JP2007298874A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus carrying out early detection of paper jamming while suppressing deterioration in productivity. <P>SOLUTION: The image forming apparatus 1 includes an image forming part 10 forming an image on transported paper and a paper transporting part 20 sequentially transporting a plurality of pieces of paper on a paper transporting path R passing the image forming part 10. The paper transporting part 20 includes; a paper reversing transporting path 291 installed downstream in the image forming part 10 in the paper transporting path R and on which the paper with an image formed on it at the image forming part 10 is transported, a paper sensor 297 installed on the paper reversing transporting path 291 detecting existence of the paper and a reversing transporting part 296 transporting the paper transported on the paper reversing transporting path 291 in an opposite direction to the direction the paper was transported on the paper reversing transporting path 291 while evading detection of existence of paper by the paper sensor 297. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

Some image forming apparatuses represented by copiers and printers have a paper reversing function for reversing the front and back of a sheet on which an image has been formed. An image forming apparatus having a sheet reversing function forms an image on both sides of a sheet by, for example, reversing the front and back of a sheet on which an image is formed on one side and forming an image again. The paper reversing function is also used when reversing the page order when a plurality of pages of paper are discharged. Here, in Patent Document 1, a path for discharging the sheet to the discharge tray and a return path having a roll that can be rotated forward and backward are provided downstream of the fixing device that fixes the toner on the sheet in the sheet conveyance direction. An image forming apparatus that realizes a sheet reversing function is disclosed. The roll arranged in the return path forwards and conveys the sheet conveyed from the fixing device, and when most of the sheet is sent out, it reverses and starts reversing and discharging the sheet. The image forming apparatus allows the preceding sheet to overlap the succeeding sheet when the succeeding sheet enters the returning path when the preceding sheet is reversed and discharged by the roll. The conveyance interval of subsequent sheets is shortened.
JP-A-8-59046

  In the image forming apparatus of Patent Document 1, in order to reverse the roll by detecting the conveyance state of the paper, sensors are provided on both the front side and the back side of the roll as viewed from the fixing device. However, among these sensors, the paper passage timing detected by the back sensor and the timing at which the paper trailing edge approaches the roll differ depending on the paper size and the conveyance speed, and the paper trailing edge has approached the roll. In order to detect accurately, it is necessary to arrange a sensor on the near side of the roll in the vicinity of the roll and detect the passage of the rear end of the sheet by this sensor.

  However, in the image forming apparatus of Patent Document 1 in which the sheet conveyed from the fixing device overlaps the preceding sheet that has been reversed and discharged, if the sensor on the near side of the roll is arranged near the roll, the rear end of the sheet is passed. Although it is possible to accurately detect, it is not possible to detect the passage of the leading edge of the succeeding sheet that overlaps the preceding sheet. The detection result from the sensor is also used for determining a paper jam. If the passage of the front end of the paper cannot be detected, the detection of the paper jam is delayed. In particular, the fixing device that feeds the paper to the return path strongly conveys the paper with a pair of rolls, so if the paper is jammed on the downstream side, if the conveyance operation is not stopped quickly, There is a risk of damage.

  SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an image forming apparatus capable of early detection of a paper jam while suppressing a decrease in productivity.

An image forming apparatus of the present invention that achieves the above object includes an image forming unit that forms an image on a conveyed sheet;
A sheet conveying unit that sequentially conveys a plurality of sheets on a sheet conveying path passing through the image forming unit,
The paper transport unit is
A paper reversing conveyance path on which the paper on which an image is formed in the image forming unit is conveyed downstream of the image forming unit in the paper conveyance path;
A paper sensor disposed on the paper reversing conveyance path for detecting the presence or absence of paper;
A reversing conveyance unit configured to convey the sheet conveyed to the sheet reversing conveyance path in a direction opposite to the direction in which the sheet has been conveyed to the sheet reversing conveyance path while avoiding detection of the presence of the sheet by the sheet sensor; It is provided with.

  In the image forming apparatus of the present invention, the preceding sheet on which an image is formed in the image forming unit and conveyed to the sheet reversing conveyance path is detected by the sheet sensor, and then the direction conveyed to the sheet reversing conveyance path is When the paper is conveyed in the opposite direction, the paper is reversed. Next, when the succeeding sheet of this sheet is conveyed to the sheet reversal conveyance path and is detected by the sheet sensor, the reversal conveyance unit conveys the preceding sheet in the opposite direction while avoiding detection of the presence of the sheet by the detection sensor. Therefore, it is possible to detect the subsequent sheet unloaded from the image forming unit at an early stage without being obstructed by the preceding sheet. Therefore, according to the image forming apparatus of the present invention, paper jam can be detected at an early stage without reducing productivity.

  Further, in the image forming apparatus of the present invention, the reversing conveyance unit includes a pair of reversing rolls that are freely reversible and that feeds a sheet to the sheet conveying path and sends the sheet from the sheet reversing conveying path. The reversing roll is further movable in the direction of the rotation axis and moves in the direction of the rotation axis, thereby moving the sheet in the width direction perpendicular to the sheet conveyance direction to a position where detection of the presence of the sheet by the sheet sensor is avoided. Preferably there is.

  The reversing conveyance unit includes a reversing roll that can be rotated in the forward and reverse directions and movable in the direction of the rotation axis, and the paper is moved in the width direction by the movement of the reversing roll. Is achieved with a simple configuration.

  Here, the image forming apparatus of the present invention includes a sensor position adjustment unit that obtains paper size information representing the size of the paper and moves the paper sensor in the width direction based on the paper size information. preferable.

  In an image forming apparatus that employs a so-called center registration method in which papers having various sizes are handled with the center position in the width direction aligned, the position of the side edge with respect to the paper conveyance direction depends on the paper size. Change. As the paper sensor moves in the width direction based on the paper size information, the paper jam is appropriately detected even in the center registration method.

  In the image forming apparatus of the present invention, the pair of reversing rolls move in the direction of the rotation axis while avoiding the time when the paper sandwiched between the reversing rolls is sandwiched between rolls other than the reversing roll. Preferably there is.

  When a plurality of pairs of rolls are arranged on the sheet conveyance path and one sheet is sandwiched between a plurality of pairs of rolls including a reversing roll, if the reversing roll moves in the rotation axis direction, the sheet is twisted or skewed. There is a risk. The reversing roll moves while avoiding the time when the paper is pinched by a roll other than the reversing roll, thereby suppressing the occurrence of twisting and skewing of the paper.

  As described above, according to the present invention, an image forming apparatus capable of early detection of a paper jam while suppressing a decrease in productivity is realized.

  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 an embodiment of the present invention.

  The image forming apparatus 1 shown in FIG. 1 includes an image forming mechanism 10, a paper transport mechanism 20, a control unit 50 that controls the operation of the entire image forming apparatus 1, and a paper tray 40 (40a, 40b, 40) that stores paper. 40c, 40d) and a touch panel 60 for inputting various information by the operation of the operator.

  The image forming mechanism 10 forms an image on conveyed paper, and includes a scanner 11, a photosensitive drum 12 as an image carrier, a charger 13 for uniformly charging the photosensitive drum 12, and an electrostatic charge. A developing unit 14 that develops the latent image into a toner image, a transfer unit 15 that transfers the toner image onto the paper, a fixing unit 16 that fixes the toner on the paper, and a cleaner 17 that collects the residual toner that has not been transferred. An image is formed on a sheet by an electrophotographic method. An image signal transmitted from the outside is converted into a signal by exposure light in the scanner 11, and an electrostatic latent image based on the image signal is formed on a rotating cylindrical photosensitive drum 12. The electrostatic latent image is formed by the scanner 11 scanning the surface of the photosensitive drum 12 with exposure light in the direction of the rotation axis of the photosensitive drum 12. The electrostatic latent image is developed by the developing unit 14 to obtain a toner image. The toner is transferred by the transfer unit 15 to the sheet conveyed through the sheet conveyance path R. Thereafter, the residual toner is removed from the photosensitive drum 12 by the cleaner 17, and the photosensitive drum 12 is charged by the charger 13. On the other hand, the sheet onto which the toner has been transferred by the transfer unit 15 is pressed and heated by a pair of fixing rolls 16a included in the fixing unit 16, and the toner image is fixed on the sheet. The fixing roll 16a conveys the paper with strong clamping.

  The paper transport mechanism 20 sequentially transports the paper on the paper transport path R passing through the image forming mechanism 10, and picks up rolls 21a to 21d that take out the paper stored in the paper trays 40a to 40d. Scrape paper, roll 22a to 22d, transport paper to transfer unit 15, transport rolls 23a to 23e and registration roll 24, transport belt 25 to transport paper from transfer unit 15 to fixing unit 16, and paper Discharging rolls 26 and 27 for discharging are provided. The paper transport mechanism 20 is disposed downstream of the fixing unit 16 of the image forming mechanism 10 on the paper transport path R, and reverses and transports a reverse transport unit 29 that reverses and transports the paper on which the image is formed. A refeed unit 31 that transports the reversed paper to the image forming mechanism 10 again is also provided. The refeed unit 31 includes a plurality of refeed conveyance rolls 31a.

  The control unit 50 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, the control unit 50 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. The RAM includes an interface circuit that relays signals between the CPU and the outside of the control unit 50 and the CPU. Various functions provided by the control unit 50 are realized based on programs executed by the CPU. The function of the control unit 50 will be described later.

  FIG. 2 is a schematic configuration diagram showing the reverse conveyance unit shown in FIG. 1 and its peripheral portion.

  In FIG. 2, the reverse conveyance unit 29 is shown together with two sheets being conveyed.

  The reverse conveyance unit 29 includes a paper reverse conveyance path 291 through which the paper on which an image is formed by the image forming mechanism 10 (see FIG. 1) is conveyed, an introduction path 292 that guides the paper to the paper reverse conveyance path 291, and a paper A reverse discharge path 293 branched from the reverse conveyance path 291 and a double-sided branch path 294 are provided. An introduction roll 295 for conveying paper is disposed in the introduction path 292, and a reverse conveyance direction opposite to the direction A in which the paper conveyed from the introduction path 292 is conveyed in the paper reverse conveyance path 291. A pair of reversing rolls 296 transported to B and a paper sensor 297 for detecting the presence or absence of paper are arranged. The reversing roll 296 can be rotated forward and backward. When the reversing roll 296 is rotated forward, the sheet is fed from the introduction path 292 to the sheet reversing conveyance path 291 and is reversed to send the sheet from the sheet reversing conveyance path 291 to the reversing discharge path 293. In the paper reversal conveyance path 291, there are two directions: the direction in which the paper fed from the introduction path 292 goes to the back of the paper reverse conveyance path 291 and the direction from the back of the paper reverse conveyance path 291 to the reverse discharge path 293. The paper moves. The reversing roll 296 is configured to be movable in the rotation axis direction. The paper sensor 297 is an optical sensor disposed on the front side of the reversing roll 296 when viewed from the image forming mechanism 10 (see FIG. 1), and detects the presence or absence of paper by detecting the brightness of incident light. Detect. The paper that has been toner-fixed by the fixing unit 16 of the image forming mechanism 10 and carried out from the discharge roll 26 is normally discharged from the discharge roll 27 via the discharge path 271, but is output with the front and back reversed. In this case, it is guided to the introduction path 292 by switching a gate (not shown), and further conveyed to the paper reversal conveyance path 291 by the introduction roll 295. When the leading edge of the conveyed paper passes the position of the paper sensor 297, the paper sensor 297 detects the presence of paper. By detecting the presence of paper by the paper sensor 297, it is detected that the paper has been normally conveyed from the fixing unit 16 to the paper sensor 297 without being jammed. The sheet is further conveyed to the back of the sheet reversal conveyance path 291 by a reversing roll 296 that rotates forward (rotates in the direction opposite to the arrow in the drawing). Eventually, when the trailing edge of the paper passes the position of the paper sensor 297, the paper sensor 297 detects the absence of paper. By detecting the absence of paper, it is detected that the trailing edge of the paper has approached the reverse roll 296. At this time, the reverse roll 296 transports the paper in the reverse transport direction B opposite to the transported direction by reversing in the direction of the arrow in the figure. That is, the paper sensor 297 disposed on the front side of the reversing roll 296 includes a sensor for detecting a paper jam of the paper carried out from the fixing unit 16 and a sensor for detecting a timing at which the reversing roll 296 is reversed. I also use it. Hereinafter, conveying the paper in the reverse conveyance direction B is referred to as reverse conveyance. The reversely conveyed sheet passes through the reverse discharge path 293 and is discharged to the outside by the discharge roll 27. As a result, the sheet transported from the fixing unit 16 (see FIG. 1) is transported out of the image forming apparatus 1 with the reverse side reversed by the reverse transport unit 29.

  When a plurality of sheets are sequentially carried out from the fixing unit 16, even when the preceding sheet is reversed and carried out through the reverse discharge path 293 by the reverse roll 296, the subsequent sheet is carried out to the reverse conveyance unit 29 and is reversed. It is conveyed to the discharge path 293. In FIG. 2, when the preceding sheet P1 of the two sheets P1 and P2 is reversed and carried out on the sheet reversal conveyance path 291 by the reversing roll 296, the succeeding sheet P2 is discharged to the discharge roll 26 and the introduction roll 295. The state of being conveyed to the sheet reversal conveyance path 291 via the introduction path 292 is shown. At this time, the two sheets P1 and P2 in the sheet reversal conveyance path 291 have overlapping portions. However, in the image forming apparatus 1 according to the present embodiment, the reversing roll 296 detects the preceding sheet P1 to be reversed and conveys the sheet sensor 297. Is moved in the width direction perpendicular to the paper transport direction A to a position where detection of the presence of the paper is avoided. Thereby, the paper sensor 297 detects the passage of the succeeding paper P2 at the leading end of the succeeding paper P2.

  When an image is also formed on the back side of a sheet on which an image is formed on one side, the sheet in the sheet reversal conveyance path 291 is conveyed to the duplex branch path 294 by switching a gate (not shown) and passes through the refeed unit 31. Then, it is conveyed again to the image forming mechanism 10.

  FIG. 3 is a schematic configuration diagram illustrating the paper sensor, the reversing roll, and the peripheral portion thereof illustrated in FIG.

  FIG. 3 shows an arrangement of the reversing roll 296 and the paper sensor 297 as viewed from the side on which the discharge roll 27 is disposed in the image forming apparatus 1 (see FIG. 1). The motors 296R and 296S are also shown. The image forming apparatus 1 according to the present embodiment employs a so-called side registration method, and conveys all the sheets having various sizes with one side edge aligned with a reference position. For example, the paper P conveyed from the fixing unit 16 (see FIG. 1) via the introduction path 292 (see FIG. 2) has the side edge Ps aligned with the reference position S. The paper sensor 297 is fixed at a predetermined distance x1 from the reference position S in the width direction. The reverse roll 296 is driven by a rotational drive motor 296R and a shift motor 296S. The rotational drive motor 296R conveys and reversely conveys the paper by rotating the reverse roll 296 forward and backward. The shift motor 296S moves the sheet sandwiched between the reversing rolls 296 in the width direction by moving the reversing rolls 296 in the direction of the rotation axis. The combination of the reversing roll 296 of the present embodiment, the rotation drive motor 296R, and the shift motor 296S corresponds to an example of a reversing conveyance unit according to the present invention. When the reverse roll 296 rotates forward, the paper P is fed downward, that is, toward the back of the paper reverse conveyance path 291 (see FIG. 2), and when the rear end Pe of the paper passes the paper sensor 297, the reverse roll 296 is transferred. Stops and moves in the direction of the arrow by a predetermined distance longer than the distance x1 with the paper P sandwiched therebetween. Then, the reverse roll 296 starts reverse rotation, and the paper P is reversely conveyed upward. At this time, since the paper P has been moved in the width direction to a position where the paper sensor 297 avoids detecting the presence of the paper, the paper sensor 297 does not detect the presence of the paper P. In this way, the function of reversing and conveying the sheet P conveyed to the sheet reversing conveyance path 291 while avoiding detection of the presence of the sheet by the sheet sensor 297 is realized with a simple configuration.

  FIG. 4 is a functional block diagram of the image forming apparatus shown in FIG.

  The control unit 50 includes a mechanism control unit 51, a conveyance control unit 52, and a reverse conveyance control unit 53. A personal computer (PC) 70 is externally connected to the control unit 50.

  The mechanism control unit 51 controls the operations of the units 11 to 17 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 70, the operation of the scanner 11 (see FIG. 1) is controlled.

  The transport control unit 52 controls the operation of the paper transport mechanism 20 other than the reverse transport unit 29 to transport the paper. For example, the transport control unit 52 selects a paper tray of paper to be transported by the paper transport mechanism 20 based on paper size information input from the touch panel 60 by an operator's operation. Further, the operation of the fixing unit 16 (see FIG. 1) is controlled to fix the toner on the paper. Furthermore, the conveyance control unit 52 receives a signal from the paper sensor 297 when the reverse conveyance unit 29 is used to reverse the front and back of the paper. Specifically, if a paper presence signal is not received from the paper sensor 297 even after a predetermined time has elapsed since the fixing of the toner on the paper by the fixing unit 16, it is determined that a paper jam has occurred, The operation of the paper transport mechanism 20 is stopped, and the mechanism control unit 51 is made to stop the operation of the image forming mechanism 10.

  The reverse conveyance control unit 53 receives a signal from the paper sensor 297 and controls the operation of the reverse conveyance unit 29. Specifically, the rotation driving motor 296R and the shift motor 296S of the reversing and conveying unit 29 are controlled, and the reversing roll 296 is moved in the forward and reverse directions and the rotation axis direction to control the sheet reversing and conveying operation.

  The combination of the image forming mechanism 10 and the mechanism control unit 51 of the present embodiment corresponds to an example of the image forming unit referred to in the present invention. The combination of the paper transport mechanism 20 including the reverse transport unit 29, the reverse transport control unit 53, and the transport control unit 52 corresponds to an example of the paper transport unit referred to in the present invention.

  FIG. 5 is a diagram illustrating a state in which the sheet is reversed by the reversing conveyance unit illustrated in FIG.

  FIG. 5 shows in order from part (a) to part (e) how the two sheets P1 and P2 are sequentially processed by the reverse conveyance unit 29. As the reverse conveyance unit 29, only the paper sensor 297 and the reverse roll 296 are schematically shown.

  First, as shown in part (a) of FIG. 5, the preceding paper P <b> 1 is conveyed downward along the paper reversal conveyance path 291 (see FIG. 2) as the reverse roll 296 rotates forward. When the leading end of the paper in the transport direction passes the paper sensor 297, the paper sensor 297 detects the presence of the paper, and the transport control unit 52 (see FIG. 4) confirms that the paper transport is normal and there is no paper jam.

  As shown in part (b) of FIG. 5, when the trailing edge of the paper P1 passes through the paper sensor 297, the paper sensor 297 detects the absence of paper. As a result, it is detected that the trailing edge of the sheet is approaching the reverse roll 296, and the reverse roll 296 stops. Subsequently, as shown in part (c), the reversing roll 296 moves a predetermined distance in the direction of the rotation axis with the paper sandwiched therebetween, and moves the paper in the width direction to a position where detection of the presence of the paper by the paper sensor is avoided. . Subsequently, as shown in part (d), the reverse roll 296 rotates in the reverse direction and transports the paper P1 in reverse. At this time, the subsequent paper P2 is conveyed downward along the paper reversal conveyance path 291. The sheets P1 and P2 have overlapping portions, but these overlapping portions avoid the position of the sheet sensor 297. Therefore, as shown in parts (d) and (e), the paper sensor 297 detects the presence of paper when the leading edge of the succeeding paper P2 passes through the paper sensor 297 without being obstructed by the preceding paper P1, It can be confirmed that the subsequent paper P2 is normally conveyed and that there is no paper jam. That is, without waiting for the preceding paper P1 to be transported in reverse to pass the position of the paper sensor 297, by detecting the presence of the paper at the leading edge of the subsequent paper P2 transported from the fixing unit, the paper jam can be quickly detected. Can be detected. In addition, in order to detect the presence of a sheet at the leading edge of the succeeding sheet P2, it is not necessary to increase the distance between the preceding sheet P1 and the succeeding sheet P2 in the sheet conveying direction, so that it is possible to suppress a decrease in image formation productivity.

  FIG. 6 is a flowchart for explaining a control process of the reverse conveyance unit shown in FIG.

  Here, the reverse conveyance control process by the control unit 50 will be described with reference to FIGS.

  First, in step S11, the conveyance control unit 52 determines whether or not the paper sensor detects the presence of paper. Here, when the paper sensor 297 does not detect the presence of paper (No), the conveyance control unit 52 determines whether or not a predetermined time for determining a paper jam has elapsed since the fixing by the fixing unit 16 (step). S12). Here, when the predetermined time has elapsed (Yes), the conveyance control unit 52 stops the operation of the sheet conveyance mechanism 20 because the sheet jam occurs downstream in the conveyance direction with respect to the fixing unit 16, and the image forming mechanism. 10 is also stopped (step S13). The image forming apparatus 1 of the present embodiment is configured to detect the presence / absence of a sheet conveyed from the fixing unit 16 at the leading end of the sheet, so that a predetermined time for determining a paper jam is set to a short time. can do. In step S12, if the predetermined time has not elapsed (No), the processing from step S11 is repeated.

  If the paper sensor 297 detects the presence of paper in Step S11 (Yes), the reverse conveyance control unit 53 waits for a predetermined discharge time to elapse for the preceding paper (Step S15: No), and then performs a predetermined discharge. After the elapse of time, the reverse roll 296 is stopped (step S16), and the reverse roll 296 is moved to a predetermined home position (step S17). Then, the reverse conveyance control unit 53 starts normal rotation of the reverse roll 296 (step S19). The sheet is conveyed in the conveyance direction A (see FIG. 2).

  Subsequently, the reverse conveyance control unit 53 waits until the paper sensor 297 detects the absence of paper (step S20: No), and when the paper sensor 297 detects the absence of paper (step S20: Yes), the reverse roll 296 is passed after a predetermined time. (Step S21), the reversing roll 296 is moved in the direction of the rotation axis (step S22), and the reversing roll 296 is driven in reverse (step S23). Accordingly, the reverse roll 296 transports the paper transported to the paper reverse transport path 291 in the opposite direction while avoiding detection of the presence of the paper by the paper sensor 297. In step S23, timing of the time determined in the determination process in step S15 is started. The predetermined discharge time determined in step S15 is set based on the time required for the sheet to leave the reversing roll 296. Among the above processes, the process of moving the reversing roll 296 in the direction of the rotation axis (step S22) is performed after the reversing roll 296 is stopped by the process of step S21 and before the reverse driving is performed by the process of step S23. . For this reason, the sheet nipped by the reversing roll 296 moves in the direction of the rotation axis while avoiding the nipping by the rolls other than the reversing roll 296, for example, the discharge roll 27, the introduction roll 295, or the refeed conveyance roll 31a. The occurrence of twisting and skewing of the paper is suppressed.

  Next, a second embodiment of the present invention will be described.

  In the following description of the second embodiment, the same reference numerals are given to the same elements as those in the embodiments described so far, and differences from the above-described embodiments will be described.

  The paper transport mechanism 20 in the image forming apparatus according to the second embodiment employs a center register system that transports paper with the center position in the width direction of each paper aligned when transporting a plurality of paper sheets having various sizes. It is. In the center registration method, the position of the side edge of the conveyed paper changes according to the paper size.

  FIG. 7 is a schematic configuration diagram illustrating a sheet sensor, a reversing roll, and a peripheral portion thereof in the image forming apparatus according to the second embodiment of the present invention.

  The paper sensor 397 shown in FIG. 7 is movable in the width direction. When the size of the paper transported by the paper transport mechanism 20 is changed, the paper sensor 397 is constant from the side edge position of the changed paper. Move to the home position that keeps the distance.

  FIG. 8 is a block diagram showing a moving mechanism of the paper sensor of FIG.

  The sheet sensor 397 is fixed to a timing belt 3972 stretched around a pair of pulleys 3971. The timing belt 3972 is driven by a motor 3972 and moves. The paper sensor 397 moves in the paper width direction as the timing belt 3972 moves. The motor 3973 is controlled by the reverse conveyance control unit 53 shown in FIG. 4 as a part of the reverse conveyance unit 29. In the second embodiment, specifically, the reverse conveyance control unit 53 obtains the paper size information input from the touch panel 60 by the operation of the operator, drives the motor 3993 based on the paper size information, and the paper sensor 397. Is moved to the home position according to the paper size. For example, when the paper size shown in FIG. 7 is changed from P3 to a larger P4 based on the input paper size information, the paper sensor 397 is indicated by an arrow by a distance that is ½ of the paper width difference. Move in the direction. As a result, the home position of the paper sensor 397 is always located at a constant distance from the side edge regardless of the paper size, so that the paper movement distance by the reverse roll 296 can be made constant. A combination of the pulley 3971, the timing belt 3972, the motor 3973, and the reverse conveyance control unit 53 corresponds to an example of the sensor position adjusting unit according to the present invention.

  Note that the method of obtaining the paper size information by the reverse conveyance control unit 53 is not limited to the touch panel 60, and for example, extracting from the information transmitted from the personal computer 70 (see FIG. 4) accompanying the image signal. Is also possible.

  In the first and second embodiments, the reverse conveyance when the paper is discharged via the reverse discharge path 293 has been described. Here, also in the case of image formation on both sides of the paper, when the paper is reversely conveyed toward the double-sided branch path 294, the paper passes through the reverse discharge path 293 except that the paper is conveyed to the double-sided branch path 294 by a gate (not shown). It is possible to perform reverse conveyance and processing.

  In the image forming apparatus 1 of the present embodiment, the reversing roll 296 is moved in the direction of the rotation axis after the reversing roll 296 stops rotating and before the reversing, but the image forming apparatus of the present invention. However, the present invention is not limited to this, and it is sufficient that the reversing roll moves in the direction of the rotation axis while avoiding the time when the reversing roll is sandwiched between rolls other than the reversing roll. For example, after the paper sensor 297 detects the absence of paper The movement in the direction of the rotation axis may be started, and the movement in the direction of the rotation axis is started after a predetermined time that is scheduled to be sandwiched between rolls other than the reverse roll after the reverse roll starts to rotate backward. Anything that ends is acceptable.

  In the image forming apparatus 1 of the present embodiment, the nip formed by the pair of reversing rolls 296 is not opened, but the present invention is not limited to this. In the present invention, for example, a pair of reversing rolls are configured to be movable to a position where they are separated and abutted with each other, and after the preceding paper being reversed and conveyed is pinched by the discharge roll, the reversing roll is separated and the paper is pinched. At the same time, the succeeding sheet is inserted between the reversing rolls to reduce the interval between the preceding sheet and the succeeding sheet by allowing the preceding sheet and the succeeding sheet to overlap each other on the deeper side of the reversing sheet reversing conveyance path than the reversing roll. The present invention can also be applied to an image forming apparatus.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. It is a schematic block diagram which shows the inversion conveyance unit shown in FIG. 1, and its peripheral part. It is a schematic block diagram which shows the paper sensor shown in FIG. 2, a reversing roll, and its peripheral part. FIG. 2 is a functional block diagram of the image forming apparatus illustrated in FIG. 1. It is a figure explaining a mode that a paper is reversed by the reverse conveyance unit shown in FIG. It is a flowchart explaining the control processing of the reverse conveyance unit shown in FIG. It is a schematic block diagram which shows the paper sensor, the inversion roll, and its periphery part in the image forming apparatus of 2nd Embodiment of this invention. It is a block diagram which shows the moving mechanism of the paper sensor of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Image forming mechanism 16 Fixing unit 20 Paper conveyance mechanism 29 Reverse conveyance unit 50 Control part 291 Paper reverse conveyance path 296 Reverse roll 297,397 Paper sensor 3971 Pulley 3972 Timing belt 31973 Motor A Paper conveyance direction B Reverse conveyance direction R Paper transport path

Claims (4)

An image forming unit that forms an image on the conveyed paper;
A sheet conveying unit that sequentially conveys a plurality of sheets on a sheet conveying path passing through the image forming unit,
The paper transport unit is
A paper reversing conveyance path that is arranged downstream of the image forming unit in the paper conveyance path and that conveys a sheet on which an image is formed in the image forming unit;
A paper sensor disposed on the paper reversal conveyance path for detecting the presence or absence of paper;
A reversing conveyance unit configured to convey the sheet conveyed to the sheet reversing conveyance path in a direction opposite to the direction in which the sheet has been conveyed to the sheet reversing conveyance path while avoiding detection of the presence of the sheet by the sheet sensor; An image forming apparatus comprising:   The reversing conveyance unit is provided with a pair of reversing rolls that are capable of reversing forward and reverse, sending paper to the paper conveying path and feeding paper from the paper reversing conveying path, and the pair of reversing rolls are further movable in the rotation axis direction. 2. The sheet according to claim 1, wherein the sheet is moved in the width direction perpendicular to the sheet conveying direction to a position where detection of the presence of the sheet by the sheet sensor is avoided by moving in the rotation axis direction. Image forming apparatus.   3. The image forming apparatus according to claim 2, further comprising: a sensor position adjustment unit that obtains paper size information representing the size of the paper and moves the paper sensor in the width direction based on the paper size information. The image forming apparatus described.   3. The pair of reversing rolls, wherein the paper sandwiched between the reversing rolls moves in the direction of the rotation axis while avoiding the time when the paper is sandwiched between rolls other than the reversing roll. Image forming apparatus.

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