JP2006330579A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus preventing unnecessary image formation without adding a sensor. <P>SOLUTION: The image forming apparatus 100 includes: a conveying path 104 extending from a paper feed cassette 101 and used to convey paper to a paper ejection tray 103 via an image forming section 102 used to record a requested image onto one side of the paper; a refeed mechanism 107 disposed downstream of the image forming section in the conveying path 104 and used to refeed conveyed paper to the image forming section 102 after inverting the paper back to front; and a refeed sensor SEN 3 for taking the timing of starting the drive of the refeed mechanism 107. The refeed sensor SEN 3 detects the passage of paper at the position through which only paper with a size suitable for both-sided image formation is passed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms images on both sides of a sheet.

  Conventionally, there is a switchback type image forming apparatus as an image forming apparatus that forms images on both sides of a sheet. The image forming apparatus includes a transport path for transporting a sheet from a paper feed cassette or a manual feed tray to an output tray through an image forming unit that forms an image on one side of the sheet. The paper discharge sensor detects the passage of the paper on which the paper is formed and rotates the paper discharge roller at a predetermined timing to convey the paper to the paper discharge tray side. After the switchback sensor detects the paper passage, the predetermined time At this timing, the switchback mechanism is driven to switch back the paper, and the paper is reversed through the reverse conveyance path and fed back into the conveyance path. Then, an image is formed by the image forming unit on the back side of the sheet sent to the conveyance path, and the sheet discharge sensor detects the passage of the sheet and rotates the sheet discharge roller at a predetermined timing to discharge the sheet. Paper is ejected to the tray. Also, the paper discharge sensor and the switchback sensor may be shared.

  By the way, the conventional image forming apparatus has a limited paper size suitable for double-sided image formation. However, if the paper cassette is selected by mistake or an inappropriate size paper is placed on the manual feed tray, both the paper discharge sensor and the switchback sensor detect the paper near the central position in the paper width direction. Further, there is a problem that paper that is not suitable for double-sided image formation is also detected by the switchback sensor, and an image is erroneously formed on the back side of the paper, resulting in useless image formation. In addition, since the apparatus cannot determine the occurrence of such erroneous image formation, there is a problem in that work time is wasted.

  Therefore, for example, in the image forming apparatus disclosed in Patent Document 1, a plurality of paper size detection sensors detect the width of the paper and determine whether the size is appropriate. In this image forming apparatus, a reference point sensor for detecting one end of a sheet is disposed on a sheet insertion throttle, and a width detection sensor for detecting the other end of the sheet at a position separated from the reference point sensor by a predetermined distance. Are juxtaposed and the width of the paper is detected by detecting whether or not the paper has passed through the detection position of each horizontal width detection sensor, the paper size is determined by the determination unit based on this detection signal, and determined by the comparison unit The paper size is compared with the image formation size. If these comparison results do not match, the paper is discharged without image formation, and a warning is given by the warning unit.

JP-A-8-25318

 However, in the image forming apparatus disclosed in Patent Document 1, since it is necessary to additionally provide a paper size detection sensor in addition to the paper discharge sensor and the switchback sensor, there is a problem in that it is disadvantageous in terms of cost. .

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that can prevent wasteful image formation without providing an additional sensor.

  In order to achieve the above object, an image forming apparatus according to claim 1 is an image that extends from a paper supply unit that supplies paper for recording an image and records a desired image on one side of the paper. Retransmission that is provided in a transport path for transporting paper to the paper discharge tray through the forming section and a transport path downstream from the image forming section, and reverses the transported paper and sends it to the image forming section again. And a resending sensor for detecting the passage of the paper transported through the transport path and for timing when the resending mechanism starts driving, the resending sensor having a size suitable for double-sided image formation. It is characterized in that the passage of the paper is detected at a position where only the paper passes.

  According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the sheet is provided in a transport path on the upstream side of the paper discharge tray and discharges the transported paper to the paper discharge tray. A roller and a paper discharge sensor for detecting the passage of the paper transported through the transport path and timing the paper discharge roller to start rotating, the paper discharge sensor transporting the transport path It is characterized in that the passage of the paper is detected at a position where all the sizes of the paper to be passed through.

  According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, when the double-sided image formation is performed on the paper, the retransmission sensor does not detect the passage of the paper, and the paper is in the discharge tray. When the paper is discharged, the image forming unit stops image formation and the notification unit notifies a warning.

  An image forming apparatus according to a fourth aspect of the invention is the image forming apparatus according to any one of the first to third aspects, wherein the retransmission mechanism moves the paper discharge roller in a direction opposite to a rotation direction in which the paper is discharged. It is characterized in that it is rotated to switch back the paper.

  According to the image forming apparatus of the first aspect, since the re-transmission sensor detects the passage of the sheet at a position where only the sheet of a size suitable for double-sided image formation passes, only the sheet of a size suitable for double-sided image formation is used. Can be reversed and sent back to the image forming unit by the retransmission mechanism. For this reason, paper of a size that is not suitable for double-sided image formation is not sent again to the image forming unit, and image formation is not performed on such paper by the image forming unit, thus preventing wasteful image formation. Can do. Further, since there is no need to provide an additional sensor, there is no disadvantage in cost.

  According to the image forming apparatus of the second aspect, since the paper discharge sensor detects the passage of the sheet at a position where all the sizes of sheets conveyed on the conveyance path pass, all the sheets conveyed on the conveyance path are detected. The paper can be discharged to a paper discharge tray by a paper discharge roller.

  According to the image forming apparatus of the third aspect, when double-sided image formation is performed on a sheet, when the retransmission sensor does not detect the passage of the sheet and the sheet is discharged to the discharge tray, the image forming unit Since image formation is canceled and the notification unit notifies a warning, it is possible to prevent useless image formation. In addition, since it is possible to cause the user or the like to perform double-sided image formation again with a sheet suitable for double-sided image formation by a warning, it is possible to eliminate the waste of work time.

  According to the image forming apparatus of the fourth aspect, since the retransmission mechanism rotates the paper discharge roller in the direction opposite to the rotation direction for discharging the paper to switch back the paper, the paper discharge roller is also used in the retransmission mechanism. As a result, the configuration of the apparatus can be simplified.

  As shown in FIG. 1, the image forming apparatus 100 according to the present embodiment is provided with a paper feed cassette 101 for sequentially supplying paper for recording images on the bottom of the apparatus. An image forming unit 102 is disposed above, and a paper discharge tray 103 is disposed above the image forming unit 102. A transport path 104 for transporting paper from the paper feed cassette 101 to the paper discharge tray 103 extends upward from one end side of the paper feed cassette 101 to the image forming unit 102 and further extends upward. After that, it is formed so as to bend in the horizontal direction and lead to the paper discharge tray 103. Further, the image forming apparatus 100 is provided with a manual feed tray 105 that sequentially supplies sheets placed on the side of the apparatus, and the sheets supplied from the manual feed tray 105 are joined to the conveyance path 104. A manual feed path 106 is formed. As described above, in the image forming apparatus 100, the sheet is conveyed from the paper feed cassette 101 or the manual feed tray 105 to the image forming unit 102, and the image is recorded on the sheet by the image forming unit 102.

  Further, the image forming apparatus 100 is provided with a re-transmission mechanism 107 that reverses the front and back of the transported paper and sends it again to the image forming unit 102 in the transport path 104 downstream of the image forming unit 102. The retransmission mechanism 107 is disposed between the image forming unit 102 and the paper discharge tray 103, and is switched back by the switchback mechanism 108 that switches back the paper conveyed on the conveyance path 104. And a reverse conveying path 109 formed so that the sheet joins the conveying path 104. As described above, in the image forming apparatus 100, when an image is recorded on the other side of the sheet on which the image is recorded on one side by the image forming unit 102, the switchback mechanism 108 passes the reverse conveyance path 109. Then, an image is recorded by the image forming unit 102 on the other side of the sheet conveyed. In the image forming apparatus 100, double-sided image formation is performed only for A4 size paper, and single-sided image formation is A4 size or smaller paper, for example, standard sizes such as A4, B5, A5, B6, or the like. It is suitable for other postcards and letters.

  The paper feed cassette 101 is a box-like shape capable of storing various sizes of paper, and is provided at the bottom of the apparatus so that it can be pulled out, so that paper can be loaded as needed. Inside the paper feed cassette 101, the stacked sheets are regulated so as to be positioned at the center position in the width direction of the sheets, that is, in the direction orthogonal to the sheet transport direction, and a variable (not shown) that prevents oblique feeding. A guide of the type is arranged. In addition, a guide 10 is provided inside the paper feed cassette 101 to hold a predetermined size of paper at the paper feed position. The guide 10 is provided so as to be swingable within a predetermined range around the fulcrum 10a, and its bottom plate is urged upward by an elastic member to hold a plurality of sheets in a stacked state, and at the top thereof. One end of the paper is always positioned at the paper feed position. A paper feed roller 11 and a separation pad 12 are provided at the paper feed position, and the uppermost paper positioned at the paper feed position by the guide 10 is in pressure contact with the paper feed roller 11. By being urged upward by an elastic member (not shown), the separation pad 12 is pressed against the roller surface of the paper feed roller 11, and the sheets passing through the pressed portion are separated and supplied one by one by friction, The paper feed roller 11 rotates while being pressed against the uppermost paper so that the paper is fed into the transport path 104.

  The image forming unit 102 includes a scorotron charger 21, an LED printer head 22, a developing unit 23, a transfer unit 24, and a cleaning device 25 disposed around the photosensitive drum 20, and a downstream side of the photosensitive drum 20. The fixing unit 26 is disposed in the conveyance path 104.

  The photoconductive drum 20 has a photoconductive film formed of an organic photoconductor formed on the surface thereof, and is rotated at a predetermined speed by a motor (not shown). The scorotron charger 21 is of a so-called non-contact corona charging type, and although not shown in detail in the drawing, a discharge wire is disposed at the approximate center of a casing electrode forming a half space, and a photosensitive member. A grid electrode is arranged on the drum 20 side, and a corona discharge is generated when a predetermined voltage is applied to the discharge wire, and the amount of ions generated by the corona discharge is controlled by the grid electrode. It should be noted that other charging devices such as a contact roller charging method may be employed instead of the non-contact corona charging method.

  The LED printer head 22 is a so-called self-light-emitting printer head in which LED arrays are arranged in parallel for the number of recording pixels, and light emitted from the LED array is imaged on the surface of the photosensitive drum 20 by a Selfoc lens array. The surface of the photosensitive drum 20 is selectively exposed to the photosensitive drum 20 based on image information to form an electrostatic latent image on the surface. As the image information, for example, an image of a document read by a reading table that functions as a flat bed scanner (not shown) is transmitted to the LED printer head 22 as an electrical signal. As the exposure device, a scanning optical system using a semiconductor laser in addition to the LED printer head 22 may be employed.

  The developing device 23 includes a supply roller 27, a development roller 28, and a toner container 29. The toner is generated by a difference in bias voltage applied to the supply roller 27 and the development roller 28 from an electric circuit (not shown). The toner in the container 29 is supplied to the developing roller 28 via the supply roller 27. The toner layer formed on the surface of the developing roller 28 is made uniform by pressing the regulating blade 30 to which a predetermined bias voltage is applied. In this way, the developing roller 28 having a uniform toner layer formed on the surface is rotated at a position close to the photosensitive drum 20, and on the developing roller 28 due to a potential difference from the electrostatic latent image on the photosensitive drum 20. The toner moves to the photosensitive drum 20, and a toner image is formed on the surface of the photosensitive drum 20 based on the electrostatic latent image.

  The transfer unit 24 is a transfer roller made of an EPDM foam, and is pressed against the photoconductive drum 20 at a position opposed to the conveyance path 104. When the bias voltage is applied from an electric circuit (not shown), the photoconductor The toner image on the drum 20 is transferred to a sheet. Instead of the contact type conductive roller type, a non-contact type transfer device such as a corona transfer device may be used.

  In the cleaning device 25, a cleaning roller made of an EPDM foam is pressed against the photoconductor drum 20 after transfer, and a constant voltage is applied from an electric circuit (not shown) to remain on the surface of the photoconductor drum 20. The toner and paper dust are removed and the electrostatic latent image is erased. Thereby, the surface of the photosensitive drum 20 is cleaned, and continuous use is possible. As the cleaning device, other contact type methods such as a blade or a non-contact type can be adopted, and a cleaningless type can also be adopted.

  The fixing device 26 fixes the sheet on which the toner image has been transferred by heating and pressing by a heating roller 31 and a pressing roller 32 that are respectively disposed at positions opposed to the conveyance path 104. The surface of the heating roller 31 is maintained at a predetermined temperature by a heater (not shown). A pressure roller 32 is pressed against the heating roller 31 with a predetermined pressure. The sheet on which the toner image has been transferred is nipped between the heating roller 31 and the pressure roller 32 so that the toner on the sheet is melted and fixed.

  A sheet is transported from the paper feed cassette 101 to the image forming unit 102 along a transport path 104, and a sheet on which an image is recorded is transported to a paper discharge tray 103. The transport path 104 is connected to the paper feed cassette 101. A pair of conveying rollers 40 that nip and convey the sheet is provided in the middle thereof. The transport roller 40 is a roller in which an EPDM roller is rotated by transmitting a rotational force from a driving source such as a motor to a roller shaft, and the pair of transport rollers 40 are arranged at opposite positions of the transport path 104. It is disposed so as to be in pressure contact with the roller surface.

  A paper feed sensor SEN1 is provided in the transport path 104 upstream of the pair of transport rollers 40. The paper feed sensor SEN1 is a sensor that detects the leading edge of the paper transported through the transport path 104 and outputs a signal to the control unit 1 (see FIG. 4). As such a paper feed sensor SEN1, a sensor capable of detecting the presence or absence of paper passing at a predetermined detection position is used. For example, various optical sensors such as a reflective photo interrupter are preferably used. . The paper feed sensor SEN1 is provided substantially at the center in the width direction of the paper in the transport path 104, that is, in the direction orthogonal to the paper transport direction, so that paper of all sizes to be transported can be detected. The control unit 1 performs control to rotate the transport roller 40 and operate the image forming unit 102 according to the output from the paper feed sensor SEN1, and specifically, the paper feed sensor SEN1 After receiving a signal indicating that the leading edge of the paper has been detected, the conveying roller 40 is rotated after a lapse of a predetermined time, and the paper is sent to the image forming unit 102 at a predetermined timing, so that a desired image is recorded on the conveyed paper. Control as follows.

  The manual feed tray 105 is capable of carrying a plurality of sheets of various sizes in a stacked state, and is fixed to be inclined slightly in the direction in which the sheets are supplied to the side of the apparatus. A variable guide (not shown) is arranged to prevent the paper stacked on the manual feed tray 105 from being positioned at the center position in the width direction of the paper, that is, in the direction orthogonal to the paper conveyance direction, and to prevent oblique feeding. It is installed. A paper feed roller 51 and a separation pad 52 are provided at the paper feed position on the lower end side of the inclined manual feed tray 105. A separation pad 52 urged upward by an elastic member (not shown) is pressed against the roller surface of the paper feed roller 51, and the paper passing through the pressure contact portion is separated and supplied one by one by friction. The paper 51 is fed into the manual feed path 106 by rotating 51 while being pressed against the uppermost paper. The manual feed path 106 extends from the manual feed tray 105 and is formed so as to join the transport path 104 on the downstream side of the paper feed sensor SEN1.

  A switchback mechanism 108 is disposed in the conveyance path 104 between the image forming unit 102 and the paper discharge tray 103, switches back the paper conveyed through the conveyance path 104, and feeds it to the reverse conveyance path 109. The paper discharge roller 70 disposed at the terminal end of the transport path 104 and rotating in both forward and reverse directions (both in the directions A and B in the figure) and the paper discharge roller 70 are located facing each other across the transport path 104. , A driven roller 71 that rotates following the rotation of the paper discharge roller 70, a turning pawl 72 that is provided at a branch point between the conveyance path 104 and the reverse conveyance path 109, and switches the sheet conveyance path, and the control unit 1 (Refer to FIG. 4).

  The paper discharge roller 70 is a roller in which a roller made of EPDM or silicon rotates when a rotational force from a driving source such as a motor is transmitted to a roller shaft. And transport it. The discharge roller 70 normally rotates in the direction of arrow A, and discharges the sheet that has passed through the image forming unit 102 to a discharge tray 103 provided outside. On the other hand, when the paper surface that has passed through the image forming unit 102 is reversed and supplied to the image forming unit 102 again, such as when performing double-sided image formation, the paper is at a certain position, here FIG. As shown in FIG. 5, when the trailing edge of the sheet is conveyed to the vicinity of the sheet discharge roller 70, the discharge roller 70 rotates in the reverse direction and rotates in the direction of arrow B, and switches the sheet conveyance direction to the reverse conveyance path 109. Transport toward.

  The diverting pawl 72 is a conveyance path switching unit that is provided at a branch point between the conveyance path 104 and the reverse conveyance path 109 and switches the sheet conveyance path, and has a substantially triangular side surface having a tip portion formed at a smooth acute angle. The shape extends in the width direction of the paper. When the sheet is conveyed from the image forming unit 102 to the discharge roller 70 side, as shown in FIG. 1, the reverse conveyance path 109 is blocked by the leading end, and the sheet is transferred from the discharge roller 70 side to the reverse conveyance path 109. When it is retracted, as shown in FIG. 2, an operation of closing the conveyance path 104 with the tip is performed.

  A paper discharge sensor SEN2 is provided in the transport path 104 on the upstream side of the paper discharge roller 70. The paper discharge sensor SEN2 is a sensor that detects the leading edge of the paper transported through the transport path 104 and outputs a signal to the control unit 1 (see FIG. 4). As such a paper discharge sensor SEN2, a sensor capable of detecting the presence or absence of paper passing at a predetermined detection position is used. For example, various optical sensors such as a reflective photo interrupter are preferably used. . As shown in FIG. 3, the paper discharge sensor SEN2 is provided at the approximate center in the width direction of the paper in the transport path 104, that is, in the direction orthogonal to the paper transport direction, so that paper of all sizes being transported can be detected. It has been. Then, the control unit 1 performs control for conveying the sheet conveyed on the conveyance path 104 toward the sheet discharge tray 103 in accordance with the output from the sheet discharge sensor SEN2. Control is performed so that the paper discharge roller 70 is rotated in the forward direction (direction A) after a predetermined time has elapsed since the paper sensor SEN2 received a signal indicating that the leading edge of the paper has been detected.

  The reversal conveyance path 109 is substantially downstream from the branch point of the conveyance path 104 provided with the deflection pawl 72, on the upstream side of the paper feed cassette 101 and on the downstream side of the paper feed sensor SEN1. A plurality of pairs of transport rollers 90 are provided in the middle of the sheet so as to nip and transport the sheet. The transport roller 90 is a roller in which an EPDM roller is rotated by transmitting a rotational force from a driving source such as a motor to a roller shaft, and the pair of transport rollers 90 are mutually opposed to the opposite positions of the reverse transport path 109. It is arrange | positioned so that it may press-contact with the roller surface of this.

  A switchback sensor (retransmission sensor) SEN3 is provided in the transport path 104 on the downstream side of the paper discharge sensor SEN2. The switchback sensor SEN3 is a sensor that detects the trailing edge of the sheet conveyed on the conveyance path 104 and outputs a signal to the control unit 1 (see FIG. 4). As such a switchback sensor SEN3, a sensor capable of detecting the presence or absence of paper passing at a predetermined detection position is used, and for example, various optical sensors such as a reflective photo interrupter are preferably used. . As shown in FIG. 3, the switchback sensor SEN3 detects the width of the conveyance path 104 so that only the A4 size sheet can be detected among the sheets conveyed. A4 size paper in the direction, that is, the direction orthogonal to the paper transport direction passes, and is provided at a position where paper less than A4 size does not pass. The control unit 1 performs control for feeding the sheet toward the reverse conveyance path 109 in accordance with an output from the switchback sensor SEN3 and an instruction input from the operation unit 5 (see FIG. 4). Specifically, after a predetermined time elapses after the switchback sensor SEN3 receives a signal indicating that the trailing edge of the sheet has been detected, the discharge roller 70 is rotated in the reverse direction (direction B), and the turning pawl 72 is moved. An operation is performed so that the conveyance path 104 is blocked by the leading end, and the sheet is fed toward the reverse conveyance path 109. Further, control is performed so that the conveyance rollers 90 arranged in the reversal conveyance path 109 are rotated to rejoin the sheet to the conveyance path 104. The predetermined time needs to be shorter than the time required from when the switchback sensor SEN3 detects the trailing edge of the paper until the trailing edge of the paper passes the paper discharge roller 70. The sheet that has been carried into the conveyance path 104 again has its front and back direction reversed, that is, the surface opposite to the surface (front surface) on which the image has already been formed (back surface) is the photoreceptor of the image forming unit 102. The drum 20 is conveyed so as to be in contact with the surface of the drum 20, and an image is formed on this surface by the image forming unit 102.

  FIG. 4 is a block diagram showing an electrical configuration of the image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 includes a control unit (MPU: Microprocessing Unit) 1, a ROM (Read Only Memory) 2, a RAM (Random Access Memory) 3, an image memory 4, an operation unit 5, a notification unit 6, the image forming unit 102, The image forming apparatus 100 includes the paper feed roller 40, the paper discharge roller 70, the retransmission mechanism 107, the paper feed SEN1, the paper discharge sensor SEN2, and the switchback sensor SEN3. The bus 7 is communicably connected.

  The control unit 1 is connected to each unit constituting the image forming apparatus 100 via the bus 7 and controls processing operations of these units. The ROM 2 is a part that stores various programs necessary for the operation of the image forming apparatus 100. The RAM 3 is a part that stores various data such as setting information and operation information used for processing operations of the image forming apparatus 100 in a readable and writable state. The image memory 4 is a part that temporarily stores image data of an image formed in the image forming unit 102. That is, when the image forming apparatus 100 according to the present embodiment is used in a copying machine, image data read by an image reading apparatus (not shown) having a CCD or the like is used in a facsimile machine. The image data received by facsimile is stored in the case of image data received from a computer when used in a printer. The operation unit 5 includes various operation keys linked with the notification unit 6 such as a start key for instructing start of image formation, a numeric keypad for inputting the number of copies, a cursor key for performing various settings, and the like. The notification unit 6 is a part for notifying the user of various information such as an operation state and a setting state of the image forming apparatus 100, and displays a liquid crystal display panel that displays characters, figures, and the like by turning on or off. An LED lamp, a speaker that emits a predetermined warning sound and the like to notify the user are provided.

  Hereinafter, in the image forming apparatus 100 according to the present embodiment, the processing operation of each unit of the image forming apparatus 100 when a setting for performing double-sided image formation on a sheet is input from the operation unit 5 will be described with reference to FIG. explain. The processing operation in each part of the image forming apparatus 100 is performed according to the control command of the control unit 1.

  When a setting for performing double-sided image formation on a sheet is input from the operation unit 5 (S1: YES), the control unit 1 first performs a paper feed cassette 101 or manual feed based on the setting input from the operation unit 5. One sheet is fed from the tray 105 into the conveyance path 104. When the leading edge of the paper fed into the transport path 104 passes the detection position of the paper feed sensor SEN1, the paper feed sensor SEN1 outputs a detection signal to the control unit 1. Upon receiving the detection signal, the control unit 1 rotates the transport roller 40 after a predetermined time has elapsed after receiving the detection signal, and feeds the sheet to the image forming unit 102 at a predetermined timing. An image based on the setting input from is formed on one surface (front surface) of the sheet (S2).

  The sheet on which the image is formed on the front side is further conveyed toward the discharge tray 103 side along the conveyance path 104. When the leading edge of the paper passes the detection position of the paper discharge sensor SEN2, the paper discharge sensor SEN2 outputs a detection signal to the control unit 1 (S3: YES). Receiving the detection signal, the control unit 1 rotates the paper discharge roller 70 in the forward direction (A direction) after a predetermined time has elapsed after receiving the detection signal, and conveys the paper toward the paper discharge tray 103 (S4). . Thereafter, when the trailing edge of the sheet passes the detection position of the switchback sensor SEN3 and the switchback sensor SEN3 outputs a detection signal to the control unit 1 (S5: YES), the control unit 1 that has received the detection signal The retransmission mechanism 107 starts to be driven after a predetermined time has elapsed since the detection signal was received. Specifically, the control unit 1 rotates the paper discharge roller 70 in the reverse direction (B direction) (S6), reverses the paper and transports it toward the reverse transport path 109, and further changes the direction pawl 72. Is moved so as to block the conveyance path 104 by the leading end, and the conveyance roller 90 is rotated to reverse the front and back directions of the sheet to the conveyance path 104 via the reverse conveyance path 109 (S7). Then, an image based on the setting input from the operation unit 5 by the image forming unit 102 is formed on the other side (rear side) of the sheet that has been brought into the transport path 104 again, and the double-sided image formation is completed ( S8). Thereafter, when the leading edge of the paper passes the detection position of the paper discharge sensor SEN2, the paper discharge sensor SEN2 outputs a detection signal to the control unit 1 (S9: YES), and after the control unit 1 receives the detection signal. After a predetermined time has elapsed, the paper discharge roller 70 is rotated in the forward direction (A direction) (S10), and the paper is discharged onto the paper discharge tray 103 (S11).

  On the other hand, a sheet with an image formed on the surface is conveyed toward the sheet discharge tray 103 by the sheet discharge roller 70, and the rear end of the sheet does not pass the detection position of the switchback sensor SEN3. When the detection signal is not output to the control unit 1 (S5: NO), the sheet is directly discharged to the discharge tray 103 by the discharge roller 70 (S12). However, as described above, because the size of the paper has become a size suitable for double-sided image formation in the image forming apparatus 100 regardless of the setting for performing double-sided image formation on the paper from the operation unit 5. The image is formed only on the front surface and the paper is discharged. Therefore, contrary to the setting input from the operation unit 5, information indicating that double-sided image formation has not been performed is notified by the notification unit 6 (S13). For example, a warning sound is emitted from a speaker and a message such as “Please select the correct size paper” is displayed on the liquid crystal display panel.

  In this way, the paper discharge sensor SEN2 and the switchback sensor SEN3 detect the passage of the paper without providing an additional sensor as to whether or not the paper has a size suitable for double-sided image formation in the image forming apparatus 100. This can be determined by making the appropriate position. For this reason, it is possible to prevent a useless image from being formed on the back surface of a sheet having a size unsuitable for double-sided image formation. In addition, by notifying the user that the paper is not suitable for double-sided image formation, it is possible to select the correct paper and perform double-sided image formation again, thus eliminating wasted work time. be able to.

  If a setting for performing double-sided image formation on the sheet is input from the operation unit 5 (S1: YES), the sheet is not moved to the detection position of the switchback sensor SEN3 without forming an image on the surface of the sheet. When the sheet is conveyed and the trailing edge of the sheet passes the detection position of the switchback sensor SEN3 and the switchback sensor SEN3 outputs a detection signal to the control unit 1, the control unit 1 that receives the detection signal receives the detection signal. After a predetermined time has elapsed, the driving of the retransmission mechanism 107 is started, the paper discharge roller 70 is rotated in the reverse direction (direction B), the paper is reversed and conveyed toward the reverse conveyance path 109 side, and the surface of the paper Then, an image is formed by the image forming unit 102. Thereafter, the trailing edge of the sheet further passes the detection position of the switchback sensor SEN3, the switchback sensor SEN3 outputs a detection signal to the control unit 1, and the control unit 1 that receives the detection signal receives the detection signal. After a predetermined time has elapsed, the driving of the retransmission mechanism 107 is started, the paper discharge roller 70 is rotated in the reverse direction (direction B), the paper is reversed and conveyed toward the reverse conveyance path 109, and the back surface of the paper After the image is formed by the image forming unit 102, it may be discharged onto the discharge tray 103 by the discharge roller 70.

  As described above, since it is possible to determine whether or not the size of the paper is suitable for double-sided image formation in the image forming apparatus 100 before the image is formed on the paper, the size of paper that is not suitable for double-sided image formation. It is possible to prevent unnecessary images from being formed.

  Note that the configuration of the image forming apparatus 100 shown in the present embodiment is merely an example, and the number of transport rollers 40 and 90 is appropriately increased according to the distance between the transport path 104 and the reverse transport path 109, or the image forming unit 102. It goes without saying that the design can be appropriately changed within a range not departing from the gist of the present invention, such as changing the configuration to another known configuration. For example, in addition to the switchback mechanism 108 that rotates the paper discharge roller 70 in the reverse direction (B direction) to switch back the paper, a roller that rotates in the B direction is provided separately from the paper discharge roller 70. May be used to switch back the paper. Alternatively, the paper feed sensor SEN1 may detect the passage of the leading edge and the trailing edge of the sheet, and determine the length of the sheet in the conveyance direction from the elapsed time at the time of detection. As a result, not only the width in the direction perpendicular to the paper conveyance direction but also the length in the conveyance direction is switched back to form an image on the back side of the paper. It may be.

1 is a schematic diagram illustrating a configuration of an image forming apparatus 100 according to an embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a configuration of the image forming apparatus 100 in a state where a sheet is switched back. FIG. 6 is a schematic diagram illustrating detection positions of a paper discharge sensor SEN2 and a switchback sensor SEN3. 2 is a block diagram showing an electrical configuration of the image forming apparatus 100. FIG. 3 is a flowchart showing processing operations of the image forming apparatus 100.

Explanation of symbols

70 Paper discharge roller 100 Image forming apparatus 101 Paper feed cassette (paper supply unit)
102 Image forming unit 103 Paper discharge tray 104 Transport path 105 Manual feed tray (paper supply unit)
107 Retransmission mechanism SEN2 Paper discharge sensor SEN3 Switchback sensor (Retransmission sensor)

Claims (4)

A conveyance path that extends from a sheet supply unit that supplies a sheet for recording an image, and conveys the sheet to a paper discharge tray via an image forming unit that records a desired image on one side of the sheet;
A resending mechanism that is provided in a transport path downstream from the image forming unit, reverses the front and back surfaces of the transported paper, and sends the paper again to the image forming unit;
A retransmission sensor for detecting the passage of the sheet conveyed through the conveyance path and for timing when the retransmission mechanism starts driving;
And the retransmission sensor detects passage of paper at a position where only paper of a size suitable for double-sided image formation passes.   A paper discharge roller provided in a transport path on the upstream side of the paper discharge tray and configured to detect the passage of the paper transported through the transport path; A paper discharge sensor for timing the start of rotation, and the paper discharge sensor detects the passage of the paper at a position where all the sizes of paper transported through the transport path pass. The image forming apparatus according to claim 1.   When double-sided image formation is performed on a sheet, the retransmission sensor does not detect the passage of the sheet, and when the sheet is discharged to the discharge tray, the image forming unit stops image formation and the notification unit issues a warning. The image forming apparatus according to claim 2, wherein notification is provided.   4. The image forming apparatus according to claim 1, wherein the retransmission mechanism rotates the paper discharge roller in a direction opposite to a rotation direction in which the paper is discharged to switch back the paper. 5. .

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