JP2007310305A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus suppressing deterioration in productivity when an image is formed on both sides of paper. <P>SOLUTION: The image forming apparatus 1 is provided with: an image forming mechanism 10 forming the image on the paper; a paper transporting mechanism 20 with a paper tray 24a and transporting the paper; and a paper resupplying transporting mechanism 30 transporting the paper to the paper transporting mechanism 20 by reversing front and back of the paper to form images on both sides of the paper. The paper transporting mechanism 20 is provided with a first paper position correcting mechanism 25 correcting the position of the paper by having the paper abutted to a registration roll 256 and forming a loop. The paper resupplying transporting mechanism 30 is provided with a second paper position correcting mechanism 33 correcting the position of the paper by having the paper abutted to a resupplied paper standby roll 331 and forming a loop. The first paper position correcting mechanism 25 varies the amount of the formed loop in the paper according to whether the paper is transported from the paper tray 24a or the resupplying paper transporting mechanism 30. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet.

Conventionally, an image forming unit, a sheet conveying unit that conveys a sheet via the image forming unit, and a refeed conveying unit that inverts the sheet on which an image is formed by the image forming unit and conveys the sheet to the sheet conveying unit. An image forming apparatus that forms images on both sides of a sheet is known as a copying machine, a printer, or a facsimile. In this image forming apparatus, a sheet on which an image is formed by transferring and fixing a toner image in the image forming apparatus is turned upside down by the refeed conveyance section and conveyed again to the sheet. An image is formed on the rear surface after being conveyed to the conveyance unit. In such a sheet conveying unit of the image forming apparatus, normally, in order to match the timing at which the sheet is fed to the image forming unit with the timing at which the toner image is formed in the image forming unit, the sheet conveyance is temporarily stopped and then conveyed. A pair of registration rolls is provided. Further, when the sheet is abutted against the registration roll, a loop is formed on the sheet, and the skew state of the sheet is also corrected. Here, in Patent Document 1, in order to correct the skew state by using the time to wait until the paper that has been turned upside down is sent back to the paper transport unit, the skew feeding state is also applied to the refeed transport unit. An image forming apparatus having a pre-registration roll for correction is disclosed.
JP 2000-153967 A

  However, in an image forming apparatus that forms an image on both sides of a sheet, the timing at which a sheet that has been turned upside down is sent again to the image forming unit by the sheet conveying unit is always relative to the timing at which the toner image is formed in the image forming unit. It is not always possible to afford. For example, when a sheet on which an image is formed on the back side comes into contact with an obstacle and conveyance is delayed, the sheet is jammed if the timing at which the toner image is transferred by the image forming unit is not in time. In order to avoid paper jamming, the timing of forming the transferred toner image is delayed on the image forming unit side. However, when the image forming unit forms an image on a plurality of papers, Since the front surface and the back surface are alternately processed at regular intervals, the timing of image formation needs to be greatly shifted in order to adjust the timing, which reduces productivity.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an image forming apparatus in which paper jam is unlikely to occur and an increase in productivity is suppressed when images are formed on both sides of a paper.

The image forming apparatus of the present invention that achieves the above object provides:
An image forming unit that forms an image on the conveyed paper;
A paper storage unit that stores a paper on which an image is formed in the image forming unit, and that transports the paper on a paper transport path passing through the image forming unit;
In order to form the image on both sides of the sheet again by conveying the sheet on which the image is formed in the image forming unit to the sheet conveying unit again, the sheet is reversed and conveyed to the sheet conveying unit. With
The paper transport unit has a pair of first rolls that come into contact with each other, and a paper is abutted against the first roll to form a loop, whereby a first paper posture correction is performed to correct the posture of the paper. Part
The re-feed conveyance unit has a pair of second rolls that come into contact with each other, and a second paper that corrects the posture of the paper by the paper being abutted against the second roll to form a loop. Equipped with a posture correction unit,
The first paper attitude correction unit changes an amount of forming a loop on the paper depending on whether the paper is transported from the paper storage unit or the re-feed transport unit. It is characterized by that.

  In the image forming apparatus of the present invention, in order to form an image on both sides, the paper that has been turned upside down by the refeed conveyance unit is corrected in posture by the second paper posture correction unit and conveyed to the paper conveyance unit. Therefore, the first paper posture correction unit of the paper transport unit changes the amount of loop formation depending on whether the paper posture is uncorrected or has been corrected once, so that the paper is fed to the image forming unit. It is possible to adjust the time until the feeding. Therefore, it is possible to suppress the occurrence of a paper jam due to a delay in the paper conveyance timing and a decrease in productivity.

Here, in the image forming apparatus according to the present invention, the re-feed conveyance unit has a sheet upstream of the second roll in a re-feed conveyance direction in which the sheet is conveyed toward the sheet conveyance unit. A first paper detection unit for detecting the presence or absence of
It is preferable that the second paper attitude correction unit changes an amount of forming a loop on the paper according to a timing at which the first paper detection unit detects the paper.

  The paper on which the image is formed on one side by the image forming unit is turned upside down by the refeed conveyance unit and conveyed to the paper conveyance unit, but may wait until it is conveyed to the paper conveyance unit. In some cases, it is transported with a delay while it is transported. For example, when the sheet is conveyed with a delay at a position upstream of the second roll in the refeed conveyance direction, the amount of loop formation by the second sheet attitude correction unit is reduced, and the sheet is quickly By conveying to the conveyance unit, it is possible to further reduce the occurrence of problems due to the delay in conveyance of the paper.

In the image forming apparatus according to the aspect of the invention, the re-feed conveyance unit may be configured such that the sheet re-feed unit is disposed upstream of the second roll in the re-feed conveyance direction in which the sheet is conveyed toward the sheet conveyance unit. A first paper detection unit for detecting presence or absence;
The second paper attitude correction unit may omit the formation of a loop and pass the paper when the first paper detection unit detects the paper after a predetermined timing has elapsed. Good.

In the image forming apparatus according to the aspect of the invention, the re-feed conveyance unit may be configured such that the sheet is disposed downstream of the second roll in the re-feed conveyance direction in which the sheet is conveyed toward the sheet conveyance unit. A second paper detection unit for detecting presence or absence;
Preferably, the first paper attitude correction unit changes an amount of forming a loop on the paper according to a timing at which the second paper detection unit detects the paper.

  The first paper posture correction unit can cope with the timing of the paper carried out from the second roll of the second paper posture correction unit, which is the previous stage.

  Further, in the image forming apparatus of the present invention, the first paper attitude correction unit is configured to form a loop on the paper conveyed from the refeed conveyance unit, and the amount of paper conveyed from the paper storage unit. It is preferable that the amount is smaller than the amount of loop formation.

  By reducing the loop formation amount of the sheet conveyed from the refeed conveyance unit, it is possible to shorten the time for forming an image on the back side surface of the sheet, thereby improving productivity.

  Further, the image forming apparatus of the present invention has a first loop that causes the first paper posture correction unit to form a paper loop even when the second paper posture correction unit forms a paper loop. When the second paper orientation correction unit forms a loop on the paper, the first paper orientation correction unit omits the formation of the paper loop and passes the paper. It is preferable that a correction mode switching unit that switches between two correction modes is provided.

  Since it is possible to switch between the first correction mode and the second correction mode, it is possible to correct an appropriate posture according to the required productivity.

  In the image forming apparatus of the present invention, the second paper attitude correction unit includes a guide member made of an elastic member that suppresses a loop formed on the paper abutted against the second roll. Alternatively, the sheet may be provided with a baffle chute urged by an elastic member that is curved and guided to the second roll.

  As described above, according to the present invention, when an image is formed on both sides of a sheet, it is possible to suppress the occurrence of a sheet jam or a decrease in productivity due to a delay in sheet conveyance timing.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the first embodiment of the present invention.

  An image forming apparatus 1 shown in FIG. 1 forms an electrostatic latent image, develops it with toner, forms a toner image, and finally transfers and fixes the toner image on a sheet, thereby fixing toner on the sheet. An image forming apparatus that forms an image composed of an image. The image forming apparatus 1 includes an image forming mechanism 10, a paper transport mechanism 20, a refeed transport mechanism 30, a control unit 40, and a touch panel 50.

  The image forming mechanism 10 is a mechanism for forming an image on the conveyed paper. The image forming unit 10Y corresponds to each color of yellow (Y), magenta (M), cyan (C), and black (K). The image forming apparatus 1 including 10M, 10C, and 10K is a tandem type printer in which the image forming units 10Y, 10M, 10C, and 10K are arranged in parallel, and can print a monochrome image. In addition, a full color image composed of four color toner images can be printed. These four image forming units 10Y, 10M, 10C, and 10K have substantially the same configuration, and the image forming unit 10Y corresponding to yellow will be described as a representative example. A photoconductor 11Y, a charger 12Y, an exposure device 13Y, a developing device 14Y, a primary transfer device 15Y, and a photoconductor cleaner 16Y are provided.

  The image forming mechanism 10 also includes an intermediate transfer belt 17 as an image carrier, a second transfer device 18, and a fixing device 19.

  The paper transport mechanism 20 is a mechanism that transports paper along a paper transport path r that passes through the second transfer device 18 and the fixing device 19 of the image forming mechanism 10, and a paper storage unit that stores paper on which an image is formed. Three paper trays 24a, 24b, and 24c, pick-up rolls 21a to 21c for picking up the papers stored in these paper trays 24a to 24c, the picked-up paper, the scooping rolls 22a to 22c, and the first one for transporting the paper 1 transport rolls 23a to 23e, a first sheet orientation correction mechanism 25 that corrects the orientation of the sheet, a transport belt 26 that transports the sheet from the second transfer unit 18 to the fixing unit 19, and a discharge roll that discharges the sheet to the outside. 26 and 27 are provided. The first paper attitude correction mechanism 25 is a second transport roll 255 that transports paper, and a registration roll that transports the paper transported from the second transport roll 255 to the second transfer unit 18 (hereinafter also simply referred to as a registration roll). ) 256, which is disposed between the second transport roll 255 and the registration roll 256, and includes guide members 251, 252, and 253 for guiding the paper along the curved paper transport path r. Of the guide members 251, 252, and 253, the guide member 251 disposed on the curved outer side of the sheet conveyance path r is rotatably disposed with one end fixed to the conveyance path. It is biased toward the inside. In the first paper attitude correction mechanism 25, a paper sensor 257 for detecting the presence or absence of paper is disposed upstream of the registration roll 256 in the paper transport direction c. The registration roll 256 corresponds to an example of the first roll referred to in the present invention.

  The re-feed conveyance mechanism 30 is a mechanism that inverts the paper on which the image is formed by the image forming mechanism 10 and conveys the paper to the paper conveyance mechanism 20 in order to form images on both sides of the paper. The reversing and conveying mechanism 32 and the sheet reversing unit 31 are provided with a duplex conveying roll 34 that conveys a sheet for forming a double-sided image. The sheet reversing unit 31 includes reversing rolls 311 and 312 that can be rotated forward and backward. When the reversing rolls 311 and 312 are rotated forward, the sheet discharged from the double-sided conveying roll 34 is sent to the reversing conveying path 313. Thereafter, the reversing rolls 311 and 312 are reversed to feed the sheet from the reverse conveying path 313 to the reverse conveying mechanism 32. This reverses the front and back of the paper. In the reverse conveyance path 313, the portion where the leading edge of the fed paper reaches is the reverse portion leading edge 31a, and the portion where the paper trailing edge at this time is located is the reverse portion trailing edge 31b. When the sheet fed to the reversing portion leading end 31 a is reversed and conveyed, the trailing end of the sheet located at the reversing portion rear end 31 b becomes the leading end and is sent out to the reversing conveyance mechanism 32.

  The reverse conveyance mechanism 32 includes re-feed rollers 321, 322, and 323 and a second paper attitude correction mechanism 33 that corrects the attitude of the paper, and conveys the paper in the re-feed conveyance direction e. The second paper attitude correction mechanism 33 includes a third transport roll 332 that transports the paper, a refeed standby roll 331 that sends the paper transported from the third transport roll 332 to the paper transport mechanism 20, and a third transport roll 332. And guide members 333 and 334 which are disposed between the paper re-feed standby roll 331 and guide the paper along the paper re-feed conveyance path s. The guide members 333 and 334 are made of a bent metal plate, and are disposed across a space in which the paper abutted against the refeed standby roll 331 is curved. A paper sensor 335 for detecting the presence / absence of paper is attached upstream of the refeed standby roll 331 in the refeed conveyance direction e, and a paper sensor 336 is installed downstream of the refeed standby roll 331. Is attached. The above-described paper sensors 257, 335, and 336 are all optical sensors, and detect the presence or absence of paper by detecting the brightness of incident light. The timing at which the paper is detected by the paper sensors 257, 335, and 336 is used for control of each mechanism by the control unit 40. Hereinafter, the paper sensors 335 and 336 are referred to as a first paper sensor 335 and a second paper sensor 336, and the paper sensor 257 is referred to as a third paper sensor 257. The first paper sensor 335 and the second paper sensor 336 correspond to an example of the first paper detection unit and the second paper detection unit according to the present invention, respectively. Further, the refeed standby roll 331 corresponds to an example of a second roll referred to in the present invention.

  The control unit 40 receives signals from various sensors installed in the image forming apparatus 1 and controls the operation of each mechanism of the image forming apparatus 1. Although not shown in the figure, the control unit 40 controls the overall operation of the image forming system based on a program, a ROM that stores programs and tables, and a temporary storage area in the CPU. It has a RAM to be provided and an interface circuit that relays signals between the outside of the control unit 40 and the CPU. Various functions provided by the control unit 40 are realized based on programs executed by the CPU. For example, the control unit 40 controls the operation of the rolls by controlling the driving of a motor (not shown) that rotationally drives the various rolls. Details of the function of the control unit 40 will be described later.

  The basic operation of the image forming apparatus 1 will be described. In the image forming unit 10Y, the photoconductor 11Y is rotationally driven in the direction of arrow a, and a charge is applied to the surface of the photoconductor 11Y by a charger. The exposure device 13Y forms an electrostatic latent image on the surface of the photoreceptor 11Y by irradiating the surface of the photoreceptor 11Y with exposure light based on image data corresponding to yellow of image data supplied from the outside. . The developing device 14Y forms a toner image by developing the electrostatic latent image with yellow toner. The yellow toner image is transferred to the intermediate transfer belt 17 by the primary transfer unit 15Y. After transfer, the toner remaining on the photoreceptor 11Y is removed by the photoreceptor cleaner 16Y. The intermediate transfer belt 17 is circularly moved in the direction of the arrow b by the intermediate transfer belt roll 17r, and the image forming units 10M, 10C, and 10K corresponding to colors other than yellow are respectively similar to the image forming unit 10Y. A toner image corresponding to the color is formed, and the toner image of each color is transferred onto the intermediate transfer belt 17 so as to overlap the toner image transferred by the image forming unit 10Y. In this way, the intermediate transfer belt 17 cyclically moves while carrying the toner image in response to the formation of the toner image.

  On the other hand, the paper is taken out from any selected one of the paper trays 24a to 24c by the pick-up rolls 21a to 21c, and the separating rolls 22a to 22c, the first transport rolls 23a to 23c, and the second transport roll 255. In addition, the sheet is transported in the direction of the arrow c by the registration roll 256. The registration roll 256 feeds the sheet toward the second transfer unit 18 at a timing synchronized with the formation of the toner image on the intermediate transfer belt 17. The second transfer unit 18 transfers the toner image from the intermediate transfer belt 17 to a sheet. The sheet is further conveyed to the fixing device 19 where the toner image is fixed. In this way, an image is formed on one side of the paper.

  When images are formed on both sides of a sheet, the sheet on which an image is formed on one side is conveyed to the sheet reversing unit 31 by a duplex conveying roll 34 and is rotated forward (rotation in the direction of arrow d) by the reversing rolls 311 and 312. It is sent to the reverse conveyance path 313. Thereafter, the sheet is conveyed in a state where the front and back sides are reversed by the reverse rotation of the reversing rolls 311 and 312, and is conveyed along the refeed conveyance path s. 1 paper attitude correction mechanism 25. Then, the second transfer device 18 and the fixing device 19 again transfer and fix the toner image on the back side surface, and an image is formed on both sides. Hereinafter, among the sheets on which images are formed on both sides, the surface on which an image is formed first is referred to as a first surface, and the surface on which an image is formed later is referred to as a second surface.

  When the image forming apparatus 1 forms an image on both sides of a plurality of sheets, the image forming apparatus 1 does not start the next sheet after completing the image formation on both sides of one sheet. After the image is formed on the first side of the sheet, the sheet is turned upside down by the refeed conveyance mechanism 30 and is conveyed again to the first sheet orientation correction mechanism 25 of the sheet conveyance mechanism 20 until the next time. One or a plurality of sheets are transported along a transport path r to form an image on the first surface. As for the first sheet that has been turned upside down and has reached the second sheet orientation correction mechanism 33 of the refeed conveyance mechanism 30, the next sheet is conveyed from the first sheet orientation correction mechanism 25. And is conveyed to the first paper attitude correction mechanism 25. Using this waiting time, the posture correction by the second paper posture correction mechanism 33 is performed.

  Next, the paper posture correction by the first paper posture correction mechanism 25 and the second paper posture correction mechanism 33 will be described.

  FIG. 2 is a diagram illustrating a state in which a sheet is conveyed by the first sheet attitude correction mechanism illustrated in FIG.

  As shown in part (a) of FIG. 2, the sheet P conveyed by the second conveying roll 255 is guided by the guide members 251 and 252 and proceeds in the direction of the registration roll 256 along the conveying path. At this time, the registration roll 256 is in a stopped state. As shown in part (b) of FIG. 2, after the sheet is abutted against the contact portions of the pair of registration rolls 256 that are in contact with each other, when the conveyance is continued by the conveyance roll 255, The degree of curvature of the portion between the two transport rolls 255 and the registration roll 256 is greater than the curvature of the original path shown in part (a) of FIG. 2, and pushes the guide member 251 outward. This increased paper curvature is called a loop. The paper is abutted against the registration roll 256 and a loop is formed, so that the edge of the front edge of the paper is aligned with the registration roll 256 and the skewed (skewed) paper posture is corrected. The extent to which the skew state is corrected by the first paper attitude correction mechanism 25 depends on the amount of loop formed. Further, the amount of the loop is controlled by the time during which the second transport roll 255 continues to transport the paper after the leading edge of the paper is abutted against the registration roll 256. More specifically, the loop amount is controlled by the time from when the third paper sensor 257 detects the paper until the second transport roll 255 stops the paper conveyance. For example, the amount of loop increases by increasing the time from when the third paper sensor 257 detects the paper until the second transport roll 255 stops transporting the paper.

  FIG. 3 is a diagram showing the movement of the paper conveyed through the first paper attitude correction unit.

  FIG. 3 shows the movement of the sheet with the passage of time t as a locus of the leading edge of the sheet. The sheet passes from the bottom of the diagram through the second transport roll 255, the third sheet sensor 257, the registration roll 256, and the transfer unit 18 shown in FIG. Here, the leading edge of the actual paper is abutted against the registration roll 256 and stops (time T1), but the second transport roll 255 continues to transport the paper during this time to form a paper loop. In the diagram, for convenience of understanding, the position of the registration roll 256 indicates that a loop is formed by continuing the conveyance of the sheet by the second conveyance roll 255 even after the leading edge of the sheet is abutted against the registration roll 256. It is shown as a horn-shaped part protruding more than. Therefore, the height of the square portion of the diagram represents the loop amount. Here, after the leading edge of the paper has passed through the third paper sensor 257, the time for the second transport roll 255 to continue transporting the paper to form a paper loop is defined as a loop formation time T1. The registration roll 256 resumes rotation in response to the reference signal TR, and sends the paper to the transfer unit 18. Here, the second transport roll 255 is set to be more than the timing of the reference signal TR for adjusting the phase of the motor. It must always stop for a certain time. This fixed time is referred to as setup time T2. In the first paper attitude correction mechanism 25, when forming a loop with the loop formation time T1, the leading edge of the paper needs to pass the third paper sensor 257 at a timing that is a time T1 + T2 ahead of the timing of the reference signal TR. is there. In other words, if the leading edge of the sheet cannot pass through the third sheet sensor 257 at a timing T1 + T2 before the timing of the reference signal TR, the sheet cannot be sent to the transfer unit 18 at the timing of the reference signal TR. Then, the toner image formed on the intermediate transfer belt 17 is not properly transferred, and paper jam occurs.

  FIG. 4 is a diagram for explaining how a loop is formed on a sheet by the second sheet attitude correction unit shown in FIG.

  Also in the second paper posture correction mechanism 33, the paper posture is corrected based on the same principle as the first paper posture correction mechanism 25 shown in FIG. In other words, after the sheet is abutted against the contact portion of the pair of refeed standby rolls 331 that are in contact with each other, and the conveyance by the third conveyance roll 332 is continued, the sheet conveyed on the plane is curved. Thus, a loop is formed. The loop amount is controlled by controlling the time during which the sheet is continuously conveyed by the third conveyance roll 332. In the second paper attitude correction mechanism 33, after the leading edge of the paper has passed through the first paper sensor 335, the time during which the third transport roller 332 continues to transport the paper and forms a paper loop is defined as a loop formation time.

  FIG. 5 is a functional block diagram of the image forming apparatus shown in FIG.

  The control unit 40 includes a mechanism control unit 41, a conveyance control unit 42, a refeed control unit 43, a timing generation unit 44, and a mode switching unit 45. A personal computer (PC) 60 is externally connected to the control unit 40.

  The mechanism control unit 41 controls the operation of each unit of the image forming mechanism 10 to form an image on a sheet. For example, according to the image signal transmitted from the personal computer 60, the operation of the image forming units 10Y, 10M, 10C, and 10K (see FIG. 1) is controlled to form a toner image corresponding to the image signal on the intermediate transfer belt 17. Let Further, the second transfer device 18 and the fixing device 19 are controlled to transfer and fix the toner image on the conveyed paper. When an image is formed on a plurality of sheets, toner images are formed in order based on the order in which the sheets are prepared by the sheet transport mechanism 20 and the refeed transport mechanism 30, and are transferred and fixed. The toner image is formed at predetermined intervals based on the image forming signal generated by the timing generation unit 44.

  The transport control unit 42 controls the operation of the paper transport mechanism 20 to transport the paper. For example, information on the timing at which the first paper sensor 335 or the second paper sensor 336 detects the paper is obtained, and the loop formation time T1 in the first paper attitude correction mechanism 25 is determined based on this information, and the loop formation is performed. An amount of loop according to time is formed on the paper. Further, the sheet is fed into the transfer unit 18 in accordance with the reference signal supplied from the timing generation unit 44.

  The re-feed control unit 43 controls the re-feed transport mechanism 30 so that the paper is reversed and transported. For example, the loop formation time in the second paper attitude correction mechanism 33 is determined, and a loop is formed on the paper.

  The timing generation unit 44 generates a reference signal that represents the timing at which the conveyance control unit 42 sends the paper to the paper conveyance mechanism 20 and an image formation signal that represents the timing at which the mechanism control unit 41 causes the image forming mechanism 10 to form a toner image. To do. The timing of the reference signal is synchronized with the timing of the image forming signal, and the interval changes depending on the operation mode. For example, in the normal mode, the timing generation unit 44 sets the timing of the reference signal at equal intervals. However, in the first high-speed mode described later, the timing corresponding to the second surface of the reference signal is higher than that in the normal mode. fast.

  The mode switching unit 45 obtains mode information representing a mode input by an operator's operation from the touch panel 50, and switches the operation mode based on the mode information. For example, the mode switching unit 45 switches the operation mode among a normal mode, a first high speed mode, and a second high speed mode. The second high-speed mode is a mode in which when the second paper posture correction mechanism 33 forms a loop, the first paper posture correction mechanism 25 omits the formation of the loop and passes the paper. The normal mode corresponds to an example of the first correction mode according to the present invention, and the second high speed mode corresponds to an example of the second correction mode according to the present invention.

  Next, a process in which the transport control unit 42 controls the first paper attitude correction mechanism 25 and a process in which the refeed control unit 43 controls the second paper attitude correction mechanism 33 will be described.

  FIG. 6 is a flowchart illustrating a first posture control process in which the conveyance control unit illustrated in FIG. 5 controls the first paper posture correction unit.

  In the first attitude control process, first, the conveyance control unit 42 determines whether or not the paper on which the first paper attitude correction mechanism 25 forms a loop is an image on the first surface, that is, the paper is a paper tray. It is determined whether the sheet has been conveyed from 24a to 24c or from the second sheet orientation correcting mechanism 33 (step S11). When the paper is a paper on which an image is formed on the first side that has been conveyed from the paper trays 24a to 24c (Yes), a predetermined loop formation time T1 that is predetermined for image formation on the first side of the paper. Is determined as the loop formation time (step S12), and the first paper orientation correction unit 25 is caused to form a loop with the determined loop formation time (step S16). On the other hand, when the sheet is a sheet on which an image is formed on the second side that has been conveyed from the second sheet attitude correction mechanism 33 (step S11: No), the operation mode is the second high-speed mode. Is determined (step S13). Here, when the operation mode is the second high-speed mode (Yes), and the paper posture is corrected by the second paper posture correction mechanism 33 (Step S14: Yes), the conveyance control unit. 42 omits the formation of a loop in the first paper attitude correction unit 25, passes the paper, and transports it to the transfer unit 18 (step S18). In other cases (step S13: No or step S14: No), the loop formation time T3 is determined according to the timing at which the second paper sensor detects the paper (step S15). Here, in the ROM (not shown) of the control unit 40, the transfer unit transfers the sheet at the timing of the reference signal according to the timing at which the second sheet sensor detects the sheet, which is obtained from the simulation or experiment in the design stage of the image forming apparatus. The value of the loop formation time that can be conveyed to 18 is stored in advance as a table, and the loop formation time T3 is determined by reading the value from this table. Here, a loop formation time shorter than the loop formation time T1 is stored in the table. Therefore, the loop formation time T3 determined in step S15 is predetermined for image formation on the first surface of the sheet. This is a time shorter than the loop formation time T1. Therefore, in the first paper attitude correction mechanism 25, the loop formation amount for the paper conveyed from the refeed conveyance mechanism 30 is smaller than the loop formation amount for the paper conveyed from the paper tray 24a. Further, the conveyance control unit 42 changes the loop formation time T3 according to the timing at which the paper P1R is detected by the second paper sensor 336. Thereby, the loop formation time is adjusted with respect to the delay in the conveyance of the sheet on which the image is formed on the second surface. Subsequently, the conveyance control unit 42 causes the first paper attitude correction mechanism 25 to form a loop at the determined loop formation time T3 (step S16), waits for the reception of the reference signal (step S17), and loads the paper. It is conveyed to the transfer unit 18. The combination of the first paper posture correction mechanism 25 and the conveyance control unit 42 that executes the first posture control process corresponds to an example of the first paper posture correction unit according to the present invention.

  FIG. 7 is a flowchart showing a second posture control process in which the refeed control unit shown in FIG. 5 controls the second paper posture correction mechanism.

  In the second attitude control process, the refeed control unit 43 first sets a limit timing that occurs every time a predetermined time elapses from the timing of the immediately preceding reference signal when the first sheet sensor 335 detects a sheet. Is determined (step S21). When the first sheet sensor 335 detects a sheet after a predetermined limit timing has elapsed (Yes), the refeed control unit 43 assumes that the sheet conveyance is particularly delayed, and the second sheet attitude correction mechanism 33. The loop formation is omitted, and the second paper attitude correction mechanism 33 is passed. On the other hand, when the sheet detection timing by the first sheet sensor 335 is before the limit timing elapses (Yes), the refeed control unit 43 forms a loop according to the timing at which the first sheet sensor 335 detects the sheet. The time is determined (step S22), and the loop is formed in the second paper attitude correction mechanism 33 with the determined loop formation time (step S23). In the ROM (not shown) of the control unit 40, a loop formation time value corresponding to the timing at which the first paper sensor 335 detects the paper obtained in the design stage of the image forming apparatus is also stored in advance as a table. The formation time is determined by reading a value from this table. In the table, the larger the timing value at which the first paper sensor 335 detects the paper, the smaller the loop formation time value is stored. The refeed control unit 43 uses the first paper sensor 335 to store the paper. The later the timing at which is detected, the shorter the loop formation time. Next, the refeed control unit 43 causes the first sheet orientation correction mechanism 25 to convey the sheet (step S24). The combination of the second paper posture correction mechanism 33 and the refeed control unit 43 that executes the second posture control processing corresponds to an example of the second paper posture correction unit according to the present invention.

  Next, an operation of forming an image on both surfaces of a plurality of sheets by the image forming apparatus 1 having the above-described configuration will be described with reference to FIGS. 1 and 8.

  FIG. 8 is a diagram showing the movement of a plurality of sheets conveyed through the image forming apparatus shown in FIG.

  FIG. 8 shows the movement of the three sheets P1, P2, and P3 with the passage of time t as the locus of the leading edge of each sheet. A symbol of “F” is attached to the code of the sheet conveyed to form an image on the first surface, and is indicated by a solid line. The symbol of the sheet conveyed to form an image on the second surface is indicated by a broken line with the symbol “R”. First, paying attention to the first sheet P1, the sheet P1F taken out from the sheet tray 24a by the pickup roll 21a is conveyed by the separation roll 21a, the first conveyance roll 23a, and the second conveyance roll 255, and is registered. It is abutted against 256 and a loop is formed. Thereafter, the sheet P1F is sent to the transfer device 18 at the timing of the reference signal TR1, and the toner image is transferred and fixed, further conveyed by the double-sided conveyance roll 34 and the reverse roll 312, and reaches the reverse portion tip 31a. Thereafter, when the reversing rolls 311 and 312 are reversed, the paper P1F becomes the paper P1R, and the paper is fed in reverse with the rear end of the paper positioned at the rear end 31b (lower end in the diagram) being the front end. Then, it reaches the refeed standby position where the refeed standby roll 331 is located. The sheet P1R is abutted against the refeed standby roll 331, and a loop having a loop amount corresponding to the loop formation time is formed, and the posture is corrected. Thereafter, the sheet P1R is abutted against the registration roll 256 via the second transport roll 255, and the posture is corrected by forming a loop. Thereafter, the sheet P1R is sent to the transfer unit 18 at the timing of the reference signal TR4, and the toner image is transferred, fixed, and discharged.

  Next, paying attention to the second sheet P2F, the second sheet P2F is transported to the first sheet orientation correction mechanism 25 again after an image is formed on the first surface of the first sheet P1. An image is formed using the time until the image is received. In this way, the image formation of the next sheet P2 is performed in the time between the formation of the image on the first side of the sheet P1 and the formation of the image on the second side.

  After the first sheet P1F with the front and back reversed is conveyed again to the first sheet attitude correction mechanism 25, the first and second surfaces of the sheet are processed alternately. In response to this, the image forming units 10Y, 10M, 10C, and 10K form toner images on the intermediate transfer belt 17.

  In the diagram of FIG. 8, the locus of the paper P1F from the first conveyance roll to the vicinity of the registration roll is sandwiched between two broken lines. The two broken lines are the first conveyance roll 23a and the second conveyance roll. The range in which the sheet P1F can be fed into the transfer unit 18 at an appropriate timing while the predetermined loop formation time T1 is secured by adjusting the conveyance speed by 255 is shown. This range is set not only for the paper P1F but also for the other papers P2F, P3F, etc., and the paper P1R, P2R for the second surface, but is not shown for ease of viewing the diagram.

  Here, in the diagram of FIG. 8, the first sheet P1R on which the image is formed on the second surface is delayed from the normal conveyance in the refeed conveyance path s and can be adjusted to be set to P2R. The registration roll 256 is reached later than this range.

  FIG. 9 is an enlarged view of the diagram of FIG. 8, showing the movement of the paper P1R near the registration roll.

  As shown in FIG. 9, the sheet P1R exceeds the range in which the sheet P1R can be fed into the transfer device 18 at an appropriate timing while ensuring a predetermined loop formation time T1 (see FIG. 3), and the registration roll 256 is delayed. Has reached. The delay of the sheet P1R is detected as the timing at which the second sheet sensor 336 detects the sheet. Specifically, the transport control unit 42 (see FIG. 5) measures the detection time T4 from the timing of the reference signal TR3 to the timing at which the paper P1R is detected by the second paper sensor 336. The conveyance control unit 42 determines a shortened loop formation time T3 corresponding to the detection timing (see step S15 in FIG. 6). As a result, the conveyance control unit 42 forms a loop with a small loop amount corresponding to the loop formation time T3 shorter than the predetermined loop formation time T1 (see step S16 in FIG. 6).

  Here, if the transfer control unit 42 forms a loop at the loop formation time T1 shown in FIG. 3 without changing the loop formation time, at the timing of the reference signal TR4 as shown by a locus indicated by NG in FIG. The sheet cannot be fed into the transfer unit 18. However, when the paper is transported from the re-feed transport mechanism 30, the loop formation amount in the first paper attitude correction mechanism 25 is changed to be small according to the timing at which the second paper sensor 336 detects the paper P1R. Therefore, even if the conveyance of the sheet is delayed, the sheet can be sent to the transfer unit 18 at the timing of the reference signal TR4 as shown by the solid line in FIG.

  Next, returning to FIG. 8, the description will be continued. The second sheet P2R on which the image is formed on the second surface is set in advance, which is later than the normal conveyance in the refeed conveyance path s. The paper re-feed standby roll 331 is reached later than the adjustable range.

  FIG. 10 is an enlarged diagram of the diagram of FIG. 8 and shows the movement of the paper P2R near the refeed standby roll.

  As shown in FIG. 10, the sheet P2R exceeds the range (P2Ra) that can be conveyed to the first sheet attitude correction mechanism 25 at an appropriate timing while ensuring a predetermined loop formation time T15, and is delayed. Re-feed standby roll 331 has been reached. Here, the appropriate timing is a timing at which the first paper attitude correction mechanism 25 can send the paper to the transfer device 18 in accordance with the timing of the reference signal. In this case, the timing at which the first paper sensor 335 detects the paper P2R is delayed. The paper refeed control unit 43 (see FIG. 5) counts the detection time T12 from the timing of the immediately preceding reference signal TR5 to the timing at which the paper P2R is detected by the first paper sensor 335, and according to this detection timing. The shortened loop formation time T14 is determined (see step S21 in FIG. 7). Then, the refeed control unit 43 forms a loop with a small and changed loop amount corresponding to the determined loop formation time T14 (see step S23 in FIG. 7).

  Here, if the paper refeed control unit 43 does not change the loop formation time and forms a loop at the loop formation time T15 shown in FIG. 10, the first paper posture correction mechanism 25 causes the paper to be fed at an appropriate timing. Can not be transported to. However, since the loop formation amount in the second paper attitude correction mechanism 33 is changed to be small according to the timing at which the first paper sensor 335 detects the paper P2R, the paper is fed to the first paper attitude correction mechanism at an appropriate timing. It is conveyed to 25.

  Here, FIG. 10 also shows a locus P2Rb when the conveyance of the paper P2 is further delayed. In this case, the paper refeed control unit 43 (see FIG. 5) omits the loop formation in the second paper attitude correction mechanism 33 according to the time T13 until the paper is detected, and removes the paper P2Rb. Pass (see Step S21: Yes in FIG. 7) and transport to the first paper attitude correction mechanism 25.

  In this way, by adjusting the loop formation time in the first paper attitude correction mechanism 25 and the second paper attitude correction mechanism 33, the paper is conveyed at an appropriate timing as shown in FIG.

  If the loop formation time is not adjusted, a paper jam occurs. Further, in order to avoid paper jamming, the order of forming toner images is delayed in the image forming units 10Y, 10M, 10C, and 10K. Since the first surface and the second surface are processed alternately, the rhythm of processing is disturbed.

  FIG. 11 is a diagram showing the movement of the paper when the order in which the toner images are formed is delayed as a comparative example. FIG. 12 is a diagram illustrating the order in which images are formed on paper.

  As shown in FIG. 11, since the image formation on the second surface of the paper needs to be performed during the formation of the image on the first surface of the other paper, the paper is kept waiting for a long time at the paper standby position. It will be.

  The row (a) in FIG. 12 shows the order in which images are formed on the paper when the images are formed on the paper at the timing shown in FIG. 8, and the three papers P1, P2, and P3 are shown. On the other hand, an image is formed in a small free time in the order of P1 table (F), P2F, P1 back (R), P3F, P2R, and P3R. However, when an image is formed on the sheet at the timing shown in FIG. 11, the timing at which the image is formed on the back (R) of the first sheet P1 is delayed as shown in the row (b) of FIG. End up.

  Next, the second high speed mode will be described.

  13 and 14 are diagrams for explaining the second high-speed mode of the image forming apparatus 1 shown in FIG.

  In the image forming apparatus 1, in the first paper attitude correction mechanism 25, the loop formation amount for the paper conveyed from the refeed conveyance mechanism 30 is smaller than the loop formation amount for the paper conveyed from the paper tray 24a. (See step S15 in FIG. 6). For example, in the second high speed mode, as shown in FIG. 13, the first paper attitude correction mechanism 25 sets the loop formation time for the paper conveyed from the paper tray 24a to T1 as shown in FIG. The loop formation time for the paper transported from the re-feed transport mechanism 30 is set as a time within T4. Further, in the second high-speed mode, the timing generation unit 44 sets the output timing of the reference signal for sending the paper transported from the refeed transport mechanism 30 to the transfer unit 18 from the output timing of the paper reference signal. Also speed up. For example, as shown in FIG. 13, a reference signal TR4A with an earlier output timing is output. For this reason, in the second high-speed mode, as shown in FIG. 14, the time TA for forming an image on the second surface of the paper is shortened than the time TP for forming an image on the first surface.

  Subsequently, a second embodiment and a third embodiment of the present invention will be described.

  The image forming apparatuses according to the second embodiment and the third embodiment of the present invention differ from the image forming apparatus 1 according to the first embodiment described above only in the configuration of the second paper attitude correction mechanism, and the other configurations are the same. Therefore, only the paper attitude correction mechanism will be described.

  FIG. 15 is a schematic configuration diagram illustrating a second paper attitude correction mechanism according to the second embodiment.

  The second paper attitude correction mechanism shown in FIG. 15 includes guide members 1333, 1334, and 1335 between the third transport roll 1332 that transports the paper and the refeed standby roll 1331. The guide member 1335 is made of an elastic member, and is a cantilever spring whose edge far from the guide member 1334 arranged side by side along the path along which the sheet is conveyed is fixed to the path. In the second paper attitude correction mechanism shown in FIG. 15, the paper on which the loop is formed pushes the guide member 1335 outward. The guide member 1335 is pushed out and elastically deformed, and a loop formed on the paper is suppressed by this elastic force. The leading edge of the sheet is strongly pressed by the refeed standby roll 1331 as compared with the case where the sheet is not provided, due to the force received from the guide member 1335. Therefore, the leading end is aligned with the refeed standby roll 1331 with a strong force.

  FIG. 16 is a schematic configuration diagram illustrating a second paper attitude correction mechanism according to the third embodiment.

  The second paper posture correction mechanism shown in FIG. 16 includes guide members 2333, 1334, and 2335 between the third transport roll 2332 that transports the paper and the refeed standby roll 2331. The guide members 2333, 1334, and 2335 are baffle chutes arranged so as to form a curved path, and the guide member 2335 arranged outside the curve is urged by the elastic member 2336 toward the inside of the curve. ing. In the second paper attitude correction mechanism shown in FIG. 16, the paper on which the loop is formed pushes the guide member 2335 outward. When the guide member 2335 is pushed outward, the elastic member 2336 is elastically deformed, and the guide member 2335 is pulled back by this elastic force. The leading edge of the sheet is strongly pressed by the refeed standby roll 1331 by the reaction force received from the elastic member 2336 through the guide member 2335. Accordingly, the leading end is aligned with the refeed standby roll 2331 with a strong force.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. FIG. 3 is a diagram illustrating a state in which a sheet is conveyed by a first sheet attitude correction mechanism illustrated in FIG. 1. 6 is a diagram illustrating movement of a sheet conveyed through a first sheet attitude correction mechanism. FIG. 6 is a diagram illustrating a state in which a loop is formed on a sheet by the second sheet attitude correction mechanism illustrated in FIG. 1. FIG. 2 is a functional block diagram of the image forming apparatus illustrated in FIG. 1. 6 is a flowchart showing a first attitude control process in which the conveyance control unit shown in FIG. 5 controls a first paper attitude correction mechanism. 6 is a flowchart illustrating a second attitude control process in which a refeed control unit shown in FIG. 5 controls a second sheet attitude correction mechanism. 2 is a diagram illustrating movement of a plurality of sheets conveyed through the image forming apparatus illustrated in FIG. 1. FIG. 9 is an enlarged diagram of the diagram of FIG. 8 showing the movement of the paper P1R near the registration roll. FIG. 9 is an enlarged diagram of the diagram of FIG. 8 showing the movement of the paper P2R in the vicinity of the refeed standby roll. As an example of comparison, a diagram illustrating the movement of a sheet when the order in which toner images are formed is delayed. FIG. 4 is a diagram illustrating the order in which images are formed on paper in the image forming apparatus. 3 is a diagram for explaining a second high-speed mode of the image forming apparatus 1 shown in FIG. 1. 3 is a diagram for explaining a second high-speed mode of the image forming apparatus 1 shown in FIG. 1. It is a schematic block diagram which shows the 2nd paper attitude | position correction mechanism which concerns on 2nd Embodiment. It is a schematic block diagram which shows the 2nd paper attitude | position correction mechanism which concerns on 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Image forming mechanism 20 Paper conveyance mechanism 24a, 24b, 24c Paper tray 25 First paper attitude correction mechanism 256 Registration roll (first roll)
30 Re-feed transport mechanism 33 Second paper attitude correction mechanism 331 Re-feed standby roll (second roll)
40 Control Unit 335 First Paper Sensor 336 Second Paper Sensor

Claims (8)

An image forming unit that forms an image on the conveyed paper;
A paper storage unit that stores a paper on which an image is formed in the image forming unit, and a paper transport unit that transports the paper on a paper transport path passing through the image forming unit;
In order to form the image on both sides of the paper by transporting the paper on which the image is formed in the image forming unit to the paper transport unit again, the paper is transported upside down and transported to the paper transport unit. With
The paper transport unit has a pair of first rolls that come into contact with each other, and a paper is abutted against the first roll to form a loop, thereby correcting the posture of the paper. Part
The re-feed conveyance unit has a pair of second rolls that come into contact with each other, and a second paper that corrects the posture of the paper by the paper being abutted against the second roll to form a loop. Equipped with a posture correction unit,
The first paper attitude correction unit changes an amount of forming a loop on the paper depending on whether the paper is conveyed from the paper storage unit or from the refeed conveyance unit. An image forming apparatus. The re-feed conveyance unit includes a first paper detection unit that detects the presence or absence of a sheet on the upstream side of the second roll in the re-feed conveyance direction in which the sheet is conveyed toward the sheet conveyance unit. Prepared,
2. The image according to claim 1, wherein the second paper attitude correction unit changes an amount of forming a loop on the paper according to a timing at which the first paper detection unit detects the paper. Forming equipment. The re-feed conveyance unit includes a first paper detection unit that detects the presence or absence of a sheet on the upstream side of the second roll in the re-feed conveyance direction in which the sheet is conveyed toward the sheet conveyance unit. Prepared,
The second paper attitude correction unit is configured to pass the paper without forming a loop when the first paper detection unit detects the paper after a predetermined timing has elapsed. The image forming apparatus according to claim 1, wherein: The re-feed conveyance unit includes a second paper detection unit that detects the presence or absence of a sheet on the downstream side of the second roll in the re-feed conveyance direction in which the sheet is conveyed toward the sheet conveyance unit. Prepared,
2. The image according to claim 1, wherein the first paper attitude correction unit changes an amount of forming a loop on the paper according to a timing at which the second paper detection unit detects the paper. Forming equipment.   The first paper attitude correction unit is configured to make an amount of forming a loop on the paper conveyed from the refeed conveyance unit smaller than an amount of forming a loop on the paper conveyed from the paper storage unit. The image forming apparatus according to claim 1, wherein:   A first correction mode in which the image forming apparatus causes the first paper posture correction unit to form a paper loop even when the second paper posture correction unit forms a paper loop; and A second correction mode in which when the second paper attitude correction unit forms a loop on the paper, the paper loop is not formed by the first paper attitude correction unit and the paper is allowed to pass; The image forming apparatus according to claim 1, further comprising a correction mode switching unit that switches between the two.   2. The second sheet attitude correction unit includes a guide member made of an elastic member that suppresses a loop formed on a sheet abutted against the second roll. Image forming apparatus.   2. The second sheet posture correcting unit includes a baffle chute urged by an elastic member that guides the second curved sheet to the second roll. Image forming apparatus.

Images