JP5014283B2 - Sheet conveying apparatus and image forming apparatus having the same - Google Patents

Description

  In the present invention, the presence or absence of a sheet is detected by an optical sensor at a curved portion of a sheet conveyance path that is curved upstream in the sheet conveyance direction with respect to a registration roller that conveys the sheet, and the sheet conveyed by the registration roller is detected. The present invention relates to a sheet conveying apparatus that stops driving the registration roller after a predetermined conveying time has elapsed after detection from detection of sheet presence to detection of sheet absence by the optical sensor, and an image forming apparatus including the sheet conveying apparatus.

  For example, in an electrophotographic image forming apparatus, generally, an electrostatic latent image is formed on the surface of an image carrier such as a photosensitive drum, and the electrostatic latent image on the surface of the image carrier is developed with a developer. The toner image is formed on the surface of the image carrier, and the toner image is transferred from the image carrier to the sheet while the plain paper or OHP sheet is sandwiched and conveyed in the nip area between the image carrier and the transfer member. Is heated and pressurized to fix the toner image on the sheet.

  In such an image forming apparatus, a sheet conveying apparatus is incorporated, and the sheet is pulled out from a sheet feeding unit such as a sheet feeding tray and conveyed by the sheet conveying apparatus. In this sheet conveying apparatus, it is most preferable that the sheet conveying path is a straight line. However, the sheet conveying path cannot be kept linear due to the arrangement of components such as a paper feed tray and a photosensitive drum. Often curved at points.

  In addition, a registration roller (also referred to as a PS (Paper Stop) roller) is provided upstream of the nip area between the image carrier and the transfer member in the sheet conveyance direction in the conveyance path of the sheet conveyance device. Apply the leading edge of the sheet (downstream end in the sheet conveyance direction) to the registration roller, bend the sheet, and align the leading edge of the sheet in parallel with the registration roller by the elastic force of the sheet. It is transported to. This prevents the sheet from being inclined and passing through the nip region, so that the toner image is not transferred obliquely to the sheet.

  On the other hand, after the sheet has passed the registration roller, it is necessary to stop the rotational drive to the registration roller before the next sheet arrives at the registration roller in order to bend the leading edge of the next sheet against the registration roller. However, the rotation of the registration rollers is often stopped by detecting the presence or absence of a sheet upstream of the registration rollers in the sheet conveyance direction. An optical sensor may be used as means for detecting the presence or absence of the sheet. In a sheet conveying apparatus using an optical sensor, after a predetermined conveying time has elapsed after detection by the optical sensor at the trailing edge of the sheet (upstream side end in the sheet conveying direction), the rotational driving to the registration rollers is temporarily stopped and the next It prepares for sheet conveyance. The predetermined conveyance time is a time required for the trailing edge of the sheet to pass through at least the conveyance distance after detection from the trailing edge detection position of the sheet to the registration roller. From the conveyance distance after detection and the conveyance speed of the sheet, It can be obtained in advance.

  By the way, in the sheet conveying apparatus having a sheet conveying path that is curved on the upstream side in the sheet conveying direction with respect to the registration roller, when detecting the presence or absence of the sheet conveyed by the registration roller, If the sheet characteristics such as the stiffness of the sheet and the optical characteristics are different, the detection timing by the optical sensor at the rear end of the sheet may be different, which is not preferable. In this regard, as an example of an optical sensor, a reflection type optical sensor that detects the presence or absence of a sheet based on the reflected light reflected from the sheet by irradiating the conveyed sheet with reference to FIG. explain.

  FIG. 6 is a diagram for explaining inconveniences when the reflective optical sensor 102 is used in a conventional sheet conveying apparatus having a sheet conveying path S that is curved on the upstream side in the sheet conveying direction of the registration rollers. . FIG. 6A shows a detection state by the reflection type optical sensor 102 when the sheet Q1 having the first sheet characteristic, which is plain paper, is conveyed. FIG. The detection state by the reflective optical sensor 102 when the sheet Q2 having the second sheet characteristic which is a strong OHP sheet is conveyed is shown.

  The conventional sheet conveying apparatus shown in FIG. 6 has a registration roller 101 that conveys the sheets Q1 and Q2, and a bending portion 71 that curves on the upstream side of the registration roller 101 in the sheet conveyance direction (arrow X ′ direction in the figure). And a reflection type optical sensor 102 for detecting the presence or absence of the sheets Q1 and Q2 at the curved portion 71 of the sheet conveyance path S, and the sheets Q1 and Q2 conveyed by the registration rollers 101 are provided. After a predetermined conveyance time elapses after detection from the detection of the presence of the sheet by the reflection type optical sensor 102 to the detection of the absence of the sheet, the rotational drive to the registration roller 101 is temporarily stopped to prepare for the next sheet conveyance. In this sheet conveying apparatus, it is regarded as the rear ends Q1 'and Q2' of the sheets Q1 and Q2 by monitoring that the reflected lights R1 and R2 incident by the reflective optical sensor 102 are no longer detected.

  The registration roller 101 conveys the sheets Q1 and Q2 by being rotationally driven around the axis in the sheet conveyance direction X while sandwiching the sheets Q1 and Q2 between the opposed rollers (here, driven rollers) 105. It is like that.

  The reflective optical sensor 102 is provided outside the curved portion 71 of the sheet conveyance path S, and includes a light emitting unit 102a including a shipping element that radiates the emitted light L to the sheets Q1 and Q2 conveyed by the registration rollers 101. And a light receiving portion 102b including a light receiving element for receiving the reflected lights R1 and R2 reflected from the sheets Q1 and Q2.

  In the conventional sheet conveying apparatus configured as described above, as shown in FIG. 6A, in the conveying operation of the plain paper Q1, the rear end Q1 of the plain paper Q1 that passes through the light irradiation region of the reflective photosensor 102. And the rear end Q2 'of the OHP sheet Q2 that passes through the light irradiation area of the reflective optical sensor 102 in the transport operation of the OHP sheet Q2, as shown in FIG. The detection timing by the sensor 102 to be regarded is different.

  Specifically, the light L is emitted from the light emitting portion 102a to the plain paper Q1 to the rear end Q1 ′ (see FIG. 6A), and the incident direction of the reflected light R1 reflected from the plain paper Q1 to the light receiving portion 102b is substantially the same. Although it is constant, even if the emitted light L is irradiated from the light emitting portion 102a to the OHP sheet Q2 toward the rear end Q2 ′ (see FIG. 6B), the back end is stronger than the plain paper Q1. Since Q2 ′ is likely to jump, the emitted light L passes through the OHP sheet Q2 (see L ′ in FIG. 6B), or the incident direction of the reflected light R2 reflected from the OHP sheet Q2 to the light receiving unit 102b is different. To do. Then, since the OHP sheet Q2 does not enter the reflected light R2 from the OHP sheet Q2 before the rear end Q2 ′ (on the downstream side in the sheet conveying direction X ′), the reflective optical sensor 102 If it passes through the trailing edge Q2 'before passing through the trailing edge Q2' of the sheet Q2, it will be erroneously detected (detected at a timing earlier than the detection timing of the plain paper Q1).

  FIG. 7 shows the detection timing of the sheets Q1 and Q2 by the reflection type optical sensor 102 of the conventional sheet conveying apparatus, the start / stop timing of rotation driving to the registration roller 101, and the conveyance timing of the sheets Q1 and Q2 by the registration roller 101. It is a timing chart. FIG. 7A shows a timing chart when the plain paper Q1 is conveyed, and FIG. 7B shows a timing chart when the OHP sheet Q2 is conveyed. In FIG. 7, a symbol Ts indicates a predetermined conveyance time from when the reflection type optical sensor 102 detects a change from sheet presence detection to sheet absence detection until the rotational drive to the registration roller 101 stops. Yes. “Sensor ON” or “Sensor OFF” in the figure indicates the “present detection state” or “absence detection state” of the sheets Q1 and Q2, respectively, and “registration roller ON” or “registration roller OFF” in the figure. "Is the" driving state "or" driving stop state "for the registration rollers, respectively. In the figure," sheet conveyance ON "or" sheet conveyance OFF "is that the sheets Q1 and Q2 are" conveyed "by the registration rollers 101, respectively. "A state that is being transported" or "a state that is not being transported". The same applies to FIG. 4 described later.

  When the plain paper Q1 is transported in the conventional sheet transport apparatus, as shown in FIG. 7A, after the plain paper Q1 is transported by the registration roller 101 (the trailing edge Q1 ′ of the plain paper Q1 is After passing the registration roller 101, the rotational drive to the registration roller is stopped (see α1 in the figure). On the other hand, when the OHP sheet Q2 is conveyed, as shown in FIG. 7B, the OHP sheet Q2 is being conveyed by the registration roller 101 (the rear end Q2 ′ of the OHP sheet Q2 is the registration roller 101). Before passing), the rotational drive to the registration roller stops (see α2 in the figure).

  As described above, in the conventional sheet conveying apparatus, when an erroneous detection of the reflection type optical sensor 102 occurs, the rear end of the OHP sheet Q2 is in spite of the state in which the OHP sheet Q2 is conveyed by the registration roller 101. It is determined that Q2 ′ has passed the registration roller 101, and the drive to the registration roller 101 is stopped in a state where the OHP sheet Q2 is conveyed to the registration roller 101. At this time, if the OHP sheet Q2 has arrived at the nip area between the image carrier and the transfer member, the OHP sheet Q2 forcibly rotates the registration roller 101 whose driving is stopped while the OHP sheet Q2 is being conveyed. As a result, since the transport load is applied to the OHP sheet Q2, the OHP sheet Q2 is pulled, which may cause image defects such as transfer displacement.

  On the other hand, the following Patent Document 1 discloses a configuration in which an optical axis of a transmissive optical sensor is arranged at a predetermined angle with respect to a sheet conveying surface. Even when applied to a sheet conveying apparatus instead of the sensor, the angle of the optical axis with respect to the sheet conveying surface of the transmissive optical sensor varies depending on characteristics such as the waist of the sheet. Similar to the sheet conveying apparatus, erroneous detection of the trailing edge of the sheet may occur, leading to image defects such as transfer misalignment.

In addition, such inconvenience is caused when the detection by the optical sensor is performed in the bending forming portion (see reference numeral 75 in FIG. 6) for surely bending the sheet so that the leading end of the sheet is aligned in parallel with the registration roller. Especially noticeable.
JP-A-6-87550

  Therefore, in the present invention, the presence or absence of a sheet is detected by an optical sensor at a curved portion of the sheet conveyance path that is curved upstream of the registration roller that conveys the sheet, and the sheet is conveyed by the registration roller. A sheet conveying device that stops driving the registration roller after a predetermined conveyance time has elapsed since the detection of the presence of the sheet by the optical sensor to detection of the absence of the sheet, and the sheet is conveyed by the registration roller. An object of the present invention is to provide a sheet conveying apparatus capable of preventing the driving of the registration rollers from being stopped in a state where the registration roller is stopped, and an image forming apparatus including the sheet conveying apparatus.

In order to solve the above problems, the present invention provides a registration roller that conveys a sheet in a predetermined sheet conveyance direction, a sheet conveyance path that has a curved portion that is curved upstream of the registration roller in the sheet conveyance direction, An optical sensor that detects the presence or absence of a sheet at the curved portion of the sheet conveyance path, and a predetermined conveyance after detection from detection of sheet presence to detection of absence of sheet by the optical sensor of the sheet conveyed by the registration roller met sheet conveying apparatus and a sheet conveyance control means for stopping the driving to the registration roller after a time lapse, the sheet wherein the sheet conveying path, bending forming portion of the resist roller for bending the sheet In the vicinity of the upstream side in the conveyance direction, the sheet conveyance path is provided so as to swell in a concave shape toward the outside, and the optical sensor is It is provided in the deflection forming unit, the sheet conveyance control means, wherein the stop timing of the drive of the registration roller, and the plain paper is a sheet of the first sheet properties, stiffness than the sheet of the first sheet characteristic The OHP sheet, which is a strong second sheet characteristic sheet, can be changed to a first sheet for stopping the registration roller after detection from detection of sheet presence to detection of sheet absence by the optical sensor on plain paper. than the transport time, the sheet conveying apparatus according to claim Rukoto delaying the second transport time for stopping the registration roller after sensing the absence sheet detection from the detection there sheets by the optical sensor in OHP sheet And an image forming apparatus including the same.

According to the sheet conveying apparatus and the image forming apparatus according to the present invention, even when the optical sensor erroneously detects the trailing edge of the OHP sheet, the sheet conveying control unit sets the stop timing of driving to the registration rollers . Since the sheet can be changed between plain paper that is a sheet having one sheet characteristic and an OHP sheet that is a sheet having a second sheet characteristic that is stronger than the sheet having the first sheet characteristic, the sheet is conveyed by the registration rollers. In this state, it is possible to prevent the driving of the registration roller from being stopped, thereby avoiding image defects such as transfer misalignment.
Specifically, before the optical sensor passes through the rear end of the OHP sheet, it is erroneously detected that the optical sensor has passed through the rear end (when the detection by the optical sensor is performed in the bending forming portion, the paper becomes particularly prominent. The sheet conveyance control means stops the registration roller after detection from detection of sheet presence to detection of sheet absence by the optical sensor on plain paper even if it is erroneously detected at a timing earlier than the detection timing of By delaying the second conveyance time for stopping the registration roller after the detection from the detection of the presence of the sheet by the optical sensor to the detection of the absence of the sheet in the OHP sheet, than the first conveyance time for the OHP sheet, It is possible to prevent the drive to the registration roller from being stopped while the toner is being conveyed to the registration roller.

  As described above, according to the present invention, the presence or absence of a sheet is detected by the optical sensor at the curved portion of the sheet conveyance path that is curved upstream of the registration roller that conveys the sheet, and the registration roller A sheet conveying apparatus that stops driving the registration roller after a predetermined conveyance time has elapsed after detection from detection of sheet presence by the optical sensor to detection of sheet absence by the optical sensor. Provided is a sheet conveying device that can prevent the drive to the registration roller from being stopped while the sheet is being conveyed, thereby avoiding image defects such as transfer misalignment, and an image forming apparatus including the sheet conveying device. be able to.

  Hereinafter, an embodiment according to the present invention will be described with reference to the drawings. In addition, the following embodiment is an example which actualized this invention, Comprising: The thing of the character which limits the technical scope of this invention is not.

  FIG. 1 is a side view schematically showing an image forming apparatus D to which an embodiment of a sheet conveying apparatus according to the present invention is applied. The image forming apparatus D includes a document reading device B that reads an image of a document, and an image of the document read by the document reading device B or an image received from the outside in color or single color, such as plain paper or OHP. An apparatus main body A for recording and forming.

  In the document reading device B, when the document is set on the document setting tray 41, the pickup roller 44 is pressed against the surface of the document and rotated, the document is pulled out from the tray 41, and the document passes between the suction roller 45 and the separation pad 46. Then, after being separated one by one, it is transported to the transport path 47.

  In this conveyance path 47, the leading edge of the document comes into contact with the registration roller 49, and the leading edge of the document is aligned in parallel with the registration roller 49. Pass through. At this time, the light of the light source of the first scanning unit 53 is irradiated on the surface of the document through the reading glass 52, and the reflected light is incident on the first scanning unit 53 through the reading glass 52. The image is reflected by the mirrors of the second scanning units 53 and 54 and guided to the imaging lens 55, and an image on the surface of the document is formed on a CCD (Charge Coupled Device) 56 by the imaging lens 55. The CCD 56 reads an image on the document surface and outputs image data indicating the image on the document surface. Further, the document is conveyed by the conveyance roller 57 and is discharged to the paper discharge tray 59 via the paper discharge roller 58.

  In addition, it is possible to read a document placed on the platen glass 61. The registration roller 49, the reading guide 51, the paper discharge tray 59, and the like and the members above them form an integrated cover body, and around the axis along the document conveying direction on the back side of the document reading device B It is pivotally supported so that it can be opened and closed. When the upper cover body is opened, the document table glass 61 is released, and a document can be placed on the document table glass 61. When the document is placed and the cover body is closed, the first and second scanning units 53 and 54 are moved in the sub-scanning direction, and the first scanning unit 53 exposes the document surface on the document table glass 61. Reflected light from the document surface is guided to the imaging lens 55 by the first and second scanning units 53 and 54, and an image on the document surface is formed on the CCD 56 by the imaging lens 55. At this time, the first and second scanning units 53 and 54 are moved while maintaining a predetermined speed relationship with each other, and reflection of the document surface → the first and second scanning units 53 and 54 → the imaging lens 55 → the CCD 56 is performed. The positional relationship between the first and second scanning units 53 and 54 is always maintained so that the length of the optical path of the light does not change, and thereby the focus of the image on the original surface on the CCD 56 is always accurately maintained.

  The entire original image read in this way is sent and received as image data to the apparatus main body A of the image forming apparatus D, and the apparatus main body A records the image on a recording sheet.

  On the other hand, the apparatus main body A of the image forming apparatus D includes an exposure apparatus 1, a developing apparatus 2 (2a, 2b, 2c, 2d), a photosensitive drum 3 (3a, 3b, 3c, 3d) acting as an image carrier, and charging. Intermediate transfer belt device 8 including a container 5 (5a, 5b, 5c, 5d), a cleaner device 4 (4a, 4b, 4c, 4d), and an intermediate transfer roller 6 (6a, 6b, 6c, 6d) acting as a transfer portion. A fixing device 12, a sheet conveying device 100, a paper feed tray 10 that functions as a paper feed unit, and a paper discharge tray 15 that functions as a paper discharge unit.

  The image data handled in the apparatus main body A of the image forming apparatus D is data corresponding to a color image using each color of black (K), cyan (C), magenta (M), yellow (Y), or a single color (for example, This corresponds to a monochrome image using (black). Accordingly, the developing device 2 (2a, 2b, 2c, 2d), the photosensitive drum 3 (3a, 3b, 3c, 3d), the charger 5 (5a, 5b, 5c, 5d), and the cleaner device 4 (4a, 4b, 4c, 4d) and four intermediate transfer rollers 6 (6a, 6b, 6c, 6d) are provided so as to form four types of images corresponding to the respective colors. Is associated with black, b with cyan, c with magenta, and d with yellow to form four image stations. Hereinafter, the description will be made with the suffixes a to d omitted.

  The photoconductor drum 3 is disposed at substantially the center in the vertical direction of the apparatus main body A.

  The charger 5 is a charging means for uniformly charging the surface of the photosensitive drum 3 to a predetermined potential. In addition to a contact type roller type or brush type charger, a charger type charger is used. .

  Here, the exposure apparatus 1 is a laser scanning unit (LSU) provided with a laser diode and a reflection mirror, and exposes the surface of the charged photosensitive drum 3 according to image data, and according to the image data on the surface. An electrostatic latent image is formed.

  The developing device 2 develops the electrostatic latent image formed on the photosensitive drum 3 with (K, C, M, Y) toner. The cleaner device 4 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer.

  In addition to the intermediate transfer roller 6, the intermediate transfer belt device 8 disposed above the photosensitive drum 3 includes an intermediate transfer belt 7, an intermediate transfer belt drive roller 21, a driven roller 22, a tension roller 23, and an intermediate transfer belt. A cleaning device 9 is provided.

  Roller members such as the intermediate transfer belt drive roller 21, the intermediate transfer roller 6, the driven roller 22, and the tension roller 23 stretch and support the intermediate transfer belt 7, and the intermediate transfer belt 7 is supported in a predetermined sheet conveyance direction (in the drawing). Move around in the direction of arrow C).

  The intermediate transfer roller 6 is rotatably supported inside the intermediate transfer belt 7 and is pressed against the photosensitive drum 3 via the intermediate transfer belt 7.

  The intermediate transfer belt 7 is provided so as to be in contact with each photoconductive drum 3, and a color toner image (each color is transferred by sequentially superimposing and transferring the toner image on the surface of each photoconductive drum 3 onto the intermediate transfer belt 7. Toner image). Here, the transfer belt 7 is formed in an endless belt shape using a film having a thickness of about 100 μm to 150 μm.

  The transfer of the toner image from the photosensitive drum 3 to the intermediate transfer belt 7 is performed by the intermediate transfer roller 6 that is in pressure contact with the inner side (back surface) of the intermediate transfer belt 7. A high voltage transfer bias (for example, a high voltage having a polarity (+) opposite to the toner charging polarity (−)) is applied to the intermediate transfer roller 6 in order to transfer the toner image. Here, the intermediate transfer roller 6 is a roller based on a metal (for example, stainless steel) shaft having a diameter of 8 to 10 mm and whose surface is covered with a conductive elastic material (for example, EPDM, urethane foam, or the like). With this conductive elastic material, a high voltage can be uniformly applied to the recording sheet.

  The apparatus main body A of the image forming apparatus D further includes a secondary transfer apparatus 11 including a transfer roller 11a that functions as a transfer unit. The transfer roller 11 a is in contact with the outside of the intermediate transfer belt 7.

  As described above, the toner images on the surfaces of the respective photosensitive drums 3 are stacked on the intermediate transfer belt 7 and become a color toner image indicated by the image data. The stacked toner images of the respective colors are transported together with the intermediate transfer belt 7 and transferred onto the recording sheet by the secondary transfer device 11.

  The intermediate transfer belt 7 and the transfer roller 11a of the secondary transfer device 11 are pressed against each other to form a nip region. The transfer roller 11a of the secondary transfer device 11 has a voltage (for example, a polarity (+) opposite to the toner charging polarity (-)) for transferring the toner image of each color on the intermediate transfer belt 7 to the recording sheet. Is applied). Further, in order to constantly obtain the nip region, either the transfer roller 11a of the secondary transfer device 11 or the intermediate transfer belt drive roller 21 is made of a hard material (metal or the like), and the other is a soft material such as an elastic roller. (Elastic rubber roller, foaming resin roller, etc.).

  In addition, the toner image on the intermediate transfer belt 7 may not be completely transferred onto the recording sheet by the secondary transfer device 11, and the toner may remain on the intermediate transfer belt 7. Causes color mixing. Therefore, the residual toner is removed and collected by the intermediate transfer belt cleaning device 9. The intermediate transfer belt cleaning device 9 includes, for example, a cleaning blade that contacts the intermediate transfer belt 7 as a cleaning member, and residual toner can be removed and collected by the cleaning blade. The driven roller 22 supports the intermediate transfer belt 7 from the inner side (back side), and the cleaning blade is in contact with the intermediate transfer belt 7 so as to press it toward the driven roller 22 from the outer side.

  The paper feed tray 10 is a tray for storing recording sheets, and is provided below the image forming unit of the apparatus main body A. A paper discharge tray 15 provided on the upper side of the image forming unit is a tray for placing printed recording sheets face down.

  In addition, the apparatus main body A is provided with a sheet conveying device 100 for sending the recording sheet in the paper feed tray 10 to the paper discharge tray 15 via the secondary transfer device 11 and the fixing device 12. The sheet conveying apparatus 100 has an S-shaped sheet conveying path S, and along the sheet conveying path S, a pickup roller 16, a roller roller 14a, a separation roller 14b, each conveying roller 13, a pre-registration roller 19, and a resist Conveying members such as a roller 101, a fixing device 12, and a paper discharge roller 17 are arranged.

  The pickup roller 16 is a pull-in roller that is provided at the downstream end of the sheet feeding tray 10 in the sheet conveying direction and supplies recording sheets from the sheet feeding tray 10 to the sheet conveying path S one by one. The separating roller 14a passes the recording sheet between the separating roller 14b and conveys it to the sheet conveying path S while separating the recording sheets one by one. Each conveyance roller 13 and the pre-registration roller 19 are small rollers for promoting and assisting the conveyance of the recording sheet. Each conveying roller 13 is provided at a plurality of locations along the sheet conveying path S. The pre-registration roller 19 is provided in the immediate vicinity of the registration roller 101 on the upstream side in the sheet conveyance direction, and conveys the recording sheet to the registration roller 101. The sheet conveyance path S is provided with a registration roller front sheet detection device (not shown) that detects the timing of the leading edge of the recording sheet (the downstream end in the sheet conveyance direction). This pre-registration roller sheet detection device can be provided, for example, in the vicinity of the pre-registration roller 19. The pre-registration roller sheet detection device is connected to the input system of the control unit 104 in order to transmit the leading edge timing signal of the recording sheet to the control unit 104 described later.

  In the stopped state, the registration roller 101 abuts the leading end of the recording sheet that has been conveyed, aligns the leading end of the recording sheet, and performs intermediate transfer in the nip region between the intermediate transfer belt 7 and the secondary transfer device 11. The recording sheet is conveyed in a timely manner in synchronism with the toner image formed on the intermediate transfer belt 7 so that the toner image on the belt 7 is transferred onto the recording sheet. For example, the registration roller 101 moves the recording sheet so that the toner image on the intermediate transfer belt 7 matches the position where the image on the recording sheet is to be formed in the nip region between the intermediate transfer belt 7 and the secondary transfer device 11. Transport. The sheet conveying operation will be described in detail later.

  The fixing device 12 receives the recording sheet on which the toner image is transferred, and conveys the recording sheet by sandwiching the recording sheet between the heat roller 31 and the pressure roller 32.

  The temperature of the heat roller 31 is controlled to be a predetermined fixing temperature, and the recording sheet is thermocompression bonded together with the pressure roller 32 to melt, mix, and press the toner image transferred to the recording sheet. On the other hand, it has a function of heat fixing.

  The recording sheet after fixing the toner images of the respective colors is discharged onto the paper discharge tray 15 by the paper discharge roller 17.

  It is also possible to form a monochrome image using only one of the four image forming stations and transfer the monochrome image to the intermediate transfer belt 7 of the intermediate transfer belt device 8. Similarly to the color image, this monochrome image is also transferred from the intermediate transfer belt 7 to the recording sheet and fixed on the recording sheet.

  In addition, when performing image formation on both the front side and the front side of the recording sheet, the image on the surface of the recording sheet is fixed by the fixing device 12, and then the recording sheet is discharged on the sheet conveying path S in the sheet discharge roller 17. In the middle of the conveyance, the paper discharge roller 17 is stopped and then reversely rotated, the recording sheet is passed through the reversing path Sr, the recording sheet is reversed, and the recording sheet is guided again to the registration roller 101. Similarly to the front surface of the recording sheet, an image is recorded and fixed on the back surface of the recording sheet, and the recording sheet is discharged to the paper discharge tray 15.

  By the way, a curved portion 71 in which the sheet conveyance path S is curved with a predetermined curvature is formed upstream of the registration rollers 101 in the sheet conveyance direction.

  2 is a cross-sectional view schematically showing the vicinity of the curved portion 71 of the sheet conveying path S in the sheet conveying apparatus 100 shown in FIG.

  As shown in FIG. 2, the curved portion 71 of the sheet conveyance path S is formed between the outer guide 72 and the inner guide 73, and is upstream of the registration roller 101 in a predetermined sheet conveyance direction (in the direction of the arrow X ′ in the figure). And on the downstream side of the pre-registration roller 19.

  The outer guide 72 is fixed. The inner guide 73 is pivotally supported so as to be swingable about a pivot point 73a along a direction orthogonal to the sheet conveying direction X ′. Due to the weight of the inner guide 73, the inner guide 73 rotates clockwise around the pivot point 73a, the end of the inner guide 73 abuts against the stopper 74, and the clockwise rotation of the inner guide 73 is restricted. An inner guide 73 is positioned. The stopper 74 is fixed at a position where it does not contact or interfere with the recording sheets Q1 and Q2 passing through the bending portion 71 with respect to the apparatus main body A.

  Further, the sheet conveying path S is provided with a bend forming portion (space) 75 for securely bending the recording sheets Q1 and Q2 by contacting the leading ends of the recording sheets Q1 and Q2 in parallel with the registration rollers 101. It has been. The bend forming portion 75 is provided in the vicinity of the upstream side of the registration roller 101 in the sheet conveyance direction X ′ such that the outer guide 72 of the sheet conveyance path S swells in a concave shape when viewed from the cross section (as viewed from the cross section). Yes. In other words, the width of the sheet conveyance path S is widened so that the recording sheets Q1 and Q2 that have been bent against the registration roller 101 in a stopped state are accommodated in the vicinity of the upstream side of the registration roller 101 in the sheet conveyance direction X ′. The bending formation part 75 which becomes is provided. The bending forming portion 75 is formed by curving and denting the guide 76 of the sheet conveying path S.

  A reflection type optical sensor 102 that is an example of an optical sensor is provided outside the deflection forming portion 75. In addition, the deflection forming unit 75 irradiates the light Q emitted from the reflective optical sensor 102 to the sheets Q1 and Q2, and receives the reflected light R1 and R2 from the sheets Q1 and Q2 to the reflective optical sensor 102. A light transmissive window (not shown) is provided.

  FIG. 3 is a system block diagram of a control system of the image forming apparatus D. The image forming apparatus D further includes a control unit 104.

  As shown in FIG. 3, the control unit 104 includes a processing device 104a such as a CPU and a storage unit 104b including a memory such as a ROM and a RAM. Specifically, in the image forming apparatus D, the processing device 104a of the control unit 104 loads a control program stored in advance in the ROM of the storage unit 104b onto the RAM of the storage unit 104b and executes it to execute various components. It comes to control.

  The control unit 104 also functions as a sheet conveyance control unit of the sheet conveyance apparatus 100 according to the embodiment of the present invention. For example, the control unit 104, based on the leading edge timing signal of the recording sheets Q1, Q2 from the registration roller front sheet detecting device (not shown), after a predetermined time has passed since the detection of the leading edges of the recording sheets Q1, Q2 (that is, in the stopped state). The rotation of the pre-registration roller 19 is stopped at the timing when the recording sheets Q1 and Q2 that have struck the registration roller 101 are appropriately bent by the bending forming portion 75, and after a predetermined time has elapsed (that is, in the stopped state). The registration roller 101 is driven to rotate (at an image formation timing in which the recording sheets Q1 and Q2 in a state of being bent with the leading end abutting against the registration roller 101 are synchronized with the toner image formed on the intermediate transfer belt 7). Yes.

A sheet conveying apparatus 100 according to an embodiment of the present invention drives a registration roller 101, a sheet conveyance path S, a reflective optical sensor 102, and a registration roller 101 to rotate the registration roller 101 in the sheet conveyance direction X. And a control unit 104 (an example of a sheet conveyance control unit). The drive unit 103 is electrically connected to the output system of the control unit 104 so that an operation signal can be input, and is driven when the operation signal is input. The reflective optical sensor 102 and the like are the same as those of the above-described conventional sheet conveying device shown in FIG.

  In the present embodiment, the control unit 104 drives the registration roller 101 to rotate by the driving unit 103, and sets the recording sheets Q1 and Q2 conveyed by the registration roller 101 to the sheet presence state by the reflective optical sensor 102. The conveyance time from the detection (after the detection that the recording sheets Q1, Q2 are regarded as the trailing ends Q1 ′, Q2 ′) from the detection of the presence of the sheet to the detection of the absence of the sheet is performed. After the passage of the changed conveyance time (for example, the first conveyance time Ts1 in the recording sheet Q1 having the first sheet characteristic or the second conveyance time Ts2 in the recording sheet Q2 having the second sheet characteristic). The drive unit 103 is configured to temporarily stop the rotation of the registration roller 101 and prepare for the next sheet conveyance.

  Here, the recording sheet Q1 having the first sheet characteristic is a plain paper, and the recording sheet Q2 having the second sheet characteristic is an OHP sheet that is stiffer than the plain paper.

  FIG. 4 shows the detection timing of the recording sheets Q1 and Q2 by the reflection type optical sensor 102 of the sheet conveying apparatus 100 according to the embodiment of the present invention, the start / stop timing of the rotational drive to the registration roller 101, and the recording sheet by the registration roller 101. It is a timing chart which shows the conveyance timing of Q1, Q2. FIG. 4A shows a timing chart when the plain paper Q1 is conveyed, and FIG. 4B shows a timing chart when the OHP sheet Q2 is conveyed.

  The first transport time Ts1 for the plain paper Q1 shown in FIG. 4A is preset by the following calculation formula (1).

[First transport time Ts1] = [Transport distance after detection D] / [Transport speed V] (1)
Here, the post-detection transport distance D (see FIG. 2) is the distance from the detection position P1 of the plain paper Q1 detected by the reflective optical sensor 102 to the nipping position P2 of the registration roller 101 with the opposing roller 105, and the transport speed V Is the sheet conveyance speed.

  The control unit 104 includes a plain paper transport mode for transporting the plain paper Q1 and an OHP transport mode for transporting the OHP sheet Q2, and an OHP transport mode (when a sheet recognition signal corresponding to the OHP sheet is input). The second transport time Ts2 is delayed from the first transport time Ts1 in the plain paper transport mode (when a sheet recognition signal corresponding to plain paper is input).

  Specifically, the second transport time Ts2 for the OHP sheet Q2 shown in FIG. 4B is preset by the following calculation formula (2).

[Second transport time Ts2] = [First transport time Ts1 + Extension time Tr] (2)
Here, the extended time Tr is set to a time equal to or longer than the erroneous detection time Td when the rear end Q2 ′ detection of the OHP sheet Q2 by the reflective optical sensor 102 is detected earlier than the rear end Q1 ′ detection of the plain paper Q1. That is, the relationship of the following relational expression (3) is established.

[Extended time Tr] ≧ [Error detection time Td] (3)
(About processing operation by the control unit 104)
Next, the flow of processing performed by the control unit 104 when trouble occurs in the image forming apparatus D will be described with reference to FIG. FIG. 5 is a flowchart showing the printing operation of the image forming apparatus D.

  As shown in FIG. 5, the image forming apparatus D stands by until a print request is made (step S1). At this time, the registration roller 101 is in a stopped state. Here, when there is a print request (step S1: Yes), a paper feed process is executed to transport the recording sheets Q1, Q2 from the paper feed tray 10 to the sheet transport path S (step S2).

  Next, the leading edges of the recording sheets Q1, Q2 are detected by the registration roller pre-sheet detection device in the vicinity of the registration roller 19 (step S3). The rotation drive to the pre-registration roller 19 is stopped after a lapse of a predetermined time from the detection of the leading ends of the recording sheets Q1 and Q2 (step S4). Next, the process waits until the image formation timing synchronized with the toner image formed on the intermediate transfer belt 7 comes (step S5: No). When the image formation timing comes (step S5: Yes), the registration roller 101 is driven to rotate (step S6), and the image formation process is started (step S7).

  Then, it is determined whether or not it is in the OHP conveyance mode (that is, whether a sheet recognition signal corresponding to the OHP sheet is input or a sheet recognition signal corresponding to plain paper is input) (step S8), and is not in the OHP conveyance mode. In this case (that is, in the case of the plain paper transport mode) (step S8: No), the stop timing of the registration roller 101 is set to the first transport time Ts1 (step S9). On the other hand, when it is the OHP conveyance mode (step S8: Yes), the stop timing of the registration roller 101 is set to the second conveyance time Ts2 (step S10).

  Next, it is determined whether or not the image forming process is finished (step S11). When the image forming process is finished (step S11: Yes), the “sensor” from the reflection type optical sensor 102 in the plain paper transport mode. After detecting the “OFF”, after the first transport time Ts1 set in step S9, and in the case of the OHP transport mode, after detecting “sensor OFF” from the reflective optical sensor 102, the first transport time set in step S10. After two transport times Ts2, the rotational drive to the registration roller 101 is stopped (step S12), and it is determined whether or not there is a printing process for the next recording sheet Q (step S13). If there is a printing process for the next recording sheet Q (step S13: Yes), the process proceeds to step S2. On the other hand, if there is no printing process for the next recording sheet Q (step S13: No), the process ends. To do.

  In the sheet conveying apparatus 100 described above, when conveying the plain paper Q1, as shown in FIG. 4A, after the plain paper Q1 is conveyed by the registration roller 101 (the rear end Q1 of the plain paper Q1). After 'passes through the registration roller 101), the rotational drive to the registration roller 101 stops (see α1 in the figure). On the other hand, when the OHP sheet Q2 is conveyed, as shown in FIG. 4B, the stop timing of the rotational drive to the registration roller 101 in the OHP conveyance mode is set to the registration roller 101 in the plain paper conveyance mode. After the OHP sheet Q2 is conveyed by the registration roller 101 (after the rear end Q2 ′ of the OHP sheet Q2 has passed the registration roller 101) by delaying the rotation drive stop timing by a predetermined extension time Tr, the registration is performed. The rotational drive to the roller can be stopped (see α2 in the figure).

  As described above, according to the sheet conveying apparatus 100 according to the embodiment of the present invention, even when the reflective optical sensor 102 erroneously detects the rear end Q2 ′ of the OHP sheet Q2, the control unit 104 performs registration in the OHP conveying mode. Since the stop timing of the rotational drive to the roller 101 is delayed by a predetermined extension time Tr from the stop timing of the rotational drive to the registration roller 101 in the plain paper transport mode, the OHP sheet Q2 is transported by the registration roller 101. In this state, it is possible to prevent the rotational drive to the registration roller 101 from being stopped, and thus it is possible to prevent image defects such as transfer misalignment.

  Here, as the optical sensor of the sheet conveying apparatus 100 according to the embodiment of the present invention, a reflection type optical sensor is used here, but the invention is not limited thereto, and the present invention is also applicable to a transmission type optical sensor. be able to. Further, the sheet conveying apparatus of the present embodiment is applied to the image forming apparatus main body to convey the recording sheet, but is not limited thereto, and is applied to, for example, a document reading apparatus in the image forming apparatus. The original sheet may be conveyed.

1 is a side view showing an image forming apparatus to which an embodiment of a sheet conveying apparatus of the present invention is applied. FIG. 2 is a cross-sectional view illustrating the vicinity of a curved portion of a sheet conveyance path in the sheet conveyance apparatus of FIG. 1. 2 is a system block diagram of a control system of the image forming apparatus. FIG. FIG. 6 is a timing chart showing recording sheet detection timing by the reflection type optical sensor of the sheet conveying apparatus according to the embodiment of the present invention, start / stop timing of rotation drive to the registration roller, and recording sheet conveyance timing by the registration roller; FIG. 4A is a diagram illustrating a timing chart when transporting plain paper, and FIG. 4B is a diagram illustrating a timing chart when transporting an OHP sheet. 4 is a flowchart illustrating a printing operation of the image forming apparatus. FIG. 6 is a diagram for explaining inconveniences when a reflection type optical sensor is used in a conventional sheet conveying apparatus including a sheet conveying path that is curved upstream in the sheet conveying direction with respect to a registration roller. ) Is a diagram showing a detection state by the reflective optical sensor when a sheet having the first sheet characteristic, which is plain paper, is conveyed, and FIG. It is a figure which shows the detection state by the reflection type optical sensor in the case of conveying the sheet | seat of 2 sheet | seat characteristics. FIG. 9A is a timing chart showing sheet detection timing by a reflection type optical sensor of a conventional sheet conveying apparatus, start / stop timing of rotation driving to a registration roller, and sheet conveyance timing by a registration roller. FIG. FIG. 5B is a diagram illustrating a timing chart in the case of transporting paper, and FIG. 5B is a diagram illustrating a timing chart in the case of transporting an OHP sheet.

Explanation of symbols

71 Bending part 100 Sheet conveying apparatus 101 Registration roller 102 Optical sensor 104 Control part (an example of sheet conveying control means)
D Image forming apparatus Q1 Plain paper (an example of a sheet having a first sheet characteristic)
Q1 ′ Rear edge of plain paper Q2 OHP sheet (an example of a sheet having the second sheet characteristic)
Q2 ′ OHP sheet trailing edge S Sheet transport path Ts1 First transport time Ts2 Second transport time X ′ Sheet transport direction

Claims (2)

A registration roller for conveying a sheet in a predetermined sheet conveying direction;
A sheet conveyance path having a curved portion that is curved upstream of the registration roller in the sheet conveyance direction;
An optical sensor for detecting the presence or absence of a sheet at the curved portion of the sheet conveying path;
A sheet conveyance control unit that stops driving the registration roller after a predetermined conveyance time has elapsed since detection of sheet presence detection by the optical sensor from detection of sheet presence by the optical sensor. It met a sheet conveying apparatus,
In the sheet conveyance path, a deflection forming portion for bending the sheet is provided in the vicinity of the upstream side of the registration roller in the sheet conveyance direction so that the sheet conveyance path swells in a concave shape toward the outside,
The optical sensor is provided in the deflection forming portion,
The sheet conveyance control unit is configured to stop driving the registration rollers at a timing of stopping the plain sheet, which is a sheet having the first sheet characteristic, and a sheet having the second sheet characteristic, which is stronger than the sheet having the first sheet characteristic. The OHP sheet can be changed, and the first transfer time for stopping the registration roller after detection from detection of sheet presence to detection of sheet absence by the optical sensor on plain paper is longer than that on the OHP sheet. sheet transport apparatus according to claim Rukoto delaying the second transport time for stopping the registration roller after sensing the absence sheet detection from the sheet there detected by the optical sensor. An image forming apparatus comprising the sheet conveying device according to claim 1 .

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