JP4973518B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, particularly an image forming apparatus that employs a tandem method, conveys a sheet at a nip formed by an image carrier and a transfer member, and forms a color image or a monochrome image on the sheet. About.

  2. Description of the Related Art Conventionally, in a tandem color image forming apparatus using Y, M, C, and Bk image forming units, a single color image formed on each photoreceptor is superposed on an intermediate transfer belt and then a sheet There are known an indirect transfer method in which transfer is performed on top and a direct transfer method in which transfer is performed on a sheet conveyed on a belt (Patent Documents 1 and 2). In addition, priority is given to the freedom of arrangement of image forming units, etc. and cost reduction, and toner is transferred onto the paper while transporting the paper at the nip formed by the pair of the photoconductor and the transfer roller without using a belt. There is also known a beltless direct transfer method for transferring to a belt (Patent Document 3).

A tandem image forming apparatus forms a color image, but often forms a monochrome image, and also rotates the photoreceptors of Y, M, and C image forming units that are not used in forming a monochrome image. In addition, there is a problem that the photoconductor and toner deteriorate.
JP-A-8-328395 JP 2007-34085 A JP 7-319254 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus that employs a tandem system and a beltless direct transfer system that can suppress deterioration of a photoconductor and toner as much as possible.

In order to achieve the above object, the present invention provides:
A plurality of pairs of an image carrier and a transfer member that transfers toner on the image carrier onto the paper are provided, the paper is conveyed at a nip formed by the image carrier and the transfer member, and the color is printed on the paper. In an image forming apparatus that forms an image or a monochrome image,
Contact / separation means for pressing / separating the image carrier or the transfer member from each other;
Control means for separating a pair of an image carrier and a transfer member that are not necessary for transporting a sheet during monochrome image formation;
It is provided with.

  In the image forming apparatus according to the present invention, when the monochrome image is formed, the pair of the image carrier and the transfer member which are not necessary for transporting the paper is separated, so that the driving of the image carrier unnecessary for transporting the paper is stopped. The deterioration of the image carrier, the toner, or the transfer member can be suppressed as much as possible.

  In the image forming apparatus according to the present invention, a roller can be suitably used as the transfer member. The control unit may be capable of changing the timing of separating the pair of the image carrier and the transfer member, which are not necessary for the conveyance of the sheet during monochrome image formation, according to the length of the sheet conveyance direction. Further, the pair of the image carrier and the transfer member that are not necessary for the conveyance of the sheet may be pressed / separated at a predetermined timing from the upstream side in the conveyance direction of the sheet.

  Further, the apparatus includes a detection unit for the conveyed paper and a detection unit for the conveyance speed of the paper, and the control unit is based on information from the paper detection unit and the conveyance speed detection unit. The pair may be pressed / separated.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings. Note that, in each embodiment, the same members and parts are denoted by the same reference numerals, and redundant descriptions are omitted.

(Schematic configuration of image forming apparatus, see FIG. 1)
FIG. 1 shows an embodiment of an image forming apparatus according to the present invention. In this image forming apparatus, image forming units 10Y, 10M, 10C, and 10Bk for forming images of Y (yellow), M (magenta), C (cyan), and Bk (black) are sequentially arranged from the lower stage to the upper stage. It is a thing. Each of the image forming units 10Y, 10M, 10C, and 10Bk includes photosensitive drums 11Y, 11M, 11C, and 11Bk, developing units 12Y, 12M, 12C, and 12Bk, a charging charger (not shown), and the like. Transfer rollers 13Y, 13M, 13C, and 13Bk that are paired with the photosensitive drums 11Y, 11M, 11C, and 11Bk are disposed so as to face each other.

  In the image forming units 10Y, 10M, 10C, and 10Bk, the sheet is conveyed upward at a nip portion formed by the photosensitive drums 11Y, 11M, 11C, and 11Bk and the transfer rollers 13Y, 13M, 13C, and 13Bk. Note that the sheet conveyance path here is slightly curved as shown by a dotted line in FIG.

  The laser scanning optical unit 15 emits a laser beam based on the image data from the gaps between the image forming units 10Y, 10M, 10C, and 10Bk to the photosensitive drums 11Y, 11M, 11C, and 11Bk, and electrostatic latent An image is formed. Note that this type of image forming process is well known, and a detailed description thereof will be omitted.

  A plurality of sheets are housed in a stacked state in the automatic sheet feeding tray 20 and are fed one by one upward. When the color image is formed while being conveyed through the conveyance path, the photosensitive drums 11Y, 11M, 11C, A yellow, magenta, cyan, and black image is transferred from 11Bk, and a black image is transferred from the photosensitive drum 11Bk when a monochrome image is formed. After the image is transferred, the paper is fixed with toner by the fixing unit 30 and is discharged from the pair of discharge rollers 31 onto the tray 32.

  Further, a contact / separation means (not shown) is provided on each of the transfer rollers 13Y, 13M, 13C, 13Bk to press / separate the photosensitive drums 11Y, 11M, 11C, 11Bk. The contact / separation means is composed of a solenoid or a rotating cam and is controlled by a control unit (CPU) 40 for overall control of the image forming apparatus.

  At the time of color image formation, the transfer rollers 13Y, 13M, 13C, and 13Bk are pressed against the photosensitive drums 11Y, 11M, 11C, and 11Bk, and the image forming units 10Y, 10M, 10C, and 10Bk are driven, and the paper is The photosensitive drums 11Y, 11M, 11C, and 11Bk that are driven to rotate and the transfer rollers 13Y, 13M, 13C, and 13B that are driven to rotate are conveyed at a nip portion.

  On the other hand, at the time of forming a monochrome image, the transfer roller 13Bk for forming a black image is always in pressure contact with the photosensitive drum 11Bk, and the transfer rollers 13Y, 13M, and 13C for forming a color image are not necessary for conveying the paper. Those are selectively separated from the photosensitive drums 11Y, 11M, and 11C, and the rotation of the photosensitive drum from which the transfer roller is separated is stopped. The first, second and third embodiments relating to the control during monochrome image formation will be described below.

(See the first embodiment, FIG. 2)
FIG. 2 schematically shows the operation of the first embodiment. In the transport path, transport roller pairs 16 and 17 are disposed on the upstream side in the transport direction A, and transport roller pair 18 is disposed on the downstream side. ing. In the first embodiment, the length in the transport direction of the sheet S is longer than the interval from the most upstream photoreceptor drum 11Y to the most downstream photoreceptor drum 11Bk.

  In the first embodiment, at the time of monochrome image formation, the photosensitive drums 11M and 11Bk are always driven to rotate, and the transfer rollers 13M and 13Bk are always in pressure contact. On the other hand, the photosensitive drums 11Y and 11C are stopped from rotating and the transfer rollers 13Y and 13C are separated. Therefore, as shown in FIG. 2A, the sheet S is delivered from the conveying roller pair 17 to the nip portion between the photosensitive drum 11M and the transfer roller 13M. Further, as shown in FIG. 2B, the black image is transferred while being conveyed at the nip portion between the photosensitive drum 11Bk and the transfer roller 13Bk. Thereafter, the sheet is conveyed by the conveying roller pair 18.

  With the above control, when forming a monochrome image, the pair of the photosensitive drum and the transfer roller which are not necessary for transporting the paper is separated and the rotation of the photosensitive drum is stopped. Roller deterioration can be suppressed as much as possible.

(Refer to the second embodiment, FIG. 3)
FIG. 3 schematically shows the operation in the second embodiment. Similar to the first embodiment, the length of the sheet S in the transport direction is from the most upstream photoreceptor drum 11Y to the most downstream photoreceptor drum 11Bk. This is a case where the interval is longer than. In the second embodiment, the contact / separation of the transfer rollers 13Y, 13M, 13C, and 13Bk is controlled in time series during monochrome image formation. For this purpose, a sensor 21 for detecting the paper S is provided between the conveying roller pair 17 and the photosensitive drum 11Y, and an encoder 22 for detecting the rotational speed of the photosensitive drum 11Y is provided. Information of the sensor 21 and the encoder 22 is input to the control unit 40, and the progress state of the paper S is detected. The photosensitive drums 11Y, 11M, 11C, and 11Bk are all driven to rotate at the same speed.

  In the second embodiment, the photosensitive drum 11Bk is always driven to rotate and the transfer roller 13Bk is always in pressure contact during monochrome image formation. The photosensitive drums 11Y, 11M, and 11C are stopped rotating and the transfer rollers 13Y, 13M, and 13C are separated until the sheet S is conveyed.

  When the leading edge of the sheet S is detected by the sensor 21, the photosensitive drum 11Y is rotationally driven and the transfer roller 13Y comes into pressure contact with the photosensitive drum 11Y. Thus, as shown in FIG. 3A, the sheet S is conveyed by the photosensitive drum 11Y and the transfer roller 13Y. The photosensitive drums 11M and 11C are driven to rotate and the transfer rollers 13M and 13C are moved to the photosensitive drum according to the conveyance state of the paper S, that is, whenever the leading edge of the paper S reaches immediately before the photosensitive drums 11M and 11C. Press contact with 11M and 11C. Thus, as shown in FIGS. 3B and 3C, the sheet S is conveyed by the photosensitive drums 11M and 11C and the transfer rollers 13M and 13C.

  Thereafter, the sheet S is conveyed by the photosensitive drum 11Bk and the transfer roller 13Bk, and the black image is transferred. At the same time, the transfer rollers 13Y and 13M are separated from the photosensitive drums 11Y and 11M, and the rotation of the photosensitive drums 11Y and 11M is stopped (see FIG. 3D). Further, when the sheet S is conveyed by the conveying roller pair 18, the transfer roller 13C is separated from the photosensitive drum 11C, and the rotation of the photosensitive drum 11C is stopped (see FIG. 3E).

  With the above control, when a monochrome image is formed, a pair of the photosensitive drum and the transfer roller that are not necessary for transporting the paper is brought into contact with and separated at a predetermined timing, and the rotation of the photosensitive drum separated from the transfer roller is stopped. It is possible to suppress deterioration of the photoreceptor and toner or transfer roller as much as possible.

(Refer to the third embodiment, FIG. 4)
In the third embodiment, when a monochrome image is formed, the timing at which the pair of the photosensitive drum and the transfer roller, which is not necessary for the conveyance of the sheet, is brought into contact with and separated from the sheet is changed according to the length of the sheet conveyance direction. In this case, the pair of the photosensitive drum and the transfer roller is pressed / separated at a predetermined timing from the upstream side in the sheet conveyance direction.

  As shown in FIG. 4, the pair of the photoconductive drum and the transfer roller is arranged at a position of N1 to N4, and the pair of conveying rollers 17 and 18 are arranged at a predetermined interval L at the illustrated positions. As shown in Tables 1A to 1D below, the sheet length in the conveyance direction A is length 1: less than (L + α) to (2L + α), length 2: less than (2L + α) to (3L + α), and long. The control is divided into four types of length 3: (3L + α) to less than (4L + α) and length 4: 4L + α or more. Further, a pair of a photosensitive drum and a transfer roller for forming a black image is arranged in any one of N1 to N4. The control when arranged in N1 is shown in Table 1A and arranged in N2. The case is shown in Table 1B, the case of being arranged in N3 is shown in Table 1C, and the case of being arranged in N4 is shown in Table 1D.

  Specifically, when the black image forming photosensitive drum and transfer roller pair are arranged at N1, as shown in Table 1A, if the paper length is 1, the photosensitives located at N1 to N4 are arranged. All pairs of the body drum and the transfer roller are brought into a pressure contact state, and all the photosensitive drums are rotationally driven. If the sheet length is 2, the pair of the photosensitive drum and the transfer roller positioned at N1 and N3 is brought into a pressure contact state, and the photosensitive drum is driven to rotate. If the sheet length is 3, the pair of the photosensitive drum and the transfer roller located at N1 and N4 is brought into a pressure contact state, and the photosensitive drum is driven to rotate. If the sheet length is 4, only the pair of the photosensitive drum and the transfer roller positioned at N1 is brought into a pressure contact state, and the photosensitive drum is driven to rotate.

  When the pair of the photosensitive drum for black image formation and the transfer roller is arranged at N2, as shown in Table 1B, if the paper length is 1, the photosensitive drum and the transfer roller located at N1 to N4 All of the photosensitive drums are rotationally driven by bringing all the pairs to the pressure contact state. If the sheet length is 2, the pair of the photosensitive drum and the transfer roller located at N2 and N4 is brought into a pressure contact state, and the photosensitive drum is driven to rotate. If the paper length is 3 and the paper length is 4, only the pair of the photosensitive drum and the transfer roller located at N2 is brought into a pressure contact state, and the photosensitive drum is rotationally driven.

  When the pair of the photosensitive drum for black image formation and the transfer roller is arranged at N3, as shown in Table 1C, if the paper length is 1, the photosensitive drum and the transfer roller located at N1 to N4 All of the photosensitive drums are rotationally driven by bringing all the pairs to the pressure contact state. If the sheet length is 2, the pair of the photosensitive drum and the transfer roller positioned at N1 and N3 is brought into a pressure contact state, and the photosensitive drum is driven to rotate. If the paper length is 3 and the paper length is 4, only the pair of the photosensitive drum and the transfer roller located at N3 is brought into a pressure contact state, and the photosensitive drum is rotationally driven.

  When a pair of the photosensitive drum for black image formation and the transfer roller is arranged at N4, as shown in Table 1D, if the paper length is 1, the photosensitive drum and the transfer roller located at N1 to N4 All of the photosensitive drums are rotationally driven by bringing all the pairs to the pressure contact state. If the sheet length is 2, the pair of the photosensitive drum and the transfer roller located at N2 and N4 is brought into a pressure contact state, and the photosensitive drum is driven to rotate. If the sheet length is 3, the pair of the photosensitive drum and the transfer roller located at N1 and N4 is brought into a pressure contact state, and the photosensitive drum is driven to rotate. If the sheet length is 4, only the pair of the photosensitive drum and the transfer roller located at N4 is brought into a pressure contact state, and the photosensitive drum is rotationally driven.

  With the above control, when forming a monochrome image, the pair of the photosensitive drum and the transfer roller that are not necessary for transporting the paper is separated and the rotation of the photosensitive drum separated from the transfer roller is stopped. It is possible to suppress deterioration or transfer roller deterioration as much as possible.

(Other examples)
Note that the image forming apparatus according to the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the gist thereof.

  In particular, the basic configuration of the image forming apparatus is arbitrary, and may be a printer, a copier, or a function such as a facsimile. Further, the transfer member may be a belt-like member other than the roller.

1 is an overall schematic configuration diagram of an image forming apparatus according to the present invention. It is explanatory drawing which shows typically the operation | movement in 1st Example. It is explanatory drawing which shows typically the operation | movement in 2nd Example. It is explanatory drawing which shows arrangement | positioning of the photoconductive drum and transfer roller in 3rd Example.

Explanation of symbols

10Y, 10M, 10C, 10Bk ... Image forming unit 11Y, 11M, 11C, 11Bk ... Photosensitive drum 13Y, 13M, 13C, 13Bk ... Transfer roller 40 ... Control unit A ... Paper transport direction S ... Paper

Claims (5)

A plurality of pairs of an image carrier and a transfer member that transfers toner on the image carrier onto the paper are provided, the paper is conveyed at a nip formed by the image carrier and the transfer member, and the color is printed on the paper. In an image forming apparatus that forms an image or a monochrome image,
Contact / separation means for pressing / separating the image carrier or the transfer member from each other;
Control means for separating a pair of an image carrier and a transfer member that are not necessary for transporting a sheet during monochrome image formation;
An image forming apparatus comprising:   2. The control unit according to claim 1, wherein the timing of separating the pair of the image carrier and the transfer member, which is not necessary for the conveyance of the sheet at the time of monochrome image formation, can be changed according to the length of the sheet conveyance direction. The image forming apparatus described.   2. The control unit according to claim 1, wherein the control unit presses / separates a pair of an image carrier and a transfer member that are not necessary for paper conveyance at a predetermined timing from the upstream side in the paper conveyance direction during monochrome image formation. Image forming apparatus. Furthermore, a detection unit for the conveyed paper and a detection unit for the conveyance speed of the paper are provided,
The control means presses / separates a pair of an image carrier and a transfer member which are not necessary for paper conveyance based on information from the paper detection means and conveyance speed detection means;
The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the transfer member is a roller.

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