JP2006182475A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device having a simple configuration and capable of improving productivity in image formation. <P>SOLUTION: This image forming device having an electrophotograpic system has a detection sensor provided on the downstream side of a fixation means, an inversion delivery roller provided at a downstream side position of the detection sensor, a transfer material introducing conveyance passage and a transfer material inversion discharge passage provided on the upstream side of the inversion delivery roller, and a control means for controlling speed and direction of rotation of the inversion delivery roller. The control means decides timing for allowing a rear end of a transfer material to pass a nip part of the fixation means when the detection sensor detects a tip of the transfer material, increases speed of the inversion delivery roller at the timing, feeds the transfer material into the transfer material inversion discharge passage by rotating the inversion delivery roller by increasing speed by directing the direction of its rotation into the reverse direction after a predetermined time, and then directing the direction of rotation of the inversion delivery roller into the reverse direction again to reduce speed to initial speed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that creates an image using an electrophotographic system such as a copying machine or a printer.

  An image carrier such as a drum-shaped photoconductor is charged and exposed to form an electrostatic charge latent image corresponding to the document or the image signal, and the latent image is visualized by a contact or non-contact development method (toner image). Then, after the toner image is transferred onto a transfer material such as paper, the toner image is fixed on the transfer material by a fixing device having heating / pressurizing means and discharged outside the apparatus. Image forming apparatuses are well known.

  Further, in the image forming apparatus as described above, when the transfer material is discharged out of the apparatus, there is a configuration in which the transfer material is discharged after being turned upside down.

  For example, an image is formed on one side, the front and back sides of the transfer material conveyed inside the machine are reversed with the image side up, and the non-image side (blank surface) is placed on the tray provided outside the machine. That is the structure that discharges.

  Such reverse paper discharge enables, for example, page alignment of transfer materials when a single-sided original is recorded sequentially from the first page.

  The same applies to the transfer material recorded in the double-sided recording mode.

  On the other hand, an image forming apparatus is desired to increase the capacity of the number of image forming sheets that can be recorded per unit time. In such a case, the mode of discharging the transfer material after reversing the transfer material as described above is disadvantageous. It becomes a condition.

As a method for increasing the production capacity of the number of image formations in the image forming apparatus, for example, two sensors for detecting a transfer material are provided on a paper conveyance path between a fixing roller and a paper discharge roller, and either one of them is provided. After the sensor detects the trailing edge of the transfer material, the linear speed of the discharge roller is made faster than the linear speed of the fixing roller at a predetermined timing, and the time for the transfer material to pass through the double-sided paper refeed path Has been proposed (see, for example, Patent Document 1).
JP 2003-182907 A

  However, the configuration disclosed in Patent Document 1 has a configuration in which a driven roller that follows the paper discharge roller is provided above and below the paper discharge roller, and a switching claw is provided on the front side of the roller. Then, the transfer claw is switched by the switching claw, and the transfer material on which the image is formed is discharged to the tray outside the apparatus by the discharge roller and one driven roller, and the transfer material on which the image is formed on one side is discharged. The sheet is received by the sheet discharge roller and the other driven roller, and after a predetermined time, the sheet discharge roller is rotated in reverse at an increased speed to reversely discharge the transfer material to the double-sided refeed path for double-sided image formation.

  Thus, since one paper discharge roller, two driven rollers, and the switching claw are controlled, the mechanical configuration and control are complicated.

  In addition, since the acceleration timing for discharging the transfer material to the double-sided paper re-feed path is a predetermined time after the sensor detects the trailing edge of the transfer material, it is difficult to say that productivity is sufficient.

  Further, increasing the speed increase is not preferable because noise increases.

  The present invention has been made in view of the above-described problems, and a main object thereof is to provide an image forming apparatus having a simple configuration and improved image forming productivity.

The object of the present invention can be achieved by the following constituent elements.
(Claim 1) A toner image formed on an image carrier by electrophotography is transferred onto a transfer material, and the transfer material is passed through a fixing device having a heating / pressurizing unit to transfer the toner image to the transfer material. In the image forming apparatus configured to discharge the transfer material from the reversing unit after reversing the front and back of the transfer material by the reversing unit,
A transfer material detection sensor provided at a downstream position of the heating / pressurizing means when viewed in the transfer material conveyance direction, and a reversible reversal discharge roller provided at a downstream position of the transfer material detection sensor. And a transfer material introduction conveyance path and a transfer material reverse discharge path provided on the upstream side of the reverse discharge roller, and a control means for controlling the speed and rotation direction of the reverse discharge roller,
The control means determines the timing at which the trailing edge of the transfer material passes through the nip portion of the heating / pressurizing means based on detection of the leading edge of the transfer material by the transfer material detection sensor, and transfers at the timing. The reverse discharge roller that is transporting the material is rotated at an increased speed, and after a predetermined time, the reverse discharge roller is driven in the reverse direction and rotated at a higher speed to transport the transfer material introduction transport path. An image forming apparatus, wherein the transferred transfer material is sent to a transfer material reversal discharge path.
(Claim 2) The timing at which the trailing edge of the transfer material passes through the nip portion of the heating / pressurizing means is determined based on information of a size detecting means provided in relation to a paper feed tray. The image forming apparatus according to claim 1.
(Claim 3) The timing at which the rear end of the transfer material passes through the nip portion of the heating / pressurizing unit is provided at a position upstream from the heating / pressurizing unit as viewed in the conveying direction of the transfer material. The image forming apparatus according to claim 1, wherein the image forming apparatus is determined based on a transit time passing over another sensor.

  According to the first aspect of the present invention, when the transfer material detection sensor provided on the outlet side of the fixing device detects the leading edge of the transfer material, the control means causes the trailing edge of the transfer material to cover the nip portion of the heating / pressurizing means. Determine the timing to pass, and rotate the reverse paper discharge roller that is transporting the transfer material at that speed, and after a predetermined time, rotate the reverse paper discharge roller in the reverse direction and rotate it at a higher speed. The transfer material that has been conveyed through the transfer material introduction conveyance path is sent to the transfer material reversal discharge path, and the rotation direction of the reverse discharge roller at the timing when the rear end of the transfer material leaves the reverse discharge roller. The image forming productivity is improved as much as possible by making the image in the reverse direction again and decelerating to the initial speed so that the next transfer material can be immediately taken in and repeatedly discharged in the same manner as described above. This Can.

  In the invention according to claim 2, since the size information of the transfer material to be used can be determined with sufficient time, it is possible to control with high accuracy.

  Furthermore, the invention according to claim 3 can improve the control accuracy in the same manner as the invention according to claim 2.

  An example of an embodiment according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic diagram showing a configuration of an image forming apparatus including a digital copying machine.

  The image forming apparatus of the present embodiment forms a toner image formed on an image carrier using an electrophotographic system on a transfer material such as plain paper, and includes an automatic document feeder 1 and an image reader 2. , An image forming unit 3, a transfer material storage unit 4, a paper feed unit 5, a reverse paper discharge / refeed unit 6, and a reverse conveyance unit 8.

  The automatic document feeder 1 includes a document placing table 11 on which a document is placed, a document separating unit 12 that separates a document placed on the document placing table 11, and a plurality of documents that are transported by the document separating unit 12. A document conveying means 13 including a plurality of rollers, a document discharging means 14 for discharging a document conveyed by the document conveying means 13, a document discharging table 15 for placing a document discharged by the document discharging means 14, and The document reversing unit 16 includes a pair of rollers for reversing the front and back of the document in the duplex copying mode.

  Reference numeral 100 in the upper part of the apparatus body denotes an operation unit, 110 denotes a start button for starting image formation, and 120 denotes a power switch.

  A plurality of documents (not shown) placed on the document placing table 11 are separated one by one by the document separating means 12 and conveyed toward the image reading position by the document conveying means 13.

  The original reading position is provided below the original conveying means 13 so that the original image can be read through the slit 21 of the image reading apparatus 2.

  On the other hand, when reading images on both sides of the document, the document once read on one side is guided to the document reversing means 16, and the rear end of the document is sandwiched between a pair of reversing rollers constituting the document reversing means 16. In this state, the pair of reversing rollers is stopped, rotated reversely to reverse the front and back of the document, and transported again by the document transporting unit 13, so that the image on the other surface (second surface) is captured at the document reading position. Can be read.

  The automatic document feeder 1 is configured to be retractable. The automatic document feeder 1 is raised to open the platen glass 22 and place the document directly on the platen glass 22 for copying. It is configured so that it can be performed.

  The image reading device 2 is a device for reading an image of a document to obtain image data, and integrally includes a lamp 231 that irradiates the document through the slit 21 and a first mirror 232 that reflects reflected light from the document. The second mirror unit 24 formed by integrating the first mirror unit 23, the second mirror 241 that reflects the light from the first mirror 232, and the third mirror 242, and the second mirror unit 24. An image forming lens 25 that forms an image of the reflected light on a CCD, which is an image sensor, and a linear CCD 26 that photoelectrically converts the light image formed by the image forming lens 25.

  The photoelectrically converted analog signal is A / D converted after analog processing, subjected to appropriate image processing, and then stored in a memory in the control means C as image data.

  The control means C comprises a CPU and controls the entire apparatus by multitasking.

  In other words, the energization control of the heating source of the fixing device is performed by the ON signal input of the power switch 120 provided in the main body of the apparatus, and each related unit is driven and controlled according to the program flow for the initialization of the apparatus. .

  In addition, after the initialization of the apparatus is completed, the idling state is maintained, and the operation corresponding to the selected image forming mode is executed via the drive control of each driving unit according to the pressing of the start button 110 for image formation. Let

  In the aspect in which the image reading device 2 reads the document fed by the automatic document feeder 1, the first mirror unit 23 and the second mirror unit 24 are fixed at the illustrated positions.

  The reading of the image of the document placed on the platen glass 22 is performed by moving the first mirror unit 23 and the second mirror unit 24 along the platen glass 22 while maintaining the optical path length. To do.

  The image forming unit 3 includes a photosensitive drum 31 having a photoconductive photosensitive layer as an image carrier on its surface, and charging means (hereinafter referred to as a charger) including a charging electrode for uniformly charging the surface of the photosensitive drum 31. 32. Laser writing means 33 which is operated based on the image data after the image processing and exposes the photosensitive drum 31 to form an electrostatic charge latent image, on the photosensitive drum 31. A developing unit (hereinafter referred to as a developing device) 34 having a roller-shaped developer carrier (hereinafter referred to as a developing sleeve) 300 that reversely develops the formed electrostatic charge latent image to form a toner image, and the toner image is converted to plain paper. For example, AC or AC and DC are transferred from a transfer means (hereinafter referred to as a transfer device) 35 including a transfer electrode that is transferred onto a transfer material (hereinafter referred to as paper) made of A cleaning unit including a separating unit 36 that performs corona discharge by the folded voltage and promotes separation of the sheet from the photosensitive drum 31, and a blade for cleaning the photosensitive drum 31 after the transfer process is completed. 37 etc.

  In the present embodiment, the photosensitive drum 31, the developing device 34, and the cleaning unit 37 are configured as a process cartridge 3A.

  In the present embodiment, the charging electrode, the transfer electrode, and the separation electrode of the separation means are made of an oxide-coated tungsten wire, and the developer housed in the developing unit 34 is particulate ferrite and styrene acrylic resin. And a two-component developer mainly composed of a so-called coating carrier and a polymerized toner produced by a polymerization method.

  Reference numeral 38 denotes a conveying belt that conveys the separated paper toward a fixing device, for example, a heating roller type fixing device 9, and 63 denotes a paper discharge roller.

  The fixing device 9 has a built-in heating source H, an upper fixing roller (heating roller; heating means) 900 that rotates independently around it, and a lower fixing roller (pressure roller) that rotates while being in pressure contact with the upper fixing roller 900. A pressurizing unit) 903 as a main component, and a fixing discharge roller 61, a switching unit 62 for selectively switching a paper transport path, and the like are integrally provided.

  Reference numeral W denotes a cleaning web, a part of which is provided in contact with the surface of the fixing upper roller 900, and is wound little by little on the winding core shown on the left side of the drawing at an appropriate time interval during operation of the apparatus, for example. It has come to be taken.

  In the image formation with the above configuration, the photosensitive drum 31 rotated in the direction of the arrow by an appropriate driving unit is sequentially charged by the charger 32, and then the electrostatic charge latent corresponding to the original image is formed by dot exposure by the laser writing unit 33. An image is formed, and the electrostatic latent image is formed into a toner image by contact development or non-contact development using the developing device 34, and then fed by the rotation of the registration roller 56 as the second paper feeding means. In addition, the transfer is achieved through the operation of the transfer unit 35.

  Actually, a process for forming a toner image on the photosensitive drum 31 in synchronization with the paper feeding accompanying the start of rotation of the registration roller 56 in a state where the paper has reached the registration roller 56. Is supposed to start.

  The sheet after the transfer is separated from the photosensitive drum 31 by the action of the separating means 36, and after being subjected to the heating / pressurizing action of the fixing device 9, it is discharged out of the apparatus.

  On the other hand, the photosensitive drum 31 that has passed through the transfer region continues to rotate, the residual toner is removed by the blades that constitute the cleaning unit 37, and preparation for the next image formation is made.

  Returning to the description of the configuration, in the paper storage unit 4, paper feed trays 400, 410, and 420 for storing the paper P in a stacked state are arranged in the vertical direction (the paper P is shown only in the paper feed tray 400). Each of the paper feed trays includes paper feed rollers 401, 411, and 421 and a pair of separation rollers 403, 413, and 423.

  The paper feed unit 5 includes a transport roller pair (hereinafter also referred to as a transport roller) R1 as transport means for transporting the paper P from each of the paper feed trays 400, 410, 420 to the image forming unit 3. R2, R3, R4, R5 and R6 are provided.

  55 is a transport roller provided downstream of the transport roller R6 in the transport direction of the paper P, a transport path of the paper sent out through the reverse transport unit 8, and a paper fed from the paper feed tray 400, for example. Is provided at the junction with the transport path.

  The reverse discharge / refeed unit 6 is an area for reversely discharging and transferring the paper P after transfer / fixing, or for refeeding the paper P in accordance with the double-sided image forming mode. When the discharged paper P is discharged out of the machine as it is, when it is discharged after being turned upside down, and to form an image on the back surface (second surface) of the paper P, the paper P is directed toward the registration roller 56. There is switching means 62 (existing) for switching the conveyance path in the case of refeeding.

  When the image-formed paper P is discharged as it is, that is, with the transferred image surface facing upward, the switching means 62 is held at the position indicated by the alternate long and short dash line in the figure, and the image-formed paper When discharging the paper with its front and back reversed, the switching means 62 is held at the position indicated by the solid line in the drawing, and the paper P conveyed by the fixing and discharging roller 61 is paired with the reverse discharging roller 600 and the conveying roller. 610 is fed into the transfer material introduction conveyance path, and the operation of the roller group is stopped at a timing when the rear end reaches a position in front of the reverse discharge roller 600, and then the reverse discharge roller 600. The transfer material is formed on the left side of the switching means 62 by reversibly controlling the rotation direction of the drive motor (not shown) so that the rotation direction of the drive motor is rotated in the opposite direction. Rolling feed to the discharge path, through a discharge roller 63 and discharged to the outside of the discharge tray 64.

  Further, in the double-sided image forming mode in which an image is formed on the second side of the paper P following the first side, the paper transported by the fixing discharge roller 61 while holding the switching means 62 at the position indicated by the solid line in the drawing. Is fed to the reverse conveyance unit 8 via the reverse discharge roller 600 and the conveyance roller 610 of the reverse discharge / refeed unit 6 driven by the discharge motor, and the reverse conveyance unit 8 reverses the front and back of the paper P. Then, it is sent out toward the registration roller 56.

  The process until the transfer image is obtained on the second surface of the paper P is the same as described above, and the paper P after the fixing process is discharged according to any one of the forms described above.

  The roller pairs 803, 805, 807, 809, 811 including the conveyance roller pair 800 are conveyance rollers provided on the conveyance path of the reverse conveyance unit 8.

  In the figure, reference numeral S shown in the fixing device 9 as viewed in the transport direction of the paper P, in other words, the downstream position of the heating / pressurizing means, is a transfer material detection sensor (hereinafter referred to as paper detection) comprising a photo interrupter. Sensor).

  In the present embodiment, the paper detection sensor S detects the leading edge of the paper after passing through the fixing device, and the detection information is taken into the control means C and used for controlling the reverse paper discharge roller 600. Is done.

  That is, in the reverse paper discharge mode, when the leading edge of the paper P after passing through the fixing device 9 is detected by the paper detection sensor S, the trailing edge of the paper P is moved to the fixing device 9 (specifically, based on the information). In this case, the time until it passes through the nip portion of the heating / pressure roller is determined by calculation by the calculation means in the control means S.

  The fixing device passage time of the paper P can be obtained, for example, by providing a size detection sensor on the paper feed tray side, capturing the paper size information in the transport direction by the sensor, and dividing the size by the process linear velocity. it can.

  At that time, the paper length from the nip portion of the heating / pressurizing means to the paper detection sensor S or the time corresponding to the paper is corrected as appropriate during the calculation.

  Then, after a predetermined time according to the calculation, the reverse discharge roller 600 is driven at a linear velocity higher than the process linear velocity (for example, the linear velocity of the photosensitive drum).

  Further, the roller P is stopped at the timing when the rear end portion of the paper P is nipped by the reverse paper discharge roller 600, and then the reverse paper discharge roller is rotated in the reverse direction and at the same linear velocity increased as described above. This time, P is discharged from the inversion area with the trailing edge as the head.

  When the trailing edge (leading edge at the time of introduction) of the paper P passes through the nip portion of the reverse paper discharge roller, the reverse paper discharge roller 600 is stopped and continuously rotated at the same linear speed as the process speed, and the subsequent second The preparation for transporting the paper P is completed. Then, the above process is repeated as many times as necessary.

  When there is a state in which the paper P is sandwiched by the fixing discharge roller 61, the reverse paper discharge roller 600, and the transport roller 610 at the time when the reverse paper discharge roller is accelerated, the paper P is placed on the downstream transport roller. It is comprised so that an excessive pushing state may not be generated.

  The fixing discharge roller 61 is connected to a one-way clutch that idles when the paper P is pulled by the roller 600, and the reverse discharge roller 600 and the transport roller 610 are driven by the same driving means and rotate at the same outer peripheral speed. Even when the reverse discharge roller 600 is accelerated, the fixing discharge roller 61 and the roller 600 can be pulled by the roller 600, and the reverse discharge roller 600 and the conveyance roller 610 can have the same speed. The upstream roller is configured not to cause the paper P to be pushed in with respect to the downstream conveying roller.

  With the above configuration, the tension of the sheet by the reverse discharge roller 600 can be reduced, and the conveyance roller 610 can be driven at a linear velocity corresponding to the process linear velocity and the linear velocity when increased.

  Next, a second embodiment of the reverse sheet discharge according to the present invention will be described. The configuration of the image forming apparatus is basically the same as that of the image forming apparatus shown in FIG. Therefore, the configuration of the image forming apparatus shown in FIG. 1 will be described as needed as appropriate.

  FIG. 2 is a diagram for explaining the control of the reverse paper discharge roller and the behavior of the paper P in the reverse paper discharge / refeed unit 6, and shows an enlarged schematic view of the portions necessary for the description.

  In FIG. 2, the same members (means) as those shown in FIG. 1 are denoted by the same reference numerals, and redundant description will be avoided as much as possible.

  In the figure, S1 shown at the downstream position of the registration roller 56 when viewed in the paper transport direction is a paper length detection sensor that detects the length of the paper P in the transport direction.

  The time from when the paper length detection sensor S1 detects the leading edge of the paper (ON state) until the trailing edge of the paper is detected (OFF state) is counted by a timer provided in the control means C, and will be described later. Used for timing setting of paper roller 600 speed control.

  The switching means 62 positioned downstream of the fixing device is configured to reversely discharge the paper P, and detects the leading edge of the paper P that is sent toward the transfer material introduction conveyance path (without reference numeral) after passing through the fixing device. A sheet detection sensor S made of a photo interrupter is provided in the vicinity of the fixing device outlet side and at a position facing the switching means 62.

  Below the switching means 62, a reverse discharge roller 600 is installed. The paper P is sent out substantially vertically downward, the driving is stopped in a state where the rear end portion of the paper is held, and the reverse rotation driving control immediately after is received. The sheet is sent out from the reversal area toward the transfer material reversal discharge path, and is discharged via a paper discharge roller 63 to a tray provided outside the apparatus.

  In the above, the time information T counted and stored by the timer according to the paper detection of the paper length detection sensor S1 is used when the paper detection sensor S detects the leading edge of the paper.

  That is, when the paper detection sensor S detects the leading edge of the paper P, the count of the acceleration start timer is started. When the count becomes equal to the time information T, the reverse discharge roller 600 is detected from the process linear velocity. Is also driven at a high linear velocity and transports the paper P.

  This timing is the timing when the trailing edge of the paper P finishes passing through the nip portion of the heating / pressurizing means in the fixing device 9, and the timing when the leading edge of the paper is already nipped by the reverse paper discharge roller.

  As a result, the paper P is rapidly drawn by the reverse paper discharge roller, and moves on the transfer material introduction conveyance path.

  After that, the reverse paper discharge roller is stopped driving with the rear end of the paper P being sandwiched, and immediately after that, the reverse paper is rotated in the speed-up state, and the drawn paper P is moved to the front of the reverse paper discharge roller. Starting from the area (reversal area), the sheet is fed to the transfer material reversal carry-out path formed on the left side of the switching means 62.

  Immediately after the leading edge of the paper passes through the reverse paper discharge roller, the drive of the reverse paper discharge roller is controlled to stop, and then it is driven back to the normal rotation and the process linear velocity again to prepare for receiving the subsequent paper. Is done.

  Note that the time information T stored in the control means C is appropriately cleared and prepared for acquisition of time information of the next sheet.

  As apparent from the above, the conveyance control is performed in such a manner that the trailing edge of the first sheet P1 and the leading edge of the subsequent second sheet P2 are switched directly above the reverse discharge roller.

  As in the first embodiment, the driving source for driving the reverse discharge roller 600 in this embodiment is a stepping motor, but other types of motors are used as long as the intended purpose can be achieved. can do.

  For example, the reverse discharge roller 600 is controlled to stop rotation, reverse rotation, and forward rotation again. For example, a sensor is provided above and downstream of the reverse discharge roller, and the leading or trailing edge of the sheet is detected by the sensor. The detection information can be taken into the control means C, and the time information T described above can be used for control.

  FIG. 3 is a control flow that shows simplified control up to acceleration of the reverse paper discharge roller.

  This control flow is shown including the first embodiment.

  That is, information relating to the length of the paper in the conveyance direction or the passage time information T from the leading edge to the trailing edge of the paper is controlled by a sensor provided on the paper feed tray side in step 1 or a sensor provided on the conveyance path. C is taken in.

  The information on the length of the paper in the conveyance direction is calculated by the control means C, and the time (time information T) required to pass one point from the leading edge to the trailing edge of the paper is determined.

  When the sheet is detected by the sheet detection sensor S provided on the exit side of the fixing device 9, the acceleration start timer starts counting (step 3), and the reverse discharge roller 600 is accelerated.

  Subsequently, the reverse discharge roller 600 is accelerated with the passage of a predetermined time (step 4) in which the count coincides with the already acquired time information T (step 5).

  The subsequent control of the reverse paper discharge roller has already been described in detail and will be omitted.

  As described above, the configuration according to the first and second embodiments is the control method in the conventional apparatus, that is, the method of increasing the speed of the reversing roller after a predetermined time after detecting the trailing edge of the paper that has passed through the fixing device. As compared with the above, the accuracy can be increased and the productivity can be increased.

  Next, the productivity will be described briefly.

  The sheet detection sensor provided on the fixing exit side is installed at a location about 70 mm away from the member in order to protect the member from the influence of high temperature.

  Now, it is assumed that the reverse discharge roller is accelerated after the sheet detection sensor is turned off (68 mm after the sheet passes through the nip portion of the fixing device), and 75 PPM (75 sheets in length in the conveying direction) is A4 laterally fed. (Recording / minute), the process linear velocity is 357 mm / second.

  In this case, the distance between the leading edge of the preceding sheet and the leading edge of the succeeding sheet before entering the fixing device is 286 mm, and the distance between the trailing edge of the preceding sheet and the leading edge of the succeeding sheet is 76 mm.

  The reversal margin in the reversal discharge section must be taken by the time spent for the conveyance for 76 mm, while the reverse discharge roller is accelerated, stopped, reverse speed increased, stopped, and low speed (stepping motor). 159 msec is required to perform a series of controls of (process speed) forward rotation.

  Here, the reversal margin is the minimum from the end of the preceding paper discharge (accelerated state) operation by the reverse discharge roller to the completion of the subsequent paper receiving preparation (normal rotation low speed state after stop). Say the required time (msec).

  In order to create this reversal margin 159 msec, the reversal discharge roller is accelerated, and in the above, the linear velocity is 700 mm / sec.

  However, as related to the present invention, a sheet detection sensor is provided at the same condition position of the fixing exit, and after the sensor detects the leading edge of the sheet, the same line as described above at the timing when the trailing edge of the sheet passes 20 mm through the nip portion. If conveyance control is performed at a speed of 700 mm / sec, the reversal margin can be increased to 204 msec.

  If this 204 msec is matched with the above-described reversal margin of 159 msec using the conventional apparatus as an example, the distance between sheets (the distance between the trailing edge of the preceding sheet and the leading edge of the succeeding sheet) can be reduced to 58 mm. As a result, 80 PPM can be achieved without increasing the speed, and productivity can be improved.

1 is a schematic diagram illustrating a configuration of an image forming apparatus including a digital copying machine. FIG. 6 is a diagram for explaining the control of a reverse discharge roller and the behavior of a sheet in a reverse discharge / refeed unit. It is a control flow that shows simplified control up to acceleration of the reverse paper discharge roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Automatic document feeder 2 Image reading device 3 Image forming part 4 Transfer material storage part 5 Paper feed part 6 Reverse discharge / refeed part 600 Reverse discharge roller 8 Reverse conveyance part 9 Fixing device S Transfer material detection sensor ( Paper detection sensor)

Claims (3)

The toner image formed on the image carrier by electrophotography is transferred onto a transfer material, and the transfer material is fixed to the transfer material by passing through a fixing device having heating / pressurizing means. In the image forming apparatus configured to discharge the transfer material from the reversing unit after reversing the front and back of the transfer material by means,
A transfer material detection sensor provided at a downstream position of the heating / pressurizing means when viewed in the transfer material conveyance direction, and a reversible reversal discharge roller provided at a downstream position of the transfer material detection sensor. And a transfer material introduction conveyance path and a transfer material reverse discharge path provided on the upstream side of the reverse discharge roller, and a control means for controlling the speed and rotation direction of the reverse discharge roller,
The control means determines the timing at which the trailing edge of the transfer material passes through the nip portion of the heating / pressurizing means based on detection of the leading edge of the transfer material by the transfer material detection sensor, and transfers at the timing. The reverse discharge roller that is transporting the material is rotated at an increased speed, and after a predetermined time, the reverse discharge roller is driven in the reverse direction and rotated at a higher speed to transport the transfer material introduction transport path. An image forming apparatus, wherein the transferred transfer material is sent to a transfer material reversal discharge path. The timing at which the rear end of the transfer material passes through the nip portion of the heating / pressurizing unit is determined based on information of a size detecting unit provided in relation to the paper feed tray. The image forming apparatus described. The timing at which the rear end of the transfer material passes through the nip portion of the heating / pressurizing means is on the other sensor provided upstream of the heating / pressurizing means, as viewed in the transfer direction of the transfer material. The image forming apparatus according to claim 1, wherein the image forming apparatus is determined based on a passing time.

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