JP5721871B2 - Sheet conveying apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus, and more particularly to an apparatus including a detection unit that detects a sheet.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a printer or a copying machine, a sheet is fed from a sheet supporting unit such as a sheet feeding cassette or a sheet feeding tray by a feeding roller, and then the sheet is provided in the sheet conveying path. It is transported downstream by the transport device. A detecting means is arranged in the sheet conveyance path so as to detect the position of the leading edge of the sheet.

  Here, when such a detection unit is arranged, in order to stabilize the detection of the detection unit, for example, a rib shape is provided in the sheet conveyance path in which the detection unit is arranged, and the sheet is curved in the sheet conveyance direction. There is one that is adapted to contact the sensor arm (see Patent Document 1).

  FIG. 22 is a diagram illustrating a configuration of a conveyance path of a conventional image forming apparatus in which a rib shape is provided in a sheet conveyance path in which such a detection unit is arranged. In this image forming apparatus, a detecting unit 104 is arranged to detect the sheet P passing through the sheet conveying path 101 formed by the upper guide plate 102 and the lower guide plate 103.

  The detection means 104 includes a sensor 105 and a sensor arm 106 provided on the sensor 105 so as to be swingable via a support shaft. A curved sliding portion 107 is formed at the tip of the sensor arm 106, and the curved sliding portion 107 slides on the sheet P even when the sheet is returned in the direction opposite to the sheet conveying direction indicated by the arrow. In addition, the sensor arm 106 is not caught on the sheet P.

  Here, the sensor 105 is fixedly disposed on the upper guide plate 102, and the curved sliding portion 107 at the tip of the sensor arm 106 supported by the sensor 105 is disposed in contact with the upper surface of the lower guide plate 103. The sensor 105 detects the passage of the sheet P by the swing of the sensor arm 106, or the sensor 105 is disposed in the swing range of the sensor arm 106 with the light emitting element and the light receiving element facing each other. There is one that detects passage of the sheet P by blocking the optical path by movement.

  In FIG. 22, reference numeral 108 denotes a sheet guide portion provided at a position facing the sensor arm 106 of the lower guide plate 103. The sheet guide portion 108 includes parallel rib members 109 and 110 that are provided on both sides of the sensor arm 106 in the width direction orthogonal to the sheet conveyance direction and extend in the sheet conveyance direction and have upper surfaces curved upward. Further, the sheet guide portion 108 is provided at a position facing the curved sliding portion 107 of the sensor arm 106 of the lower guide plate 103 and has a groove portion 111 into which the curved sliding portion 107 of the sensor arm 106 enters.

  In this image forming apparatus, when the sheet P that has moved through the sheet conveyance path 101 reaches the sheet guide portion 108, the sheet P is curved along the upper surfaces of the rib members 109 and 110 that are curved upward. The sheet P is detected by swinging 106.

  On the other hand, in recent years, image forming apparatuses have been demanded to further improve the image quality and performance of output images. For this reason, conventionally, a detection means having an optical sensor for discriminating a sheet in a sheet conveyance path has been required. There is something provided. The detection unit is used to automatically determine the sheet type, and the development condition, transfer condition, and fixing condition are controlled in accordance with the determined type (see Patent Documents 2 and 3).

  Here, in such an image forming apparatus, in order to improve the detection performance of the detection unit, the sheet is sandwiched between a guide installed near the detection unit and a pressure contact unit that presses the sheet against the guide. The sheet flutter is suppressed.

  As described above, in the conventional sheet conveying apparatus and image forming apparatus, in order to increase the detection accuracy of the detection unit, the sheet P is bent toward the sensor arm by the sheet guide unit 108, or the sheet is pressed against the guide by the pressure contact unit. I am doing so.

JP-A-11-255375 JP 2005-345927 A JP 2006-175611 A

  By the way, in the conventional sheet conveying apparatus and the image forming apparatus including the same, for example, by increasing the detection accuracy of the detecting unit by bending the sheet P, the sheet is bent on the lower guide as described above. A rib member is provided. However, when such a rib member is provided, if the used sheet is curled in the sheet conveying direction in advance due to the surrounding environment and storage condition, the position where the sheet tip contacts the sensor arm is in the curled state. It depends on.

  For example, when the leading edge of the sheet is curled upward, the sheet contacts the sensor arm at a position close to the support shaft of the sensor arm, and when the sheet is curled downward, the sheet is sensor arm. Touch the sensor arm on the tip side. If the position where the sheet comes into contact with the sensor arm differs depending on the curl direction as described above, the detection timing of the detection unit becomes unstable, and the detection accuracy of the sheet position is lowered.

  In the case of a thin sheet, when the sheet is placed on a curved rib member, the leading end of the sheet hangs down along the rib member. However, in the case of a thick sheet, the leading end of the sheet does not sag and moves obliquely upward. Become. If the sheet transport posture changes depending on the thickness of the sheet in this way, the position where the sheet contacts the sensor arm changes, and as a result, the detection timing of the detection means becomes unstable, and the detection of the sheet position occurs. Accuracy is lowered.

  As described above, when the position of the sheet in the thickness direction of the sheet is not stable due to the difference between the sheet curl and the sheet type (thickness), the sheet position detection accuracy is lowered. Here, the deterioration of the detection accuracy in the configuration in which the position of the sheet is detected using the sensor arm has been described. For example, even in the case of a detection unit including an optical sensor for determining a sheet, the sheet from the sheet to the detection unit The distance in the thickness direction varies and the detection accuracy decreases. Therefore, as in the case of the detection means using the sensor arm, the position in the thickness direction of the sheet is also stable in the case of the detection means equipped with the optical sensor due to the difference in the sheet curl and the sheet thickness. Otherwise, the detection accuracy will be reduced.

  Even when the sheet is pressed against the guide by pressure contact means on both sides in the width direction of the optical detection means, when the sheet is pressed by the pressure contact means, due to the difference in the posture of the sheet or wrinkles and curls of the sheet itself. The distance from the optical sensor to the sheet varies. And the detection accuracy of a detection means becomes low by such variation in the distance from an optical sensor to a sheet.

  Accordingly, the present invention has been made in view of such a current situation, and an object of the present invention is to provide a sheet conveying apparatus and an image forming apparatus capable of increasing the detection accuracy of a detection unit.

The present invention provides a sheet conveying device, a conveying means for conveying the sheet, a first guide for guiding one surface of the sheet conveyed by said conveying means, the sheet other of which is conveyed by said conveying means A second guide for guiding a surface; an LED provided on one of the first guide and the second guide; and an optical sensor provided on the other of the first guide and the second guide; And detecting means for detecting at least one of the thickness and surface property of the sheet at the detection position , and provided outside the detection position in the width direction perpendicular to the sheet conveyance direction. and the two rotating bodies which are provided on both sides such that said two rotating bodies form the second guide and the nip portion, urging that urges the first guide to the second guide and means, the, before The second guide has a plurality of conveying ribs on the outer side of each nip portion with the two rotating bodies in the width direction, and the height in the thickness direction of the sheets of the plurality of conveying ribs is The height of the sheet is higher than the nip, and the height increases toward the outside in the width direction. When viewed from the downstream side in the sheet conveyance direction, the sheet posture is convex with the detection position as the top. characterized Rukoto is curved sheet to be.

As in the present invention, when the sheet is detected by the detecting means, is curved sheet in the width direction, by Rukoto to reduce variations in the distance between the sensing means and the sheet, it is possible to improve the detection accuracy of the detecting means .

1 is a diagram illustrating a schematic configuration of a sheet printer according to a reference example of the present invention and a laser printer as an example of an image forming apparatus including the same. FIG. 3 is a first diagram illustrating a configuration of a sheet feeding device provided in the laser printer. FIG. 3 is a second diagram illustrating the configuration of the sheet feeding device. FIG. 3 is a first diagram illustrating a configuration of the sheet conveying apparatus. FIG. 3 is a second diagram illustrating the configuration of the sheet conveying apparatus. The figure which shows the state of the sheet | seat at the time of passing the said sheet conveying apparatus. 1 is a diagram illustrating a schematic configuration of a full-color laser beam printer which is an example of an image forming apparatus including a sheet conveying device according to a first embodiment of the present invention. FIG. 4 is a first diagram illustrating a configuration of a conveyance unit that is the sheet conveyance apparatus. FIG. 3 is a second diagram illustrating the configuration of the transport unit. FIG. 4 is a third diagram illustrating the configuration of the transport unit. The figure explaining the state of the sheet | seat at the time of passing the said conveyance unit. FIG. 10 is a diagram illustrating a configuration of a transport unit that is a sheet transport apparatus according to a second embodiment of the present invention. The figure explaining the state of the sheet | seat at the time of passing the said conveyance unit. The figure which shows the structure of the conveyance unit which is a sheet conveying apparatus which concerns on the 3rd Embodiment of this invention. The figure explaining the state of the sheet | seat at the time of passing the said conveyance unit. The figure which shows the structure of the conveyance unit which is a sheet conveying apparatus which concerns on the 4th Embodiment of this invention. The figure explaining the structure of the sheet press-contact unit of the said conveyance unit. FIG. 10 is a first diagram illustrating a configuration of a transport unit that is a sheet transport apparatus according to a fifth embodiment of the present invention. FIG. 3 is a second diagram illustrating the configuration of the transport unit. The figure explaining the structure of the conveyance guide unit of the said conveyance unit. The figure explaining the other structure of the conveyance guide unit of the said conveyance unit. FIG. 10 is a diagram illustrating a configuration of a sheet conveyance path of a conventional image forming apparatus.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram illustrating a schematic configuration of a sheet conveying apparatus according to a reference example of the present invention and a laser printer as an example of an image forming apparatus including the sheet conveying apparatus.

  In FIG. 1, reference numeral 50 denotes a laser printer, and 51 denotes a laser printer main body (hereinafter referred to as an apparatus main body). A sheet feeding device 53 for feeding the sheet P to the image forming unit 52 is provided below the apparatus main body 51. It has been.

  Here, the image forming unit 52 includes a cartridge unit 16 having a photosensitive drum 16a as an image carrier and a laser scanner 11 that exposes the photosensitive drum 16a. In the image formation, the photosensitive drum 16a is exposed by the laser scanner 11 to form a latent image on the surface of the photosensitive drum, and then the latent image is developed, so that the toner on the surface of the photosensitive drum is developed. An image is formed.

  Further, the sheet feeding device 53 includes a sheet feeding cassette 12 that is a sheet stacking unit that is detachably provided on the apparatus main body 51 shown in FIG. Further, a feeding roller 13 shown in FIG. 3 is provided above the sheet feeding cassette 12 and feeds the sheet P stored in the sheet feeding cassette 12.

  As shown in FIG. 1, the sheet feeding cassette 12 is provided with a middle plate 12 a that presses the sheet P against the feeding roller so as to be moved up and down. The middle plate 12a is held by a lifting mechanism (not shown) at a position where the sheet P is pressed against the feeding roller during the sheet feeding operation. Further, the sheet feeding device 53 is provided with a separation pad 13 a as a sheet separating unit that is in pressure contact with the feeding roller 13 and separates the sheet P fed by the feeding roller 13.

The sheet feeding device 53 configured as described above feeds the sheet P stored in the sheet feeding cassette 12 by the feeding roller 13 in parallel with the toner image forming operation of the image forming unit 52 described above. The fed sheet P is separated one by one by a separation unit constituted by a feeding roller 13 and a separation pad 13a, and is sandwiched between a conveyance roller 6 and a conveyance roller 7 provided in the sheet conveyance path 8 to be registered with a pair of registration rollers. 20 is conveyed. In this reference example , a sheet conveying device 54 that conveys a sheet to the image forming unit 52 is configured by the conveying roller 6, the conveying roller 7, and the registration roller pair 20.

  Here, when the sheet P is conveyed from the sheet feeding cassette 12, the registration roller pair 20 is stopped, and the conveyed sheet P contacts the registration roller pair 20 in a stopped state. Then, by contacting the pair of registration rollers 20 stopped in this way, the sheet P is corrected for skew feeding, and at this position, the sheet P stops and waits. Thereafter, when the registration roller pair 20 is rotated and the sheet P is conveyed and is detected by the sheet sensor 15 as detection means, the transfer timing is determined based on the detection of the sheet sensor 15.

  Next, the sheet P is fed to a transfer portion constituted by the photosensitive drum 16a and the transfer roller 8a, and the toner image on the photosensitive drum is transferred to the sheet P when passing through the transfer portion. Further, the sheet P to which the toner image has been transferred is thereafter sent to the fixing unit 17 and is heated and pressed by the fixing unit 17 to fix the toner image. After the image is fixed in this way, the sheet P is discharged to the sheet stacking portion 19 provided on the upper surface of the apparatus main body by the discharge roller pair 18.

  By the way, the sheet conveyance path 8 through which the sheet P fed by the feeding roller 13 passes is constituted by an upper guide 5 and a lower guide 4 which are guide members arranged to face each other. As shown in FIG. 4, a sensor arm 9 that detects the front end of the sheet fed by the feeding roller 13 rotates on the upstream side of the conveyance roller 6 in the sheet conveyance path 8 and the conveyance roller 7 in the sheet conveyance direction. It protrudes freely.

In FIG. 4, reference numeral 10 denotes a light-emitting element and a light-receiving element that are arranged at predetermined positions in the rotation range of the sensor arm 9, and detects the rotation of the sensor arm 9 by blocking the optical path to detect the sheet. It is a sensor that detects passage through the front end. In this reference example , the detection means for detecting the sheet is constituted by a sensor arm 9 and a sensor 10 which are rotatable arm members protruding into the sheet conveyance path.

  When the front end portion of the sheet P fed from the sheet feeding cassette 12 and entered the sheet conveying path 8 contacts the sensor arm 9 and rotates the sensor arm 9, the sensor 10 interrupts the optical path. The passage of the sheet P is detected. After the sensor arm 9 is thus rotated, the sheet P is conveyed to the registration roller pair 20 by the conveyance roller 6 and the conveyance roller 7.

Here, in this reference example , as shown in FIG. 5, the sensor arm 9 and the sensor 10, in other words, the detection unit that detects the sheet is located at the center of the sheet conveyance path 8 in the width direction orthogonal to the sheet conveyance direction. Is provided. In addition, the upper guide 5 and the lower guide 4 are symmetrically curved in the width direction from the center portion in the width direction. Since the lower and upper guides 4 and 5 have a curved shape in this way, the conveyed sheet is forced to have an arrow as shown in FIG. 6 regardless of the initial shape such as paper type, size, curl, etc. Are bent in a direction perpendicular to the sheet conveyance direction, that is, in the width direction of the sheet P.

  Then, by forcibly curving in this way, the sheet P is stiffened, and even when the sheet P initially has curl, the curl is corrected. As a result, the front end portion of the sheet P that has been crimped comes into contact with the sensor arm 9 at a fixed position according to the curved shape of the lower and upper guides 4 and 5. Thereby, the precision of the detection timing of the sensor 10 becomes high. Note that the curved portion Pr of the sheet P shown in FIG. 6 rotates and passes through the sensor arm 9 and returns to the original shape when passing through the conveying roller 6, so that a curved mark remains on the sheet P. Absent.

As described above, according to this reference example , the lower and upper guides 4 and 5 constituting the bending means have a curved shape, so that when the sheet P is detected by the sensor 10, the sheet P is bent in the width direction. Thus, the sheet P can be stiffened. As a result, the sheet P can be brought into contact with the sensor arm 9 at a fixed position regardless of the type of paper or the curl state, so that the contact position of the sheet tip to the sensor arm 9 can be stabilized. The detection accuracy of the sensor 10 can be increased.

  Further, since the lower and upper guides 4 and 5 constituting the sheet conveying path 8 are curved, there is no need to newly add rollers and rollers for curving the sheet, so there are disadvantages such as an increase in the number of parts and an increase in cost. The above effects can be obtained.

In the description so far, the case where the upstream side portion in the sheet conveying direction is curved with respect to the sensor arms 9 of the lower and upper guides 4 and 5 has been described, but the present reference example is not limited thereto. For example, the lower and upper guides 4 and 5 near the sheet sensor 15 in the sheet conveyance path 8 may be curved. Thereby, when the sheet is detected by the curved sheet sensor 15, the sheet is curved in the width direction, so that the sheet position detection accuracy of the sheet sensor 15 is stabilized, and variation in the image writing position with respect to the sheet P in the transfer unit is suppressed. Can do.

In the above, the detection means using the sensor arm 9 has been exemplified for detecting the position of the sheet. However, in this reference example in which the position in the thickness direction of the sheet is stable, an optical sensor is used as the detection means. Even in this case, the detection accuracy can be improved.

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

  FIG. 7 is a diagram showing a schematic configuration of a full-color laser beam printer which is an example of an image forming apparatus provided with a sheet conveying apparatus according to the present embodiment.

  In FIG. 7, reference numeral 100 denotes a full-color laser printer, and 100A denotes a full-color laser printer main body (hereinafter referred to as an apparatus main body). The apparatus main body 100A includes an image forming unit 52 that forms an image on a sheet, a sheet feeding device 53 that feeds the sheet, a fixing unit 17 that fixes a toner image formed on the sheet, and the like. .

  The image forming unit 52 includes a photosensitive drum 16a and the like, and is a process cartridge 16 (16Y, 16M, 16C, 16C) that forms toner images of four colors of yellow, magenta, cyan, and black, which are detachably attached to the apparatus main body 100A. 16K). The image forming unit 52 includes a scanner unit 11a that is arranged vertically below the process cartridge 16 and irradiates a laser beam based on image information to form an electrostatic latent image on the photosensitive drum 16a.

  Here, each process cartridge 16 includes, in addition to the photosensitive drum 16a, a charging roller 16b that uniformly charges the surface of the photosensitive drum, a developing roller 16c, a developer application roller 16d, a drum cleaning blade 16e, and the like. The fixing unit 17 applies heat and pressure to the image formed on the sheet to fix the toner image. The fixing unit 17 includes a heating roller 17b having a built-in heater and a pressure roller 17a in pressure contact with the heating roller 117b. Have.

  Reference numeral 23 denotes an intermediate transfer belt unit. The intermediate transfer belt unit 23 includes an intermediate transfer belt 23a that rotates counterclockwise. Here, the intermediate transfer belt 23a is stretched around the drive roller 23b and the tension roller 23c, and is tensioned in the arrow T direction by the tension roller 23c.

  A primary transfer roller 25 is provided inside the intermediate transfer belt 23a so as to face the photosensitive drum 16a, and is configured to apply a transfer bias by a bias applying unit (not shown). Then, as will be described later, by applying a primary transfer bias to the intermediate transfer belt 23a by the primary transfer roller 25, each color toner image on the photosensitive drum is sequentially transferred to the intermediate transfer belt 23a, thereby the intermediate transfer belt. A full color image is formed on the top.

  A secondary transfer unit 26 sequentially transfers a full color image formed on the intermediate transfer belt 23 a to a sheet, and includes a driving roller 23 b and a secondary transfer roller 60. Reference numeral 30 denotes a manual paper feed unit. The manual paper feed unit 30 includes an intermediate plate 31, a manual feed roller 32, and a separation pad 33 as a separation unit.

  Next, an image forming operation of the full color laser printer 100 configured as described above will be described.

  When an image forming signal is output from a control unit (not shown) provided in the apparatus main body 100A, laser light is emitted from the scanner unit 11a onto the photosensitive drum. At this time, the surface of the photosensitive drum 16a is uniformly charged to a predetermined polarity / potential in advance by the charging roller 16b, and an electrostatic latent image is formed on the surface by irradiating laser light from the scanner unit 11a. The Thereafter, the electrostatic latent image is developed with toner and visualized.

  For example, first, laser light of a yellow component color image signal is irradiated from the scanner unit 11a to the photosensitive drum 16a of the process cartridge 16Y to form a yellow electrostatic latent image on the photosensitive drum. The yellow electrostatic latent image is developed with yellow toner from the developing roller 16c and the developer application roller 16d, and visualized as a yellow toner image.

  Next, when the toner image arrives at the primary transfer portion where the photosensitive drum 16a and the intermediate transfer belt 23a come into contact with the rotation of the photosensitive drum 16a, the photosensitive drum is exposed to the primary transfer bias applied to the primary transfer roller 25. The yellow toner image on the body drum is transferred onto the intermediate transfer belt. Thereafter, when the portion carrying the yellow toner image of the intermediate transfer belt 23a moves, the magenta toner image formed on the photosensitive drum of the process cartridge 16M by the same method as described above is transferred from the yellow toner image. The image is transferred to the intermediate transfer belt 23a. Similarly, as the intermediate transfer belt 23a moves, the cyan toner image and the black toner image are transferred onto the yellow toner image and the magenta toner image, respectively, in the primary transfer portion.

  As a result, a full-color toner image is formed on the intermediate transfer belt. The toner remaining on the surface of the photosensitive drum after the toner image transfer is removed by the drum cleaning blade 16e. In parallel with the toner image forming operation, the sheet P accommodated in the sheet feeding cassette 12 is sent out by the feeding roller 13 provided in the sheet feeding device 53 and is provided in the sheet conveying path 8. Reach 20 Then, after the timing is adjusted by the registration roller pair 20, it is conveyed to the secondary transfer unit 26.

  The sheet P on the middle plate 31 of the manual feeding unit 30 is also pressed against the manual roller 32 as it rises on the middle plate 31, and then separated one by one by the rotation of the manual roller 32 and the separation pad 33. And transported. Then, the separated sheet P is conveyed to the refeed roller pair 35 through the manual sheet feed conveyance path 34, passes through the refeed conveyance path 36, and to the registration roller pair 20 provided in the sheet conveyance path 8. Be transported. Thereafter, the timing is adjusted by the registration roller pair 20 and then conveyed to the secondary transfer unit 26.

  Next, in the secondary transfer unit 26, the four color toner images on the intermediate transfer belt are collectively transferred onto the sheet by the secondary transfer bias applied to the secondary transfer roller 60. After the secondary transfer to the sheet P, the toner remaining on the intermediate transfer belt is removed by the transfer belt cleaning device 27, and the removed toner is collected as a waste toner (not shown) disposed on the back surface of the device. It is collected in a container.

  Next, the sheet P to which the toner image has been transferred is conveyed to the fixing unit 17, and the unfixed toner image on the sheet is heated and fixed when passing through the nip formed by the heating roller 17b and the pressure roller 17a. Is done. As a result, a full-color print image is fixed on the sheet as a permanent image. Next, after the full-color print image is fixed as a permanent image in this way, the sheet P is discharged and stacked on the sheet stacking unit 19 by the discharge roller pair 18.

  In FIG. 7, reference numeral 110 denotes a conveyance unit that is a sheet conveyance device that conveys the sheet P fed from the sheet feeding device 53 or the manual feeding unit 30 to the secondary transfer unit 26. The transport unit 110 includes a transport guide unit 310, a sheet pressure contact unit 210, and a sheet determination sensor unit 400 shown in FIGS.

  Here, the sheet determination sensor unit 400 detects the transmitted light LED 400a for determining the thickness of the sheet, the reflected light LED 400b for determining the type of the sheet, and the sizes of the transmitted light and the reflected light. The optical sensor 400c is used. Further, the conveyance guide unit 310 includes a conveyance guide 312 that is provided in parallel with the guide surface 311 and the width direction and has a plurality of ribs 312a to 312h extending in the sheet conveyance direction, and includes a reflected light LED 400b and an optical sensor 400c. keeping.

  The sheet discrimination sensor unit 400 constituting the detection means discriminates characteristics such as sheet thickness and type, and a control unit (not shown) determines the sheet characteristics discriminated by the sheet discrimination sensor unit 400. Accordingly, control is performed to change the image forming conditions. In addition, the following are mentioned as control by a control part.

  For example, if the sheet type (surface) is gloss paper, which has a higher gloss than plain paper, the development bias is increased compared to plain paper, and the amount of toner adhering to the surface of the sheet is increased to increase the gloss of the image on the sheet. Control to increase the degree.

  Further, the fixing temperature is controlled to be changed according to the thickness of the sheet. For example, in the case where the sheet is thick paper that is thicker than plain paper, the thick paper has a larger heat capacity than the plain paper, so that fixing performance is deteriorated even if the toner image is fixed on the thick paper at the same fixing temperature as the plain paper. Therefore, when it is determined that the sheet is thick paper, the fixing temperature is set to a temperature higher than the fixing temperature of plain paper, and control is performed so as to ensure toner fixability on the thick paper.

  Further, the type of the sheet is determined, and control is performed so as to change the sheet conveyance speed in accordance with the result. For example, if the type of sheet is thick paper that is thicker than plain paper, the thick paper has a larger heat capacity than plain paper, so the fixability will deteriorate even if the toner image is fixed on the thick paper at the same transport speed as plain paper. End up. Therefore, if it is determined that the sheet type is cardboard, the sheet transport speed is slower than the transport speed when passing plain paper so that the amount of heat supplied to the cardboard per unit time is increased. Set.

  Also, control is performed so that the fixing temperature condition is changed for sheets having different basis weights. For example, a sheet having a relatively large thickness has a large heat capacity, so that the fixing temperature is controlled to be high, and a sheet having a relatively small thickness, that is, a sheet having a small heat capacity, is fixed at a low fixing temperature. Further, the sheet conveyance speed can be changed and controlled according to the basis weight of the sheet.

  In the case of OHT or glossy paper, it is possible to improve the image quality by discriminating these and improving the fixability of the toner adhering to the surface of the sheet and increasing the gloss. As described above, in this embodiment, control is performed so as to change the developing bias condition, the fixing temperature, or the sheet conveyance speed based on the result of determination (detection) of the sheet characteristics.

  On the other hand, as shown in FIG. 9, the sheet pressing unit 210 holds the transmitted light LED 400a, and includes a swing guide 214 and a pair of rotatable pressing rollers 211 arranged on both sides of the transmitted light LED 400a. Composed.

  The sheet pressing unit 210 is biased counterclockwise by the pressing spring 212 around the rotation center 213. Further, the pressing roller 211 as a pressing member has a rotation center in the same phase as the transmitted light LED 400a in the sheet conveyance direction, and a part of the conveyance guide 312 disposed opposite to the sheet conveyance path 8 in the width direction. Is in pressure contact with the guide surface 311.

  Further, the swing guide 214 of the sheet pressing unit 210 and the conveyance guide 312 of the conveyance guide unit 310 constitute a part of the sheet conveyance path 8. In other words, in the present embodiment, a part of the sheet conveyance path 8 is formed by the swing guide 214 of the sheet pressing unit 210 as one guide member and the conveyance guide 312 of the conveyance guide unit 310 as the other guide member. Composed.

  By the way, when discriminating the thickness and type of the sheet, in the detection unit 400A that discriminates (detects) the thickness and type of the sheet by the transmitted light LED 400a and the reflected light LED 400b, the variation in the posture of the sheet is suppressed, and the sheet is Must be located within the focal range.

  Therefore, in the present embodiment, as shown in FIGS. 10A and 10B, the sheet thickness direction heights of the ribs 312a to 312h of the conveyance guide 312 of the conveyance guide unit 310 are detected in the width direction. The distance increases from the portion 400A. In the present embodiment, the height of the rib 312h farthest from the detection portion 400A is higher by Hmm in the sheet thickness direction than the nip portion N formed by the guide surface 311 and the pressure roller 211.

  By setting the height of the rib 312h in this way, when passing through the nip portion N formed by the guide surface 311 and the pressure contact roller 211, the posture of the sheet P is the downstream side in the sheet conveying direction as shown in FIG. As seen from the arrow W1. As a result, the variation in the distance between each LED and the sheet P in the detection unit 400A of the sheet determination sensor unit 400 can be reduced.

  Next, a sheet determination operation by the sheet determination sensor unit 400 when passing through the transport unit 110 configured as described above will be described.

  The sheet P fed from the sheet feeding device 53 or the manual feeding unit 30 is first transported to the rotating registration roller pair 20 by a driving source (not shown). Next, the sheet P is conveyed to a predetermined distance by the registration roller pair 20 after passing through a nip portion N formed by a guide surface 311 and a pressure roller 211 arranged downstream of the registration roller pair 20 in the sheet conveyance direction. The

  Thereafter, the detection unit 400A of the sheet determination sensor unit 400 temporarily stops, and a determination operation for determining characteristics such as the thickness and type of the sheet P is performed in a state where the sheet P is stopped in this manner. At this time, the height of the ribs 312a to 312h of the conveyance guide 312 increases in the sheet thickness direction as the distance from the detection unit 400A increases.

  That is, the height in the sheet thickness direction of the plurality of ribs 312a to 312h constituting the bending means is higher toward the outer rib in the width direction. Accordingly, the height in the sheet thickness direction of the rib located on the outer side in the width direction is higher than the nip portion N between the pressing roller 211 and the guide surface 311 that is a contact portion between the pressing roller 211. As a result, as shown in FIG. 11, the posture of the sheet P becomes convex as indicated by an arrow W1 when viewed from the downstream side in the sheet conveying direction.

  Here, in the case of the full color laser printer 100, the sheet P fed from the sheet feeding device 53 is easily bent in the direction opposite to the arrow W1 shown in FIG. 11 and fed from the manual sheet feeding unit 30. The sheet P is easily bent in the direction of the arrow W1. That is, since the posture of the sheet P is different between the case where the sheet P is fed from the sheet feeding device 53 and the case where the sheet P is fed from the manual feeding unit 30, the posture of the sheet P when it is conveyed to the detection unit 400A. Variations occur.

  However, by setting the height of the ribs 312a to 312h as in the present embodiment, even when the sheet is curved and the sheet is fed from either the sheet feeding device 53 or the manual feeding unit 30, In the detection unit 400A, the posture of the sheet is convex. As a result, the variation in the distance between each LED and the sheet in the detection unit 400A can be reduced, and the detection accuracy of the sheet determination sensor unit 400 can be increased. After the detection operation is completed, the sheet P is conveyed again to the secondary transfer unit 26 by the registration roller pair 20.

  As described above, the sheet P is detected by increasing the height in the sheet thickness direction of the ribs 312a to 312h as the distance from the detection unit 400A increases in the width direction as in the present embodiment. In this case, the sheet P can be curved in the width direction. Thereby, the sheet thickness and type detection accuracy of the sheet discrimination sensor unit 400 can be increased regardless of the sheet type and curl state of the sheet.

  In the present embodiment, by increasing the height in the sheet thickness direction of the rib located on the outer side in the width direction than the nip portion N between the pressure roller 211 and the guide surface 311, the sheet posture is set in the sheet conveyance direction. The convex shape is seen from the downstream side. In other words, by increasing the height in the sheet thickness direction of the rib located on the outer side in the width direction, the height of the rib in the thickness direction in the center in the width direction is increased, so that the posture of the sheet is viewed from the downstream side in the sheet conveyance direction. To be convex.

  However, the present embodiment is not limited to this, and the height of the rib in the sheet thickness direction of the rib located on the outer side in the width direction than the nip portion N between the press-contact roller 211 and the guide surface 311 is reduced, so The same effect can be obtained even if the configuration is concave. That is, if the nip portion N between the pressure roller 211 and the guide surface 311 is different from the height in the sheet thickness direction of the rib located on the outer side in the width direction, the above-described effect can be obtained.

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

  FIG. 12 is a diagram illustrating a configuration of a transport unit that is a sheet transport apparatus according to the present embodiment. In FIG. 12, the same reference numerals as those in FIG. 10 described above indicate the same or corresponding parts.

  In FIG. 12, reference numeral 120 denotes a conveyance unit, and the conveyance unit 120 includes a conveyance guide unit 320, a sheet pressure contact unit 220, and a sheet determination sensor unit 400.

  Here, the conveyance guide unit 320 includes a conveyance guide 322 having a guide surface 321 and holds a reflected light LED 400b and an optical sensor 400c. The guide surface 321 of the conveyance guide unit 320 has a square shape so as to be substantially line symmetric with respect to the center of the detection unit 400A of the sheet determination sensor unit 400 in the width direction when viewed from the downstream side in the sheet conveyance direction. It is provided in the shape.

  That is, the guide surface 321 of the conveyance guide unit 320 constituting the bending unit is inclined in the thickness direction of the sheet as the distance from the central portion in the width direction of the detection unit 400A increases in the width direction. In the present embodiment, the guide surface 321 of the transport guide unit 320 is arranged such that the optical sensor 400c is moved away from the center in the width direction of the detection unit 400A as shown in FIGS. 12 (a) and 12 (b). It is inclined α ° on the opposite side.

  The sheet press-contact unit 220 holds the transmitted light LED 400a, and includes a swing guide 224 and a pair of rotatable press-contact rollers 221. The press-contact spring 222 rotates counterclockwise around the rotation center 223. Be energized. By being urged in this way, the pressure contact roller 221 of the sheet pressure contact unit 220 is in pressure contact with the guide surface 321 that is a part of the conveyance guide 322.

  Here, similarly to the guide surface 321, the press-contact roller 221 is also substantially symmetrical with respect to the center of the detection unit 400A of the sheet determination sensor unit 400 in the width direction when viewed from the downstream side in the sheet conveyance direction. It is provided in a letter shape. That is, the press contact roller 221 is inclined in the thickness direction of the sheet as it is farther from the center in the width direction of the detection unit 400A. In the present embodiment, this press-contact roller 221 is also inclined by α ° on the side opposite to the optical sensor 400c side as it moves away from the center in the width direction of the detection unit 400A.

  By configuring the guide surface 321 and the pressure contact roller 221 in this way, the sheet P is curved when passing through the nip portion formed by the guide surface 321 and the pressure contact roller 221, and the posture of the sheet P as shown in FIG. Becomes convex as indicated by an arrow W2 when viewed from the downstream side in the sheet conveying direction. As a result, variation in the distance between each LED and the sheet in the detection unit 400A can be reduced, and the detection performance of the sheet determination sensor unit 400 can be improved. Further, by configuring as in the present embodiment, it is possible to reduce the occurrence of rib marks due to the ribs 312a to 312h of the conveyance guide 312 on the image on the sheet.

  In the present embodiment, the detection unit of the sheet determination sensor unit 400 is configured such that the sheet posture is convex when viewed from the downstream side in the sheet conveyance direction, but the sheet posture is concave. The same effect can be obtained with the configuration.

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

  FIG. 14 is a diagram illustrating a configuration of a transport unit that is a sheet transport apparatus according to the present embodiment. In FIG. 14, the same reference numerals as those in FIG. 10 described above indicate the same or corresponding parts.

  In FIG. 14, reference numeral 140 denotes a conveyance unit, and the conveyance unit 140 includes a conveyance guide unit 340, a sheet pressure contact unit 240, and a sheet determination sensor unit 400.

  Here, the conveyance guide unit 340 includes a reflected light LED 400b and an optical sensor 400c, a conveyance guide 342 having a guide surface 341, and a sensor protection guide 343 that covers the reflected light LED 400b and the optical sensor 400c. ing. The guide surface 341 is provided in a square shape so as to be substantially line symmetric with respect to the center of the sheet determination sensor unit 400 in the width direction when viewed from the downstream side in the sheet conveyance direction.

  That is, the guide surface 341 of the conveyance guide unit 340 is inclined in the thickness direction of the sheet as it is farther from the center in the width direction of the detection unit 400A. In the present embodiment, the guide surface 341 of the transport guide unit 340 is inclined γ ° toward the side opposite to the optical sensor 400c as it goes outward as shown in FIG. 14B.

  The sheet pressing unit 240 holds the transmitted light LED 400a, and includes a swing guide 244 and a pair of rotatable pressing rollers 241. The pressing spring 242 rotates counterclockwise around the rotation center 243. Be energized. By being biased in this way, the pressure contact roller 241 of the sheet pressure contact unit 240 comes into pressure contact with the guide surface 341 that is a part of the conveyance guide 342.

  Here, the pressing roller 241 is also provided in a square shape so as to be substantially line symmetric with respect to the center of the detection unit 400A of the sheet determination sensor unit 400 in the width direction when viewed from the downstream side in the sheet conveyance direction. ing. That is, the pressing roller 241 is inclined in the thickness direction of the sheet as it moves away from the central portion in the width direction of the detection unit 400A. In the present embodiment, the pressure contact roller 221 is also inclined γ ° toward the side opposite to the optical sensor 400c side as the distance from the central portion in the width direction of the detection unit 400A increases.

  By configuring the guide surface 341 and the pressure contact roller 241 in this way, the sheet is curved when passing through the nip portion formed by the guide surface 341 and the pressure contact roller 241, and the sheet P is formed as shown in FIG. The posture is convex when viewed from the downstream side in the sheet conveying direction. And since it becomes convex in this way, the sheet | seat P comes to contact | abut to the sensor protection guide 343 which is a cover member, As a result, the distance of each LED and a sheet | seat becomes always constant, and also sheet | seat discrimination | determination sensor unit 400 detection performance is improved.

  Note that, when the sheet P is brought into contact with the sensor protection guide 343 as in the present embodiment, there is a concern about the surface of the sensor protection guide being scraped by friction with the sheet P. For example, it is preferable to use a material that is difficult to cut, such as glass.

In the above description, the case where the guide surface 341 and the pressure contact roller 241 are inclined has been described. However, the present embodiment is not limited to this, and the configuration of the ribs 312a to 312h shown in the above-described reference example is used so that the posture of the sheet P is convex when viewed from the downstream side in the sheet conveyance direction. The sheet P may be brought into contact with the protective guide 343.

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

  FIG. 16 is a diagram illustrating a configuration of a transport unit that is a sheet transport apparatus according to the present embodiment. In FIG. 16, the same reference numerals as those in FIG. 10 described above indicate the same or corresponding parts.

  In FIG. 16, reference numeral 130 denotes a conveyance unit. The conveyance unit 130 includes a conveyance guide unit 330, a sheet pressure contact unit 230, and a sheet determination sensor unit 400.

  Here, the conveyance guide unit 330 includes a conveyance guide 332 having a guide surface 331, and holds the reflected light LED 400b and the optical sensor 400c. The sheet press-contact unit 230 holds the transmitted light LED 400a, and includes a swing guide 234 and a pair of rotatable press-contact rollers 231. The press-contact spring 232 rotates counterclockwise about the rotation center 233. It is energized. By being biased in this way, the pressure contact roller 231 of the sheet pressure contact unit 230 comes into pressure contact with the guide surface 331 which is a part of the conveyance guide 332.

  By the way, in the present embodiment, as shown in FIGS. 17A and 17B, the pressure roller 231 has an upstream angle β of 90 of the angle formed by the rotation axis of the pressure roller 231 and the sheet conveying direction. It is less than °. That is, the press roller 231 is inclined toward the upstream side in the sheet conveying direction as the distance from the central portion in the width direction of the detection unit 400A increases.

  Here, by inclining the pressure contact roller 231 toward the upstream side in the sheet conveying direction, when passing through the nip formed by the guide surface 341 and the pressure contact roller 241, the wrinkles and the deflection of the sheet are stretched outward in the width direction. It is. In this way, the application means for applying a force that stretches the sheet to the both sides of the sheet constituted by the pressure roller 231 and the guide surface 341 extends the wrinkles and the deflection of the sheet outward in the width direction.

  And, as the wrinkles and deflection of the sheet are stretched outward in the width direction in this way, the variation in the distance between each LED and the sheet in the detection unit 400A can be reduced, and the detection performance of the sheet determination sensor unit 400 can be further improved. Can do. In addition, by extending the sheet wrinkles and bends outward in the width direction as described above, even when the sheet P is bent, the occurrence of paper wrinkles in the roller nip downstream of the transport unit 130 can be reduced.

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

  FIG. 18 is a diagram illustrating a configuration of a transport unit that is a sheet transport apparatus according to the present embodiment. In FIG. 18, the same reference numerals as those in FIG. 10 described above indicate the same or corresponding parts.

  In FIG. 18, reference numeral 150 denotes a conveyance unit. The conveyance unit 150 includes a conveyance guide unit 350, a sheet pressure contact unit 250, and a sheet determination sensor unit 400.

  The transport guide unit 350 includes a reflected light LED 400b, a light sensor 400c, a transport guide 352 having a guide surface 351, and registration rollers 20a and 20b. The registration rollers 20a and 20b are arranged to face each other across the conveyance path 8 by a pressing spring (not shown) and are pressed against the registration rollers 20c constituting the registration roller pair 20 together with the registration rollers 20a and 20b.

  The sheet pressing unit 250 holds the transmitted light LED 400a, and includes a swing guide 254, a pair of rotatable pressing rollers 251 and a registration roller 20c. A center of rotation 253 is centered by a pressing spring 252. It is urged counterclockwise. By being urged in this way, the pressure contact roller 251 of the sheet pressure contact unit 250 is in pressure contact with the guide surface 351 that is a part of the conveyance guide 352.

  Incidentally, in the present embodiment, as shown in FIGS. 19 and 20, the registration roller 20a close to the detection unit 400A has an upstream angle δ of 90 of the angle formed by the rotation axis of the registration roller 20a and the sheet conveyance direction. It is less than °. That is, as the registration roller 20a is farther from the center in the width direction of the detection unit 400A, in other words, the outer end in the width direction is inclined upstream in the sheet conveying direction.

  When the sheet is conveyed to the registration roller pair 20 by inclining the registration roller 20a close to the detection unit 400A in this way, the wrinkles and deflection of the sheet P are moved outward in the width direction due to the inclination of the registration roller 20a. Stretched. In other words, in the present embodiment, wrinkles and deflections of the sheet are extended outward in the width direction by an applying unit that is configured by the inclined registration rollers 20a and applies a force that stretches the sheet to both sides.

  Then, the sheet P on which the wrinkles and the bends are extended is formed between the guide surface 351 and the pressure roller 251 shown in FIG. 19 by the registration roller pair 20 which is a pair of conveyance rollers provided on the upstream side of the pressure roller 251 in the sheet conveyance direction. It is conveyed from the nip portion N to a predetermined distance downstream. Thereafter, the sheet determination sensor unit 400 temporarily stops at the detection position.

  Next, a detection operation for determining the thickness and type of the sheet P is performed. At this time, since the sheet P is wrinkled and bent by the registration roller pair 20, the variation in the distance between each LED and the sheet in the detection unit of the sheet determination sensor unit 400 can be reduced. Detection performance can be improved.

  In this embodiment, the upstream angle δ of the rotation axis of the registration roller 20a and the sheet conveyance direction is less than 90 °. However, the present embodiment is not limited to this. For example, even when the angle δ is 90 °, as shown in FIG. 21, the diameter (diameter) of the resist roller 20a or 20b becomes farther from the center in the width direction of the detection unit in the width direction, in other words, the outer end in the width direction. The same effect can be obtained by reducing.

In the embodiment of the first to 5, as detection means, for detecting the type of sheet, and a LED400a transmitted light, and LED400b reflection light, the optical sensor comprising a light sensor 400c Illustrated. However, the above-described embodiment in which the position of the sheet in the thickness direction is stable can also be applied to a detection unit that detects the position of the sheet using a sensor arm, and in this case also, the detection accuracy can be improved.

4 Lower guide 5 Upper guide 8 Sheet conveyance path 9 Sensor arm 10 Sensor 20 Registration roller pair 20a, 20b Registration roller 20c Registration roller 50 Laser printer 51 Laser printer main body 52 Image forming unit 54 Sheet conveyance device 100 Full color laser printer 100A Full color laser printer Main body 110, 120, 130, 140, 150 Conveyance unit 210, 220, 230, 240, 250 Sheet pressure unit 211, 221, 231, 241, 251 Pressure roller 214, 224, 234, 244, 254 Swing guide 310, 320 , 330, 340, 350
311, 321, 331, 341, 351 Guide surfaces 312, 322, 332, 342, 352 Transport guides 312 a to 312 h Rib 343 Sensor protection guide 400 Sheet discrimination sensor unit 400 A Detection unit 400 a LED for transmitted light
400b LED for reflected light
400c Optical sensor P sheet

Claims (8)

Conveying means for conveying the sheet;
A first guide for guiding one surface of the sheet conveyed by said conveying means,
A second guide for guiding the other surface of the sheet conveyed by the conveying means;
An LED provided on one of the first guide and the second guide, and a photosensor provided on the other of the first guide and the second guide, and a sheet at a detection position Detecting means for detecting at least one of the thickness and the surface property ;
Two rotating bodies provided on the first guide and provided on the outer side and both sides of the detection position in the width direction orthogonal to the sheet conveying direction;
Wherein as the two rotating bodies form the second guide and the nip portion, and a biasing means for biasing said first guide to the second guide,
The second guide has a plurality of conveying ribs on the outer side of each nip portion with the two rotating bodies in the width direction, and the height of the plurality of conveying ribs in the thickness direction is: The height of the sheet is higher than the nip portion, and the height increases toward the outside in the width direction. When viewed from the downstream side in the sheet conveyance direction, the sheet posture is convex with the detection position as the top. sheet conveying apparatus according to claim Rukoto is curved sheet to be shaped. The guide surface of the second guide, the detection position as the top of claim 1 Symbol placement of the sheet conveying device and being inclined in the thickness direction and the width direction of the sheet. The rotator, the detection position as the top, the sheet conveying apparatus according to claim 1, wherein that it is inclined in the thickness direction and the width direction of the sheet. The angle formed by a direction in which the conveying unit conveys the sheet and a rotation shaft that holds the rotating body is less than 90 °, according to any one of claims 1 to 3 . Sheet conveying device. The rotating body, the outer diameter of the width direction, the sheet conveying device according to any one of claims 1 to 4, characterized in that less than the inner diameter of the width direction. Sheet conveying device according to any one of claims 1 to 5 having a protection guide that covers the optical sensors. Before SL based on the detection result detecting means, the sheet conveying device according to any one of claims 1 to 6, characterized in that it has a control means for changing an image forming condition. An image forming unit, an image forming apparatus characterized by comprising a sheet conveying device according to any one of claims 1 to 7.

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