JP4657091B2 - Image forming apparatus - Google Patents

Description

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

  An image forming apparatus configured as a copying machine, a printer, a facsimile machine, a printing machine, or a multifunction machine having at least two of these functions has been conventionally known (see, for example, Patent Document 1). When an image is formed on a sheet by such an image forming apparatus, if the positional accuracy of the image with respect to the sheet is low, a part of the image may be lost or a large margin may be formed. For example, in bookbinding printing or saddle stitch printing, when the image-formed paper is cut together, if the position of the image with respect to the paper is greatly displaced, depending on the image, a large margin may remain on the paper, Will be lost, resulting in a definite defect in the finished product.

  Therefore, the sheet position in the direction orthogonal to the sheet conveyance direction is detected by the sheet position detection unit, and the position of the image with respect to the sheet is corrected based on the detection result, thereby improving the position accuracy of the image with respect to the sheet. An image forming apparatus capable of performing the above has been proposed. However, in this type of conventional image forming apparatus, it is difficult to increase the detection accuracy when detecting the paper position. Even if the position of the image relative to the paper is corrected based on the detection result, the image on the paper The position accuracy could not be improved as expected.

JP-A-8-267852

  An object of the present invention is to provide an image forming apparatus capable of improving the detection accuracy of the paper position as compared with the conventional art.

  In order to achieve the above object, the present invention provides an image forming unit that forms an image on a sheet to be conveyed, and a sheet position detecting unit that detects a sheet position in a direction orthogonal to the sheet conveying direction toward the image forming unit. And the paper position detecting means is an image forming apparatus disposed upstream of the image forming position where the image forming means forms an image on the paper in the paper transport direction. The paper transport speed is determined when the paper position is detected by the paper position detecting means, and when the paper is positioned upstream or downstream in the paper transport direction from the paper position detecting means. An image forming apparatus is proposed that is configured to be switchable to a non-detection speed, and that the detection-time speed is lower than the non-detection speed (claim 1).

  In the image forming apparatus according to claim 1, when the paper position is detected by the paper position detection unit, the transport speeds of all the sheets positioned upstream of the paper in the paper transport direction are also detected. It is advantageous to configure to switch to speed (Claim 2).

  Furthermore, in the image forming apparatus according to claim 1 or 2, the paper transport speed when detecting the paper position is switched to the detection speed only when the image position high accuracy mode is selected. This is advantageous (claim 3).

  4. The image forming apparatus according to claim 1, wherein the sheet position detection unit includes a light emitting unit and a light receiving unit, and the light emitting unit includes at least one light emitting element. The section is composed of a light receiving element array in which a plurality of light receiving elements are arranged in a line at almost equal intervals, and is configured to determine the width direction end of the paper depending on whether the light reception output of each light receiving element is equal to or greater than a threshold value. (Claim 4).

  Furthermore, the image forming apparatus according to any one of claims 1 to 4 can be configured as a copier, a printer, a facsimile, or a multifunction machine having at least two of these functions (claim 5).

  According to the present invention, it is possible to improve the detection accuracy of the paper position.

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

  FIG. 1 is a schematic diagram illustrating an example of an image forming apparatus. This image forming apparatus has an image forming means 1 for forming an image on a sheet to be conveyed. The image forming means 1 shown here includes an image carrier 2 configured as a drum-shaped photoconductor, and a charging device. 3, an exposure device 4, a developing device 8, a transfer device 5, a cleaning device 6, and a fixing device 7. During the image forming operation, the image carrier 2 is driven to rotate in the clockwise direction in FIG. 1. At this time, the image carrier is charged to a predetermined polarity by the charging device 3, and the light modulation emitted from the exposure device 4 on the charging surface. The irradiated laser beam L is irradiated, whereby an electrostatic latent image is formed on the image carrier 2. This electrostatic latent image is visualized as a toner image by the developing device 8.

  On the other hand, the paper P sent out from a paper feeder (not shown) is transported in the direction of arrow A by the transport roller pairs 9 and 10, and the image carrier 2 and the transfer device at a predetermined timing by the rotation of the registration roller pair 11. Sent between 5. The transfer device 5 shown here has a transfer belt 12 wound around a plurality of rollers and driven to rotate in the direction of the arrow, and a transfer roller 13. The paper P is fed between the transfer belt 12 and the image carrier 2 and is carried on the transfer belt 12 and conveyed. At this time, the toner image on the image carrier 2 is transferred to the paper P by the action of the transfer voltage applied to the transfer roller 13. When the paper P passes through the fixing device 7, the toner image transferred to the paper P is fixed. The paper that has passed through the fixing device 7 is discharged to a paper discharge tray (not shown). On the other hand, the transfer residual toner adhering to the image carrier 2 after the toner image transfer is removed by the cleaning device 6. The image forming apparatus shown in FIG. 1 is configured as, for example, an electronic copying machine, a laser beam printer, a facsimile, or a multifunction machine having at least two of these functions.

  As described above, an image is formed on the paper P. In order to improve the positional accuracy of the image with respect to the paper P, the image forming apparatus according to the present embodiment has a paper transport direction A toward the image forming unit 1. The sheet position detecting means 14 for detecting the sheet position in the orthogonal direction is provided. The sheet position detecting unit 14 is disposed upstream of the image forming position where the image forming unit 1 forms an image on the sheet P in the sheet conveying direction. In the illustrated example, the paper position detection means 14 is provided upstream of the transfer position where the toner image on the image carrier 2 is transferred to the paper P in the paper transport direction.

  FIG. 2 is an explanatory diagram schematically showing an example of the transmissive paper position detecting means 14. The paper position detection means 14 shown here includes a light emitting unit 15 having a light emitting element 17 and a light receiving unit 16. Although the light emitting unit 15 shown here is constituted by one light emitting element 17, the light emitting part can also be constituted by a plurality of light emitting elements. The light emitting part is composed of at least one light emitting element. The light receiving unit 16 is composed of a light receiving element array in which a plurality of light receiving elements 18 are arranged in a line at substantially equal intervals. The paper P shown in FIG. 2 is transported in a direction perpendicular to the paper surface of FIG. 2, and the plurality of light receiving elements 18 are arranged in a direction orthogonal to the paper transport direction A (FIG. 1). .

  In order to detect the width direction end E of the paper P by the paper position detecting means 14, when the paper P reaches the paper position detecting means 14, the light emitting element 17 of the light emitting portion 15 emits light, and the light is guided to the light guide 19. To the light receiving element 18. In FIG. 2, the light traveling toward the light receiving element 18 is indicated by an arrow. As can be seen from this figure, the amount of light incident on the light receiving element 18 </ b> A facing the paper P is small and does not face the paper P. A large amount of light is incident on the light receiving element 18B. Therefore, the end E of the paper P can be determined by the light reception output of each light receiving element 18. More specifically, a control unit (not shown) determines whether or not the light reception output of each light receiving element 18 is equal to or greater than a threshold value, and thereby determines the width direction end E of the paper P. As the paper P, in addition to general plain paper, thick paper, thin paper, second base paper, and the like are used. Any paper can detect the end E in the width direction by the paper position detecting means 14. .

  As described above, the shift of the sheet position in the direction orthogonal to the sheet conveyance direction is detected, and the exposure apparatus 4 shown in FIG. 1 performs main scanning with respect to the image carrier 2 based on the detection result. The position where the laser beam starts to be irradiated in the direction is corrected, the electrostatic latent image formed thereby is visualized as a toner image by the developing device 8, and the toner image is transferred to the paper P. As described above, by correcting the position of the image with respect to the paper P based on the detection result by the paper position detection unit 14, the positional accuracy of the image with respect to the paper P can be improved.

  3 and 4 show the reflection type paper position detecting means 14. The paper position detecting means 14 includes a light emitting unit 15 composed of a plurality of light emitting elements 17 arranged in a direction orthogonal to the conveyance direction A of the paper P, and a direction orthogonal to the conveyance direction A of the paper P. The light receiving section 16 is composed of a plurality of light receiving elements 18 arranged in a line at almost equal intervals. When the paper P passes through the paper position detecting means 14, each light emitting element 17 emits light, and the width direction end E of the paper P is determined depending on whether or not the light receiving output of each light receiving element 18 is equal to or greater than a threshold value. The

  When detecting the width direction end E of the paper P by the paper position detecting means 14 configured as described above, in order to increase the detection accuracy, the behavior of the paper P at the time of detection is stabilized, and the light receiving unit 16 need to be input. Thus, in order to stabilize the behavior of the paper P, it is preferable to detect the width direction end E of the paper P by slowing the conveyance speed of the paper P, ideally stopping the paper P. However, once the paper P is stopped, the image forming speed is lowered, and the influence is particularly great in a high-speed machine.

  Therefore, in the image forming apparatus of this example, the conveyance speed of the sheet P in the sheet conveyance direction is determined by the detection speed when the sheet position is detected by the sheet position detection unit 14 and the sheet P is detected by the sheet position detection unit 14. It is configured to be switchable to the non-detection speed when positioned upstream or downstream in the paper transport direction, and the detection speed is configured to be lower than the non-detection speed. Yes. More specifically, the paper P is sent out from a paper feeding device (not shown) at a non-detection speed V1, and is detected at a non-detection speed V1 by the paper conveyance means including the conveyance roller pairs 9 and 10 shown in FIG. And is sent toward the paper position detecting means 14. Thus, the non-detection speed V1 is a normal conveyance speed of the paper. At the same time when the paper P reaches the paper position detecting means 14, the rotational speed of the pair of transport rollers 9 and 10 is reduced, and the transport speed of the paper P is changed to a detection speed V2 which is lower than the non-detection speed V1. . The end E in the width direction of the paper P conveyed at this low detection speed V2 is detected by the paper position detecting means 14 as described above. Simultaneously with the end of detection of the width direction end E of the paper P, the transport speed of the paper P is returned to the non-detection speed V1, which is a normal speed. As described above, when the paper position in the direction orthogonal to the paper transport direction A is detected by the paper position detection means 14, the transport speed of the paper P is detected speed V2 which is lower than the normal non-detection speed V1. Therefore, the detection accuracy can be increased, and the accuracy of the image position with respect to the paper P can be further improved. In addition, since the paper P is not stopped at the time of this detection, the image forming speed is not greatly reduced, and particularly the print productivity when continuously feeding the paper and performing the continuous printing operation is greatly reduced. Can be prevented.

  5 and 6 are graphs in which the horizontal axis represents the arrangement direction of the light receiving elements of the paper position detecting means 14 and the vertical axis represents the light receiving output of each light receiving element. FIG. 5 shows the light reception output of the transmission type paper position detection means 14 shown in FIG. 2, and FIG. 6 shows the light reception output of the reflection type paper position detection means 14 shown in FIGS. A solid line X in these drawings indicates a light reception output when the width direction end E of the sheet is detected while the sheet is conveyed at the non-detection speed V1, which is a normal conveyance speed of the sheet. Indicates a light reception output when the width direction edge E of the paper is detected while the paper is conveyed at the detection speed V2. Depending on whether or not the light receiving output of the light receiving element 18 is equal to or greater than the threshold value, the actual width direction edge E of the sheet is detected. At this time, as can be seen from FIGS. When the portion E is detected, the end portion E of the paper P can be accurately detected when the paper P is conveyed at the low detection speed V2.

  Although the detection speed V2 depends on the performance of the paper position detection means 14, it may be a speed that can accurately detect the edge E of the paper in the width direction. If the part E can be detected, the detection speed V2 can be made equal to the non-detection speed V1.

  Further, when the paper position is detected by the paper position detecting means 14, the transport speed of all the papers positioned upstream of the paper P in the paper transport direction is also the same as the switching of the transport speed of the paper P. At this time, the detection speed V2 is switched, and at the same time as the detection of the paper position is completed, the conveyance speed of all sheets positioned upstream of the position-detected paper P in the paper conveyance direction is returned to the non-detection speed V1. It is preferable. By adopting such a configuration, even if there is a difference between the detection speed and the non-detection speed, the speed of the paper P whose position is detected and the speed of the paper positioned upstream from this are equal. , Jam can be prevented.

  As described above, according to the image forming apparatus of this example, it is possible to effectively suppress a decrease in the image forming speed. However, depending on the performance of the paper position detecting unit 14, the paper detection speed V2 is not detected. It is also conceivable that the speed must be set much lower than the hourly speed V1. In such a case, there is a possibility that the image forming speed is considerably reduced. Therefore, it is preferable that the conveyance speed of the paper P when the paper position is detected is switched to the detection speed V2 only when the image position high accuracy mode is selected. For example, as shown in FIG. 7, an ON key 21 and an OFF key 22 for selecting the image position high accuracy mode are provided in the operation unit 20 of the image forming apparatus, and when the user presses the ON key 21, the sheet position is changed. At the time of detection, the speed of the paper is set to the detection speed V2. Thereby, the width direction edge E of the paper P can be detected with high accuracy, and the accuracy of the image position with respect to the paper P can be increased. On the other hand, when the user presses the OFF key 22, the sheet position is not detected by the sheet position detecting means 14, and the sheet is conveyed from the beginning to the end at a high non-detection speed, thereby increasing the image forming speed. Increase. When the user presses the OFF key 22, the edge E of the paper can be detected while the paper is conveyed at a high non-detection speed. In this way, the image forming operation can be performed in the mode desired by the user.

1 is a schematic diagram illustrating an example of an image forming apparatus. It is explanatory drawing which shows typically a transmissive | pervious sheet | seat position detection means. It is an explanatory view of a reflection type paper position detection means. It is an explanatory view of a reflection type paper position detection means. It is a graph which shows the light reception output of a light receiving element. It is a graph which shows the light reception output of a light receiving element. It is a front view which shows an operation part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming means 14 Paper position detection means 15 Light emitting part 16 Light receiving part 17 Light emitting element 18, 18A, 18B Light receiving element A Paper conveyance direction P Paper

Claims (5)

Image forming means for forming an image on the conveyed paper; and paper position detecting means for detecting a paper position in a direction orthogonal to the paper conveying direction toward the image forming means. In the image forming apparatus disposed upstream of the image forming position where the image forming unit forms an image on the sheet, the sheet position detecting unit determines the sheet conveying speed in the sheet conveying direction. It is possible to switch between a detection speed when the paper position is detected and a non-detection speed when the paper is positioned upstream or downstream in the paper transport direction with respect to the paper position detection means. The image forming apparatus is characterized in that the detection speed is lower than the non-detection speed. 2. The image forming apparatus according to claim 1, wherein when the paper position is detected by the paper position detecting unit, the transport speed of all the sheets positioned upstream of the paper in the paper transport direction is also switched to the detection speed. 3. The image forming apparatus according to claim 1, wherein the sheet conveyance speed when the sheet position is detected is switched to the detection speed only when the image position high accuracy mode is selected. The paper position detecting means includes a light emitting portion and a light receiving portion, and the light emitting portion includes at least one light emitting element, and the light receiving portion includes a light receiving element array in which a plurality of light receiving elements are arranged in a line at substantially equal intervals. 4. The image forming apparatus according to claim 1, wherein an end of the sheet in the width direction is determined based on whether or not the light reception output of each light receiving element is equal to or greater than a threshold value. 5. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured as a copying machine, a printer, a facsimile machine, or a multifunction machine having at least two of these functions.

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