JP2005350245A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device preventing step-out of a stepping motor when reversely carrying and stably carrying a transfer paper for reversal carrying. <P>SOLUTION: The image forming device is provided with a plurality of pairs of reversal carrying rollers on a carrying passage, and these pairs of the reversal carrying rollers are respectively driven by motors. Among the motors, at least one motor is structured of a stepping motor. In the case wherein the transfer paper is pinched by each of the pair of reversal carrying rollers and stopped on the carrying passage, and then the carrying direction thereof is reversed, carrying by the pair of reversal carrying rollers, positioned upstream in the reversal carrying direction, with motor drive, is released. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and more specifically, to a reversing and conveying apparatus that prevents a stepping motor that drives a reversing and conveying roller of a transfer sheet from being stepped out.

  In recent image forming apparatuses, there is a demand for a function for forming an image on both sides of a transfer sheet or a reverse sheet discharge function for discharging a sheet with the image forming side of the transfer sheet facing down. In the image forming apparatus, a reverse conveyance mechanism is provided in the paper discharge path after fixing. For example, in the case of reverse paper discharge, instead of directly discharging the transfer paper image-formed on one side to the outside of the apparatus, it is once sent to the transport path configured for reversal, and again through the same transport path Discharge the transfer paper out of the machine. FIG. 5 is an explanatory diagram of the function of the transfer paper reverse conveyance mechanism.

  The reverse conveyance mechanism shown in FIG. 5 has a configuration in which a transfer paper conveyance path at the time of double-sided image formation and a conveyance path at the time of reverse discharge are partially shared at the rear end. This reversal transport mechanism has a transport path 50A for reverse paper discharge, a transport path 50B for re-feeding during double-sided image formation, and a transport path 50C used for reversing transfer paper during reverse paper discharge and double-sided image formation. The conveyance path 50A is provided with a reverse conveyance roller pair 52, and the conveyance path 50C is provided with a reverse conveyance roller pair 53. These reverse conveying roller pairs 52 and 53 are independently driven to rotate by a motor.

  The operation of such a reverse conveyance mechanism will be described below. The transfer sheet after one-sided image formation discharged from the fixing device is guided to the transport path 50A by a discharge path switching plate (not shown) and is transported toward the transport path 50C. On the way, the leading edge of the transfer paper passes through the branching point 56 to the conveyance path 50B, is nipped by the reverse conveyance roller pair 53, is driven by the reverse conveyance roller pair 53, and is sent into the conveyance path 50C.

  At the time of reverse paper discharge, the transfer paper usually stops with the leading edge of the transfer paper held between the reverse conveyance roller pair 53 and the rear end of the transfer paper passing through the paper discharge path switching plate and being held between the reverse conveyance roller pair 52. Thereafter, the rotational directions of both of the reverse conveying roller pairs 52 and 53 are reversed, and the conveying path 50A that has entered while being sandwiched between the two reverse conveying roller pairs 52 and 53 is conveyed in the reverse direction and is directly guided to the paper discharge unit. It is burned. As a result, the image forming surface is inverted downward and discharged.

  On the other hand, at the time of double-sided image formation, it is sandwiched between the reverse conveying roller pair 53 until the rear end of the transfer paper passes through the branch point 56 and conveyed to the inside through the conveying path 50C. The rear end of the transfer paper passes through the branch point 56 and stops in a state where it is nipped by the reverse conveying roller pair 53. Thereafter, the rotation direction of the reverse conveyance roller pair 53 provided on the conveyance path 50C is reversed, and the transfer sheet is sent to the conveyance path 50B to the image forming unit.

  In an image forming apparatus provided with such a reversal conveyance mechanism, a stable reversal conveyance operation is required in a short time in order not to lower the image forming speed, that is, the productivity of a copy. Therefore, a stepping motor that is extremely easy to perform reverse rotation control and speed control is often used to drive a plurality of reverse conveyance roller pairs that convey transfer paper.

  However, the stepping motor controls the rotation of the motor rotor by synchronizing with the rotating magnetic field, and there is a possibility of step-out depending on an excessive load fluctuation. For example, the movement of the transfer paper in the transport path is not constant due to the type of paper or the environment in the device, and it may be pulled by a pair of reverse transport rollers and pass the shortest distance. However, it may be transported easily.

  When the reverse conveying roller pair on the upstream and downstream sides in the conveying direction is driven by another stepping motor, if the conveying operation is only in one direction, provide a speed difference between the linear speeds of the respective reverse conveying roller pairs. It is possible to avoid a configuration in which the leading end side roller pulls the recording paper. However, when the transfer paper is reversed and held between a plurality of reverse conveyance roller pairs, when the reverse conveyance roller pair is stopped, it is not known whether the transfer paper is in a tensioned state or a slack state. There is a possibility that the transfer paper will be further pulled or pushed in due to the delay in response of the rise of the roller due to the backlash, and the stepping motor may step out due to the influence of these load fluctuations.

  As a solution to this problem, the transfer paper linear speed of each pair of reverse conveyance rollers is controlled to be highly the same so that adjacent reverse conveyance roller pairs do not pull or push each other, or upstream in the transfer paper conveyance direction. For example, a method in which the linear velocity of the pair of reverse conveying rollers positioned on the side is slightly increased to convey the transfer paper slightly pushed.

For example, in Patent Document 1, as an example, in consideration of variations due to dimensional tolerances of the transfer paper linear speed at each part of the transfer roller, the intermediate roller, and the fixing roller, the transfer paper being transferred is pulled by the fixing roller. Discloses a method for controlling the linear speed of the transfer paper of each roller so that any one of the slack amounts generated between the transfer roller and the intermediate roller and between the intermediate roller and the fixing roller does not become excessive. Has been.
JP-A-5-134499 (paragraph number 0008)

  However, no matter how the linear speed of the pair of reverse conveying rollers is controlled, variations in drive system parts (eg, motor, roller, transmission gear, etc.), rattling of the meshing part, wear or passage of transfer paper due to paper type The transfer paper may be pulled or loosened due to subtle misalignment of the path, etc. If pulling occurs, the load on the stepping motor becomes higher than expected, causing the stepping motor to step out. May not be prevented.

  In addition, when the transfer paper suddenly becomes excessively slack (loop of transfer paper), not only does the load fluctuate and the possibility of step-out increases, but it also rubs against the guide member facing the transfer surface. As a result, the image may be deteriorated or defective. In order to deal with these problems, a method of increasing the torque margin of the motor and controlling the linear velocity of the pair of reverse conveying rollers to a high degree can be considered, but the improvement of the motor torque margin leads to an increase in the motor standard size and the necessary consumption. Since the amount of power increases, the cost of the entire apparatus is unavoidable. In addition, the result is contrary to downsizing of the equipment.

  By the way, when considering a conventional reversal conveyance mechanism, the pair of reversal conveyance rollers 53 provided in the conveyance path 50C (see FIG. 5) has a conveyance force for the transfer paper when forming a double-sided image alone, and the conveyance path 50A. Since the reverse conveying roller pair 52 provided on the single sheet also has a transfer sheet conveying force at the time of reverse discharge, the reverse conveying roller pair 53 does not necessarily need the transfer sheet conveying force at the time of reverse discharge. On the contrary, if the conveying force is given to the reverse conveying roller pair 53 at the time of reversed paper discharge, the above-described transfer paper is pulled or pressed.

  The present invention has been made on the basis of such considerations. When the transfer sheet is reversed and discharged, the reverse conveyance roller pair positioned on the upstream side in the reversed conveyance direction is released to operate the reverse conveyance roller pair. An image forming apparatus capable of stably transferring transfer paper by eliminating the tension and pressing of the transfer paper by a plurality of pairs of transport rollers caused by timing shift, and consequently reducing the load fluctuation of the stepping motor and preventing step-out. The purpose is to provide.

  An image forming apparatus according to the present invention is a plurality of reverse conveying roller pairs provided on a conveying path, and each of the reverse conveying roller pairs is driven by a motor to convey transfer paper, and the motor Of these, at least one of the motors is a stepping motor. In order to achieve the above object, the image forming apparatus according to the invention of the present application reversely conveys the transfer sheet when the transfer sheet is sandwiched between the reversal conveyance roller pairs and stopped on the conveyance path, and then the conveyance direction is reversed. The reverse conveyance roller pair located on the upstream side in the direction is configured to cancel the conveyance by the motor drive.

  In the image forming apparatus according to claim 2, the pair of reversing conveyance rollers positioned upstream in the reversed conveyance direction in the image forming apparatus having the above configuration is driven by a driving roller driven by a motor and the driving roller. When the transfer paper transport direction is reversed on the reverse transport path, the motor-driven transport of the reverse transport roller pair is canceled by releasing the pressure-bonding state of the drive roller and the driven roller. It is configured as follows.

  In the image forming apparatus according to claim 3, the pair of reverse conveying rollers positioned on the upstream side in the reversed conveying direction in the image forming apparatus according to claim 1 is a driving roller driven by a motor via a clutch mechanism. And a driven roller that is driven by the driving roller, and when the transfer paper transport direction is reversed, the motor-driven transport of the pair of reverse transport rollers is released by releasing the coupling of the clutch mechanism. It is configured as follows.

  In the image forming apparatus according to claim 4, the pair of reverse conveying rollers positioned on the upstream side in the reversed conveying direction in the image forming apparatus according to claim 1 includes a driving roller driven by a stepping motor and a driving roller. When the transfer paper conveyance direction is reversed on the conveyance path, the conveyance of the reverse conveyance roller pair is canceled by the motor drive by cutting off the excitation of the stepping motor. It is configured.

  The image forming apparatus according to claim 5 is characterized in that, in any of the image forming apparatuses according to claims 1 to 4, the drive motors of the pair of reverse conveying rollers are all composed of stepping motors. . In the image forming apparatus having such a configuration, the following operational effects can be obtained.

  According to the image forming apparatus of the present invention, since the conveyance by the motor drive of the reverse conveyance roller pair positioned upstream in the reversed conveyance direction is released, the transfer paper is conveyed downstream in the reversed conveyance direction. This is performed only with the pair of reverse conveying rollers positioned. As a result, even if transfer paper is pulled or loosened (looped) when the forward rotation is stopped, it is not affected, and the linear speed of multiple reversing transport rollers is suppressed against load fluctuations. Therefore, stable transfer paper can be reversed and conveyed.

  In addition, the transfer paper is transported only by driving the pair of reverse transport rollers positioned downstream in the reverse transport direction, and the motor only needs to secure a torque corresponding to the original transport force. This problem can be avoided, and conversely, the cost of the motor drive circuit can be expected to be reduced by reducing the total current.

  According to the image forming apparatus of the second aspect, when the transfer direction of the transfer paper is reversed, the pressure-bonding state between the driving roller and the driven roller located upstream in the reversed conveyance direction is released. There is no pulling or looping of the transfer paper between the pair of conveying rollers, and the stepping motor step-out due to the pulling of the transfer paper or the like can be avoided. This makes it possible to stably transfer and transfer the transfer paper.

  According to the image forming apparatus of the third aspect, when the transfer paper transport direction is reversed, the connection state between the drive roller and the motor clutch mechanism is released. The stepping motor can be prevented from stepping out due to the pulling of the transfer paper. This makes it possible to stably transfer and transfer the transfer paper.

  According to the image forming apparatus of the fourth aspect, when the transfer direction of the transfer paper is reversed, the excitation of the stepping motor is cut off, so that the driving roller is released from the restraining force, and between the pair of reverse conveyance rollers. There is no pulling of the transfer paper, and step-out of the stepping motor due to the pulling of the transfer paper can be avoided. This makes it possible to stably transfer and transfer the transfer paper.

  According to the image forming apparatus of claim 5, even if all of the motors that drive the pair of reverse conveyance rollers are configured by stepping motors in order to improve the controllability of the reverse conveyance, the upstream side in the conveyance direction reversed at the time of reversal. Since the transfer by the stepping motor of the reverse conveyance roller pair positioned at the position of the reverse transfer roller is released, the transfer paper is not pulled between the reverse conveyance roller pair, and even if there are variations in the drive system parts, backlash, etc. Step out can be avoided.

  In addition, since the transfer paper is transported by driving the stepping motor of only the pair of reverse transport rollers positioned on the downstream side in the reverse transport direction, and the stepping motor only needs to secure a torque corresponding to the original transport force, the stepping motor is sufficient. The problem of an increase in the size of the motor can be avoided, and an excellent effect that power consumption can be reduced can be obtained.

  Hereinafter, an embodiment of the image forming apparatus 100 according to the present invention will be described with reference to FIG. This color image forming apparatus 100 is called a tandem type color image forming apparatus, and includes an endless belt-like intermediate transfer body 7 that is stretched by a plurality of roller groups and supported so as to be able to be driven around. Four image forming units 10Y, 10M, 10C, and 10K that form toner images of yellow, magenta, cyan, and black are arranged in tandem along the outer peripheral surface of the intermediate transfer member 7.

  The image forming units 10Y, 10M, 10C, and 10K have photoconductors 1Y, 1M, 1C, and 1K each having a latent image formed on the surface, respectively, and perform image formation along the outer peripheral surface of each photoconductor. In order of operation, charging devices 2Y, 2M, 2C, and 2K that charge the surfaces of the photoreceptors 1Y, 1M, 1C, and 1K almost uniformly, and an exposure device that writes an electrostatic latent image on the surface of each photoreceptor. 3Y, 3M, 3C, 3K, developing devices 4Y, 4M, 4C, 4K that transfer toner to each latent image formed on the surface of the photoconductor to form a toner image, and intermediate the toner image on the surface of each photoconductor Primary transfer devices 5Y, 5M, 5C, and 5K for transferring onto the transfer body 7 and cleaning devices 6Y, 6M, 6C, and 6K for cleaning the surface of the photoreceptor after transfer are disposed.

  The image reading unit 30 disposed on the upper part of the image forming apparatus 100 includes a scanning unit 31 including a light source and a mirror for illuminating a document, a traveling body 32 having two roof mirrors, an imaging lens 33, an image sensor 34, and the like. The document placement unit 35 is configured. The image sensor 34 is mainly composed of a CCD, and an optical image signal collected by scanning the light source of the scanning unit 31 is converted into digital image data for each color by an image processing unit (not shown), and then the exposure device 3Y, Sent to 3M, 3C, 3K.

  In the exposure apparatuses 3Y, 3M, 3C, and 3K, the semiconductor laser is electrically modulated based on each image data, and sub-scanning is performed by a polyhedral reflecting mirror (polygon mirror) and a lens group through a collimator lens. Further, the main scanning is performed by rotating the photoconductors 1Y, 1M, 1C, and 1K, and the electrostatic latent images are reproduced on the photoconductors 1Y, 1M, 1C, and 1K.

  Prior to exposure, a predetermined surface charge is applied to the photoreceptors 1Y, 1M, 1C, and 1K by corona discharge of the charging devices 2Y, 2M, 2C, and 2K. The electric charge is reduced according to the exposure amount, and as a result, electrostatic latent images corresponding to the image information data are formed on the respective photoreceptors 1Y, 1M, 1C, and 1K.

  The electrostatic latent image is visualized with toner of each color developer supplied from the developing devices 4Y, 4M, 4C, and 4K, and becomes a toner image. The toner images of the respective colors formed on the photoreceptors 1Y, 1M, 1C, and 1K are sequentially transferred to the same position on the intermediate transfer member 7 rotated by the primary transfer devices 5Y, 5M, 5C, and 5K, and synthesized. A color image is formed.

  On the other hand, a movable plate 23 that is lifted upward by lifting means is disposed at the bottom of the plurality of paper trays 20 that store the recording paper P. The movable plate 23 on which the recording paper P is placed receives the paper feed start signal and lifts the recording paper P to the upper limit position limited by the upper limit detection sensor. At the same time, the pickup roller 21 falls, and the uppermost recording paper P placed thereon is configured to contact the pickup roller 21.

  The recording paper P in contact with the pickup roller 21 is taken out of the paper tray 20 by the contact pressure, separated one by one by the reverse roller 22 and fed. The fed recording paper P is guided to the registration rollers 25 by being guided by a plurality of intermediate rollers 24. The transported recording paper P is fed to the secondary transfer roller 8 with the skew correction and feeding timing of the recording paper P taken by the registration roller 25, and the synthesized color image on the intermediate transfer body 7 is sent to the recording paper P. It is batch-transferred on the top.

  The recording paper P onto which the color image has been transferred is conveyed to the fixing device 9 while being guided by the conveyance guide plate. The color toner image on the recording paper P is heated and fixed by the fixing device 9. The recording paper P heated for melting the toner image is further pressure-cooled for image fixing, and then normally passes through the paper discharge path 61 and is sandwiched between the paper discharge rollers 51 and directly on the paper discharge tray 60. The paper is discharged.

  In the image forming apparatus 100 having the reverse paper discharge function and the double-sided image formation function, the recording paper P on which an image is formed on one side is once sent to the reverse conveyance path 50 by the paper discharge path switching plate 55. FIG. 2 is an enlarged schematic configuration diagram of the reverse conveyance path 50. 1 and 5 denote the same parts, and the configuration of the reverse conveyance path 50 of the recording paper P according to the present invention will be described below with reference to FIG.

  The reverse conveyance path 50 extends to the conveyance path 50A and the conveyance path 50A that are formed substantially vertically, separately from the normal paper discharge path 61, and is used for reversing the transfer paper during reverse paper discharge and double-sided image formation. It is composed of a conveyance path 50B and a conveyance path 50B for forming a double-sided image formed substantially horizontally by branching from the branch point 56. Further, the conveyance path 50A and the conveyance path 50C are provided with reverse conveyance roller pairs 52, 53, and 54 for conveying the recording paper P, respectively, and one of the roller pairs serves as a driving roller to the stepping motors 52a, 53a, and 54a. They are connected by rows or timing belts. A transport roller group 57 is also provided in the transport path 50B.

  The reverse conveyance roller pair 53 provided in the conveyance path 50C is a reverse conveyance roller pair positioned on the upstream side in the conveyance direction reversed at the time of reverse discharge, and is stepped on the recording paper P when the recording paper P is reversed. A configuration is provided in which the conveying force generated by driving the motor 53a is not transmitted (corresponding to the first aspect). Although all the embodiments are described as stepping motors, any one motor may be a stepping motor.

  As a method of canceling the conveyance of the recording paper P by driving the stepping motor, three specific methods are shown in the present invention. FIG. 3 shows a first configuration (configuration described in claim 2) by a method of releasing the pressure of the pair of reverse conveying rollers 53 using the cam 58. In this method, the cam 58 is provided coaxially with the drive roller 53b of the reverse conveyance roller pair 53 provided in the conveyance path 50C, and the cam 58 is rotated based on a control signal separately from the drive of the drive roller 53b.

  The side surface of the cam 58 is in contact with the driven roller 53c, and when the distance from the rotating shaft to the peripheral surface of the cam 58 is the shortest, the driving roller 53b and the driven roller 53c are pressed to sandwich the recording paper P. When the distance to the peripheral surface of the cam 58 becomes the maximum, the crimping is completely released.

  As a second configuration (a configuration described in claim 3), a configuration in which a clutch mechanism is provided although not shown is conceivable. Since this method is not a method of canceling the pressure bonding, the conveyance load of the recording paper P remains as compared with the pressure cancellation, but the load can be reduced. For example, the driving roller 53b of the reverse conveying roller pair 53 is coupled to the stepping motor 53a via a clutch mechanism. When it is necessary to convey the recording paper P by driving the stepping motor 53a of the reverse conveying roller pair 53, the clutch mechanism is kept connected, and when the conveying force by the stepping motor 53a is not transmitted to the recording paper P, the clutch is engaged. Control to cut.

  As a third configuration (configuration described in claim 4), the driving roller 53b of the reverse conveying roller pair 53 is directly connected to the stepping motor 53a via a gear train or the like. When the recording paper P needs to be conveyed by the stepping motor 53a of the reverse conveying roller pair 53, an excitation current is supplied to the rotor of the stepping motor 53a, and when the conveying force by the stepping motor 53a is not transmitted, the non-excited state is set. To control. Since the rotor of the stepping motor 53a has a small moment of inertia, the conveyance load when the recording paper P is pulled becomes small even if the reverse conveyance roller pair 53 holds the recording paper P.

  When forming an image on both sides of the recording paper P, the trailing edge of the recording paper P image-formed on one side passes through the conveyance path 50A and is conveyed to the conveyance path 50C and is sandwiched between the reverse conveyance roller pairs 53 and 54. To be stopped. Therefore, the reverse conveyance roller 54 provided in the conveyance path 50C is also a reverse conveyance roller pair positioned on the upstream side in the conveyance direction reversed during double-sided image formation. When the recording paper P is reversed, the same stepping as described above is performed. It is possible to provide a configuration that does not transmit the conveying force generated by driving the motor 53a (corresponding to the description of claim 1). However, since the reverse conveyance roller pair 53 itself has a conveyance force by the stepping motor 53a, the reverse conveyance roller pair 54 is not necessarily required.

  The control operation of the recording paper P at the time of reverse paper discharge and double-sided image formation of the reverse conveyance path 50 configured as described above will be described with reference to the flowchart of FIG. When reverse discharge is selected by the control unit of the image forming apparatus 100 by the control unit of the image forming apparatus 100 (S1), the recording paper P on which an image is formed on one side discharged from the fixing device 9 is discharged. It is guided by the path switching plate 55 and enters the conveyance path 50C, and is sandwiched by the pair of reverse conveyance rollers 52 of the conveyance path 50A and is conveyed downward along the conveyance path 50A (S2).

  The leading edge of the recording paper P is further sandwiched between a pair of reverse conveyance rollers 53 in the conveyance path 50C and guided to the lower part of the image forming apparatus 100. At this time, the reverse conveying roller pairs 52 and 53 are rotated at substantially the same linear speed by the stepping motors 52a and 53a so that the recording paper P is not pulled or pressed by the conveying of the reverse conveying roller pairs 52 and 53. .

  The rear end of the recording paper P in the conveyance direction (in this case, the normal rotation direction) passes through the paper discharge path switching plate 55 and enters the conveyance path 50C, and the recording paper P is held between both the reverse conveyance roller pairs 52 and 53. At this point, the driving of the stepping motors 52a and 53a is stopped, and the recording paper P is held while being sandwiched between the two reverse conveying roller pairs 52 and 53 (S3). At this time, the pair of rollers on the leading end side in the transport direction, that is, the reverse transport roller pair 53 is controlled slightly fast so that the recording paper P is not pulled.

  After that, the conveyance of the upstream roller in the reverse conveyance direction, that is, the reverse conveyance roller pair 53 by the driving of the stepping motor 53a is released (S4), and the downstream roller in the reverse conveyance direction, that is, the reverse conveyance roller pair 52 only. Reverse conveyance is started (S5).

  On the other hand, when the double-sided image formation is selected before the reverse paper discharge, the recording paper P on which the image is formed on one side discharged from the fixing device 9 is guided by the paper discharge path switching plate 55 to the transport path 50C. Then, the sheet is sandwiched between the reverse conveying roller pair 52 of the conveyance path 50A and conveyed downward in the conveyance path 50A (S6). The leading edge of the recording paper P is further sandwiched between the pair of reverse conveying rollers 53 in the conveying path 50C and guided to the lower part of the image forming apparatus 100 (S6).

  At the time of double-sided image formation, the rear end of the recording paper P in the transport direction (in this case, the forward rotation direction) passes through the branch point 56 and enters the transport path 50C. At this point, the driving of the stepping motors 53a and 54a is stopped, and the recording paper P is held in a state of being sandwiched between the two reverse conveying roller pairs 53 and 54 (S7). Thereafter, the conveyance of the upstream roller in the reverse conveyance direction, that is, the reverse conveyance roller pair 54 by the driving of the stepping motor 54a is released (S8), and only the downstream roller in the reverse conveyance direction, ie, the reverse conveyance roller pair 53 is used. Reverse conveyance is started (S5). As described above, the pair of reverse conveying rollers 54 for double-sided image need not be provided.

  As described above, in the optimal embodiment according to the present invention, the drive motors of the reverse conveying roller pairs 52, 53, 54 are described as the stepping motors 52a, 53a, 54a based on the fifth aspect. From the standpoint of preventing step-out and ensuring stable conveyance of the recording paper P, not all of them need to be stepping motors.

  For example, even if the driving motor of the reverse conveying roller pair 53 is a stepping motor 53a and the driving motor of the reverse conveying roller pair 52 is a DC motor, the stepping motor 53a of the reverse conveying roller pair 53 is released to release the conveying force. The problem of motor step-out is eliminated and the object of the present invention can be achieved. If the double-sided image formation and the reverse discharge are not selected, the recording paper P on which the image is formed on one side is discharged outside the apparatus through the normal discharge path 61 (S9).

  The case where there are two reverse conveying roller pairs has been described above. However, the present invention is not limited to two, and may be three or more. In the case of three or more, the object of the present invention can be achieved by releasing the conveyance by the motor drive of all the reverse conveyance roller pairs on the upstream side in the conveyance direction. A method of sequentially controlling the rotation of the motor as the recording paper P moves is also possible.

  The above-described configuration of the image forming apparatus is an embodiment, and the image forming apparatus 100 according to the present invention is not limited to this. Various changes can be made without departing from the gist of the present invention. Of course, it can be added.

1 is an overall configuration diagram of an image forming apparatus according to the present invention. It is the model block diagram which the reverse conveyance path expanded. It is explanatory drawing which shows the crimp release method of the reverse conveyance roller pair using a cam. 6 is a flowchart illustrating recording sheet control operations during reverse paper discharge and double-sided image formation. FIG. 6 is a functional explanatory diagram of a recording paper (transfer paper) reverse conveyance mechanism.

Explanation of symbols

1Y, 1M, 1C, 1K Photoconductor 7 Intermediate transfer body 8 Secondary transfer roller 9 Fixing device 20 Paper tray 25 Registration roller 50 Reverse conveyance path 51 Paper discharge rollers 52a, 53a, 54a Stepping motors 52, 53, 54 Reverse conveyance rollers Pair 55 Paper discharge path switching plate 58 Cam 61 Paper discharge path 100 Image forming apparatus P Recording paper (transfer paper)

Claims (5)

A plurality of reverse conveying roller pairs provided on the conveying path;
In the image forming apparatus in which each of the plurality of reverse conveying roller pairs is driven by a motor to convey transfer paper,
Among the motors, at least one motor is constituted by a stepping motor,
When the transfer sheet is nipped by each of the reverse conveyance roller pairs and stopped and then the conveyance direction is reversed, the reverse conveyance roller pair positioned on the upstream side of the reversed conveyance direction is driven by the motor. An image forming apparatus, wherein the stepping motor is prevented from being stepped out by releasing the conveyance.   The pair of reverse conveying rollers positioned on the upstream side in the reverse conveying direction includes a driving roller driven by the motor and a driven roller driven by the driving roller, and the transfer paper is reversely conveyed. When the conveyance direction is reversed after being sandwiched between the roller pairs and stopped, the reverse conveyance roller pair is conveyed by the motor drive by releasing the pressure-bonding state of the drive roller and the driven roller. The image forming apparatus according to claim 1, wherein the image forming apparatus is released.   The pair of reverse conveying rollers positioned on the upstream side in the reversed conveying direction includes a driving roller driven by the motor via a clutch mechanism and a driven roller driven by being driven by the driving roller, and the transfer roller When the conveyance direction is reversed after the paper is nipped and stopped by each of the reverse conveyance roller pair, the motor is driven by the reverse conveyance roller pair by releasing the connection of the clutch mechanism. The image forming apparatus according to claim 1, wherein the image forming apparatus is released.   The pair of reverse conveying rollers located on the upstream side in the reverse conveying direction includes a driving roller driven by the stepping motor and a driven roller driven by the driving roller and the transfer paper is reversed. When the conveyance direction is reversed after being sandwiched between the conveyance roller pairs and stopped, the conveyance of the reverse conveyance roller pair by the motor drive is canceled by cutting off the excitation of the stepping motor. The image forming apparatus according to claim 1, wherein:   The image forming apparatus according to claim 1, wherein all of the motors are stepping motors.

Images