JP2009040541A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device capable of forming an image without any transfer deviation or wrinkle. <P>SOLUTION: A loop sensor 29 comprises a rotating body 31 having a gear-shaped section which is provided on one surface of a sheet P passing through conveying guide members 25, 27 in an abutting manner, and rotated following a loop of the sheet P, a supporting shaft 32 for turnably supporting the rotating body 31, and a rotation number sensor (a photo interrupter) 33 for detecting the number of rotation of the rotating body 31, and senses the loop of the sheet P based on the result of detection of the number of rotation of the rotating body 31 in the rotation number sensor 33. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus for forming an image on a sheet material by an electrophotographic method, and more particularly to an image forming apparatus capable of conveying a sheet material while maintaining an appropriate amount of a loop of the sheet material between a transfer unit and a fixing unit. .

  In an image forming apparatus using an electrophotographic system, after a toner image on a photoconductor is transferred to a sheet material at a transfer portion, the sheet material is guided to a nip portion of a fixing device through a conveyance guide portion. Here, when the leading edge of the sheet material has entered the nip portion of the fixing device, the trailing edge portion may not yet pass through the transfer portion.

  On the other hand, there may be a difference between the sheet material conveyance speed in the fixing device and the sheet material conveyance speed in the transfer unit due to thermal expansion, solid difference, or aging of the pressure roller provided in the fixing device. In such a case, if the sheet material conveyance speed in the fixing unit exceeds that of the transfer unit, a phenomenon occurs in which the sheet material carrying the unfixed toner image is pulled to the fixing unit side between the fixing unit and the transfer unit. There is a risk of shifting.

  In order to prevent the occurrence of such a transfer deviation phenomenon, it has been conventionally performed to form a slack (hereinafter referred to as “loop”) on a sheet material conveyed between a transfer portion and a fixing device. . However, if an excessive loop is given to the sheet material, wrinkles may be generated. Accordingly, it is desired to transport the sheet material while maintaining an appropriate loop amount of the sheet material between the transfer unit and the fixing device.

  One approach to meet these demands is to provide an independent drive system for each unit in an image forming apparatus that has a fixing unit and a transfer unit, and detect the upper and lower limits of the loop amount that forms on the paper before the fixing unit entrance. When the upper limit of the loop amount is detected, the speed of the driving unit on the fixing unit side is increased, and when the lower limit of the loop amount is detected, the speed of the driving unit on the fixing unit side is decreased. A technique for controlling the conveyance speed of a sheet material based on the loop amount is known (for example, see Patent Document 1).

  However, in the technique described in Patent Document 1, when a paper loop occurs, the loop is detected by always contacting the paper with a lever having a substantially square shape that is pivotally supported by the support shaft. Since the mechanism is adopted, it has not been said yet from the viewpoint of forming an image free from transfer displacement and wrinkles. That is, from the viewpoint of forming an image free from transfer deviation and wrinkles, it is required to make the contact area and contact time of the loop detection mechanism to the paper as small as possible. Such considerations are not made in technology. For this reason, from the viewpoint of forming an image free from transfer displacement and wrinkles, it has not been said yet.

JP-A-7-234604

  The problem to be solved is that the technique described in Japanese Patent Laid-Open No. 2004-228561 is still not enough from the viewpoint of forming an image free from transfer displacement and wrinkles, and there is room for improvement.

  The present invention provides an image carrier on which a toner image is carried for the purpose of forming an image free from transfer deviation and wrinkles, a transfer unit for transferring the toner image of the image carrier to a sheet material, A fixing unit for fixing a transfer toner image on the sheet material; a driving system provided independently for each of the transfer unit and the fixing unit; and the sheet material fed from the transfer unit by the driving system. An image forming apparatus including a conveyance guide member for guiding toward the fixing unit, the loop detection unit detecting a loop of the sheet material passing through the conveyance guide member, and the loop detection. Drive control means for performing drive control of the drive system based on the detection result of the means, wherein the loop detection means is a single member in the sheet material passing through the conveyance guide member. A rotating body having a gear-shaped cross section that rotates following the loop of the sheet material, a support shaft for rotatably supporting the rotating body, and the rotating body A rotational speed sensor for detecting the rotational speed of the sheet material, and detecting a loop of the sheet material based on a rotational speed detection result of the rotating body in the rotational speed sensor.

  An image forming apparatus according to the present invention includes an image carrier on which a toner image is carried, transfer means for transferring the toner image on the image carrier to a sheet material, and fixing the transferred toner image on the sheet material. Fixing means, a driving system provided independently for each of the transfer means and the fixing means, and conveyance for guiding the sheet material fed from the transfer means by the driving system toward the fixing means. An image forming apparatus comprising: a guide member; a loop detection unit that detects a loop of the sheet material that passes through the conveyance guide member; and a detection result of the drive system based on a detection result of the loop detection unit. Drive control means for performing drive control, wherein the loop detection means is provided so as to be able to contact one surface of the sheet material passing through the conveyance guide member, and the sheet A rotating body having a gear-shaped cross section, a support shaft for rotatably supporting the rotating body, and a rotational speed sensor for detecting the rotational speed of the rotating body And detecting the loop of the sheet material based on the rotation speed detection result of the rotating body in the rotation speed sensor. Therefore, in the conventional loop detection mechanism, when a loop occurs in the sheet material, Whereas the loop is detected by always contacting the paper with a substantially square-shaped lever rotatably supported on the support shaft, in the present invention, the contact area and the contact time are made possible. As a result, it is possible to detect a loop by rotating a rotating body having a gear-shaped cross section in contact with the one surface as the sheet material is conveyed in consideration of reducing the size of the sheet. As there is no transfer deviation or wrinkles It can contribute to the image formation.

  For the purpose of forming an image free from transfer deviation and wrinkles, the cross section is provided so as to be able to contact one surface of the sheet material passing through the conveyance guide member, and rotates following the loop of the sheet material. A gear-shaped rotating body, a support shaft for rotatably supporting the rotating body, and a rotation speed sensor for detecting the rotation speed of the rotating body, the rotating body in the rotation speed sensor This is realized by a loop detection means for detecting a loop of the sheet material on the basis of the rotation number detection result.

  Hereinafter, an image forming apparatus according to the present invention will be described in detail with reference to the drawings.

[Main Configuration of Image Forming Apparatus]
FIG. 1 is a block diagram of the main part of an image forming apparatus according to an embodiment of the present invention, and FIG.

  As shown in FIG. 1, the image forming unit 11 of the image forming apparatus according to the embodiment of the present invention conveys the sheet material P from the lower side to the upper side in the vertical direction. An electrophotographic photosensitive member 13 as an image carrier is disposed on the upstream side in the transport direction. This photosensitive member 13 is formed by forming an organic photosensitive layer on the outer peripheral surface of a conductive photosensitive substrate, and is rotated at a predetermined peripheral speed (process speed) in the clockwise direction indicated by an arrow in FIG. The photosensitive member 13 is primarily charged by a charger (not shown) to a predetermined polarity and potential, in this example, a predetermined negative potential in this example, during the rotation process. Laser scanning exposure of image information is performed on the photosensitive member charging surface by a laser scanner (not shown). As a result, the potential of the exposed bright portion of the photosensitive member charging surface is attenuated, and an electrostatic latent image corresponding to the scanning exposure pattern is formed. Next, the electrostatic latent image is developed as a developer image (hereinafter referred to as a toner image) by a developing device (not shown). In this example, the electrostatic latent image is reversely developed (negatively charged toner is attached to the exposed bright portion) with negative toner charged negatively.

  The toner images are sequentially transferred to a sheet material P fed from a paper feeding mechanism unit (not shown) at a transfer nip T which is a contact portion between the photosensitive member 13 and a transfer roller (transfer means) 15. Go. In the process in which the sheet material P is nipped and conveyed through the transfer nip portion T, a predetermined transfer bias is applied to the transfer roller 15 and the toner image on the surface of the photoreceptor 13 is sequentially electrostatically transferred onto the surface of the sheet material P. The

  The sheet material sent out from the transfer nip T is separated from the surface of the photoreceptor 13 and conveyed to a fixing device (fixing means) 17. The surface of the photoreceptor 13 after separation of the sheet material is subjected to repeated image formation after residual deposits such as transfer residual toner are removed and cleaned by a cleaner (not shown).

  The fixing device 17 is, for example, a heating device driven by a pressure rotator, and includes a fixing roller 21 and a pressure roller 23. A fixing nip portion N is formed between the fixing roller 21 and the pressure roller 23. In this fixing nip portion N, the unfixed toner image conveyed from the transfer nip portion T is melted and fixed by heating and pressing. Note that the fixing roller 21 and the pressure roller 23 are members having a longitudinal direction in FIG. The sheet material P that has passed through the fixing nip N is discharged and conveyed to a downstream mechanism.

  A pair of conveyance guide members 25 and 27 for guiding the conveyance of the sheet material P are arranged on the path from the transfer roller 15 to the fixing device 17 so as to face each other with the sheet material P interposed therebetween. Yes. The conveyance guide members 25 and 27 are provided with a loop sensor 29 for detecting a loop of the sheet material P. The loop sensor 29 is provided almost in the middle of the conveyance path of the sheet material P from the transfer nip T to the fixing nip N. This is because the loop amount of the sheet material P from the transfer nip T to the fixing nip N is considered to be the largest in the vicinity of the middle. Further, the loop sensor 29 is configured to detect a surface of the sheet material P that is different from the toner image forming surface when a certain amount of loop (for example, from the middle level to a little more than that) occurs. It is provided at an appropriate position in the conveyance guide member 27 that can come into contact (see the sheet material P indicated by a dotted line in FIG. 1). This is because if a certain amount of loop occurs in the sheet material P and this is detected and the detection result is fed back to the drive control system, it is considered that the loop of the sheet material P can be maintained in an appropriate amount. That is, the loop sensor 29 serves to detect a loop of the sheet material P.

  More specifically, as shown in FIGS. 1 and 2, the loop sensor 29 functioning as the loop detecting means of the present invention is a surface different from the toner image forming surface of the sheet material P passing through the conveyance guide members 25 and 27 ( (Corresponding to “one surface” in claim 1)) and a rotating body 31 that rotates following the loop of the sheet material P, and for rotatably supporting the rotating body 31. A support shaft 32, a rotation speed sensor 33 for detecting the rotation speed of the rotating body, and a loop detection unit 35 described later are provided.

  The rotating body 31 preferably has a gear-shaped cross section. This is because, when a loop occurs in the sheet material P, the contact area and the contact time with the sheet material P can be made as small as possible. The rotating body 31 is formed with an appropriate thickness in a direction (width direction) orthogonal to the conveying direction of the sheet material P. A plurality of rotating bodies 31 can also be provided in a direction (width direction) orthogonal to the conveying direction of the sheet material P.

  As the rotation speed sensor 33, a photo interrupter can be preferably used. When a photo interrupter is employed as the rotation speed sensor 33, the photo interrupter is provided at a position corresponding to the gear portion in the rotating body 31 and outputs a pulse signal corresponding to the rotation speed of the rotating body 31.

  The loop detection unit 35 plays a role of detecting a loop of the sheet material P based on the rotation speed detection result of the rotating body 31 in the rotation speed sensor. Note that the loop detection unit 35 operates so as to ignore the output pulse related to the initial movement among the pulse signals corresponding to the rotation speed of the rotating body 31 output from the photo interrupter as invalid. It is based on the possibility of causing a malfunction if the output pulse related to the initial movement is taken in as effective. Further, the loop detection unit 35 is configured to output a predetermined sheet material P out of pulse signals corresponding to the rotation speed of the rotating body 31 output from the photo interrupter after the initial motion pulse is output from the photo interrupter. The pulse signal generated within the expected time interval obtained based on the transport speed or the like operates so as to be captured as effective. This is because if such a configuration is adopted, malfunctions can be avoided in advance.

  The detection result in the loop detection unit 35 is given to a drive control unit (not shown) that performs drive control of a drive system such as the transfer roller 15, the fixing roller 21, or the pressure roller 23. As a result, the loop detection result obtained by the loop sensor 29 can be reflected in the drive control system.

[Operation of loop sensor]
FIG. 3 is a diagram showing the capture timing related to the pulse signal of the loop sensor according to the embodiment of the present invention.

  As shown in FIG. 3, in order to avoid malfunction, the loop detection unit 35 invalidates the output pulse related to the initial motion out of the pulse signal corresponding to the rotation speed of the rotating body 31 output from the photo interrupter. Ignore it as a bad thing. Further, after a pulse related to the initial movement is output from the photo interrupter, based on a predetermined conveyance speed of the sheet material P among pulse signals corresponding to the rotation speed of the rotating body 31 output from the photo interrupter. Pulse signals that occur within the expected time interval obtained are captured as valid. Specifically, for example, only a pulse signal generated after a lapse of a certain time since the detection of the pulse output related to the initial movement is taken in as valid. The timing time of the expected time interval related to the capture is appropriately determined based on the conveyance speed of the sheet material P and the number of teeth of the rotation body 31 because the conveyance speed of the sheet material P and the angular speed of the rotation body 31 are almost the same. can do.

  Specifically, for example, after a pulse related to the initial motion is output from the photo interrupter, the sheet material P is generated when an effective pulse signal is generated several times continuously within an expected time interval related to capture. Is continuously in contact with the rotating body 31. In this case, since the rotation speed of the fixing roller 23 is delayed with respect to the conveyance speed, the rotation speed of the fixing roller 23 is increased by a predetermined amount. In this way, it is possible to avoid an excessive amount of loop of the sheet material P in advance.

[Effect of Example]
As described above, in the image forming apparatus according to the embodiment of the present invention, the loop sensor 29 is provided so as to be in contact with one surface of the sheet material P passing through the conveyance guide members 25 and 27, and A rotating body 31 that rotates following the loop and has a gear-shaped cross section, a support shaft 32 for rotatably supporting the rotating body 31, and a rotational speed for detecting the rotational speed of the rotating body 31 Sensor (photo interrupter) 33, and the loop of the sheet material P is detected based on the rotation number detection result of the rotating body 31 in the rotation number sensor 33. Therefore, in the conventional loop detection mechanism, the loop is added to the sheet material. In the present invention, a loop is detected by always contacting a paper having a substantially U-shaped lever pivotally supported on a support shaft to the paper. And contact In consideration of making the gap as small as possible, the rotating body 31 having a gear-shaped cross section detects a loop by rotating while abutting against the one surface as the sheet material P is conveyed. As a result, it is possible to contribute to image formation free from transfer displacement and wrinkles. Furthermore, a high-accuracy loop detection result performed at an appropriate timing is given to a drive control means (not shown) that performs drive control of a drive system such as the transfer roller 15, the fixing roller 21, or the pressure roller 23. it can. As a result, the sheet material P can be conveyed while maintaining an appropriate amount of the loop of the sheet material P passing through the conveyance guide members 25 and 27 through reflecting a highly accurate loop amount in the drive control system. This can contribute to image formation free from transfer deviation and wrinkles.

[Others]
The present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the gist of the invention read from the claims and the entire specification or the technical idea, and image formation accompanied by such changes The apparatus is also included in the scope of the technical scope of the present invention.

  That is, in the embodiment of the present invention, the image forming unit 11 that conveys the sheet material P from the lower side to the upper side in the vertical direction is exemplified and described. However, the present invention is not limited to such an embodiment. The present invention can be applied as it is to the image forming unit 11 in any aspect such as the conveyance direction of the sheet material P being the horizontal direction or the oblique direction.

  In the embodiment of the present invention, the electrophotographic photosensitive member is exemplified and described as the image carrier. However, the present invention is not limited to the embodiment, and a transfer belt is employed instead of the photosensitive member. It goes without saying.

1 is a configuration diagram of a main part of an image forming apparatus according to an embodiment of the present invention. It is a whole lineblock diagram of a loop sensor which functions as a loop detection means of the present invention. It is a figure which shows the taking-in timing which concerns on the pulse signal of the loop sensor which concerns on an Example of this invention.

Explanation of symbols

11 Image forming unit 13 Photosensitive member (image carrier)
15 Transfer roller (transfer means)
17 Fixing device (fixing means)
21 Fixing roller (fixing means)
23 Pressure roller (fixing means)
25, 27 A pair of conveyance guide members 29 Loop sensor (loop detection means)
31 Rotating body 32 Support shaft 33 Rotational speed sensor (Photo interrupter)
35 Loop detector P Sheet material

Claims (4)

An image carrier on which a toner image is carried, a transfer unit for transferring the toner image of the image carrier to a sheet material, a fixing unit for fixing a transfer toner image of the sheet material, and the transfer unit; A drive system provided independently for each of the fixing means; and a conveyance guide member for guiding the sheet material fed from the transfer means by the drive system toward the fixing means. An image forming apparatus comprising:
Loop detection means for detecting a loop of the sheet material passing through the conveyance guide member;
Drive control means for performing drive control of the drive system based on the detection result of the loop detection means;
Further comprising
The loop detection means includes
A rotating body that is provided so as to be able to contact one surface of the sheet material passing through the conveyance guide member and rotates following the loop of the sheet material.
A support shaft for rotatably supporting the rotating body;
A rotational speed sensor for detecting the rotational speed of the rotating body;
With
An image forming apparatus, comprising: detecting a loop of the sheet material based on a rotation number detection result of the rotating body in the rotation number sensor. The image forming apparatus according to claim 1,
The rotation speed sensor is configured by a photo interrupter,
In this case, the photo interrupter is provided at a position corresponding to the gear portion of the rotating body, and outputs a pulse signal corresponding to the rotational speed of the rotating body. The image forming apparatus according to claim 2,
Among the pulse signals corresponding to the rotation speed of the rotator output from the photo interrupter, an output pulse related to the initial motion is ignored as invalid and the image forming apparatus. The image forming apparatus according to claim 3, wherein
After a pulse related to the initial movement is output from the photo interrupter, based on a predetermined conveyance speed of the sheet material among pulse signals corresponding to the rotation speed of the rotating body output from the photo interrupter. An image forming apparatus characterized in that a pulse signal generated within an estimated expected time interval is captured as effective.

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