed is a speed at which the sheet material conveying speed in the paper discharge system conveying means is 1.005 to 1.010 times the predetermined conveying speed,
The second post-return set speed is lower than the first post-reset set speed, and the sheet material transport speed in the paper discharge system transport means is approximately 1.005 times the predetermined transport speed. The image forming apparatus according to claim 4, wherein the image forming apparatus is a speed.   The speed control means determines the second and subsequent sheets in the job based on the set speed applied to the first image forming process in the single job, the target value of the rotation speed, and the set speed after return. The image forming apparatus according to claim 4, wherein the set speed, the target rotational speed value, and the post-return set speed are determined.   The speed control means lengthens the period during which the target value is lower than the set speed in proportion to the thickness or hardness of the sheet material sandwiched by the paper discharge system transport means. The image forming apparatus according to any one of 1 to 7.   9. The image forming apparatus according to claim 1, wherein the transfer unit is a transfer roller disposed so as to be in pressure contact with the image carrier with a sheet conveyance path interposed therebetween.   10. The sheet conveyance path according to claim 1, wherein the sheet conveyance path is formed in a vertical direction from a paper feed unit located at a lower part of the apparatus to a paper discharge part located at an upper part of the apparatus via a transfer position. The image forming apparatus according to any one of the above.

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