JP4365542B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and more particularly to an image forming apparatus provided with a developing device having a plurality of developing units that store developers of different colors.
[0002]
[Prior art]
Image forming apparatus such as a copying machine, a facsimile machine, a printer, etc., which obtains a multi-color image by using a developing device in which a developing device containing a developer and a developing sleeve for conveying the developer is arranged around an image carrier made of a photosensitive member For example, the following conventional techniques exist.
[0003]
(1) A method of obtaining a multi-color image by forming a plurality of visible images on an image carrier by a plurality of developing means is disclosed in JP-A-5-142918, JP-A-6-324571, and JP-A-2000-. No. 172043.
[0004]
In these image forming apparatuses, since it is not necessary to provide an intermediate transfer member, the apparatus can be reduced in size and cost, and a plurality of latent image forming means corresponding to each of a plurality of developing apparatuses can be provided. It is possible to form a multi-color image without rotating the body a plurality of times, and the apparatus speed can be increased.
[0005]
However, when a visible image of the second color or later is formed on the photosensitive member, the developer on the developing sleeve is not in contact with the photosensitive member in order to avoid affecting the visible image already formed on the photosensitive member. Develop in contact. Further, a developing method that hardly affects the visible image on the photosensitive member by devising the waveform of the AC voltage of the developing bias that is essential for non-contact development and the magnetic pole arrangement of the magnet in the developing roller is disclosed.
[0006]
However, since charging, exposure, and development are repeated on the visible image formed on the photoconductor, deterioration of the visible image formed on the photoconductor cannot be completely avoided. It is difficult to obtain an image.
[0007]
(2) On the other hand, there is a system in which a visible image formed on an image carrier by a plurality of developing means is sequentially transferred onto an intermediate transfer member and a multi-color image is formed on the intermediate transfer member. -216337, JP-A-5-333701, and JP-A-11-338257.
[0008]
In these image forming apparatuses, since only a single color visible image is formed on the image carrier, there is no image deterioration factor as in the above-described method, and high image quality is possible. Since it is necessary to provide an intermediate transfer member as compared with the method, the apparatus becomes large and expensive, and in order to form a multi-color image, the intermediate transfer member needs to be rotated a plurality of times. Speeding up is difficult.
[0009]
Further, developing means other than the developing means currently developing the latent image on the image carrier need to be in a non-contact state with respect to the image carrier. This is to prevent a developing device other than the developing device currently developing the latent image on the image carrier from affecting the latent image and the visible image on the image carrier. As a specific method, other than the method of retracting the developing device other than the developing device currently developing the latent image on the image carrier from the developing position, which is cited as the most reliable method, from the developing roller in the developing device. A method of cutting the ears of a magnetic brush on a developer carrier is disclosed.
[0010]
First, in Japanese Patent Laid-Open No. 5-216337, a schematic configuration diagram of a copying apparatus of the above-described type is shown in FIG. 1, an enlarged view around a photosensitive intermediate transfer belt is shown in FIG. FIG. 4 and FIG. 4 show a method of removing the developer from the surface of the developing roller by rotating the developing roller in the direction opposite to that during development. Paragraph No. [0039] and FIG. A method for reducing the developer on the developing roller by moving the position of the magnetic shielding plate so as to be movable in the roller except during development. Paragraph No. [0048] and FIG. A method is disclosed that is configured to be rotatable about an axis and moves the position of the developer on the developing roller to a position where it does not contact the photoreceptor except during development.
[0011]
In Japanese Patent Application Laid-Open No. 11-338257, a sleeve and a magnet that can rotate around the central axis of the sleeve are disposed upstream of the developing position of the developing roller, and the magnet is rotated to the developing position. A method of switching between introduction / blocking of developer is disclosed.
[0012]
Japanese Patent Laid-Open No. 5-333701 discloses a problem caused by a very small amount of developer that cannot be completely removed in a method in which the photosensitive member and the developer are brought into non-contact by removing the developer amount on the developing roller. A method is disclosed in which the developer on the developing roller is removed by rotating the developing roller magnet after the developer is removed.
[0013]
(3) An image forming apparatus that sequentially transfers a visible image formed on an image carrier by a plurality of developing means onto an intermediate transfer member to form a multi-color image on the intermediate transfer member, other than those described above. In addition, a plurality of image forming units each having a latent image forming unit and a plurality of developing units arranged around the image carrier are provided, and visible images formed by the respective image forming units are sequentially transferred onto a single intermediate transfer member. Japanese Patent Application Laid-Open No. 10-177286, Japanese Patent Application Laid-Open No. 11-44982, and Japanese Patent Application Laid-Open No. 2000-242058 disclose an apparatus for obtaining a multi-color image by superimposing and transferring images to each other.
[0014]
Since these image forming apparatuses form only a single-color visible image on the image carrier in the same manner as the above-described method, there is no image deterioration factor as in the above-described method, and high image quality is possible. is there. In the case of forming a full-color image of four colors, in the method using the single image carrier and intermediate transfer member described in (2) above, it is necessary to arrange four developing means around the image carrier. In the image forming apparatus (3), there are two developing means arranged around the image carrier, and the intermediate transfer member is rotated twice. Therefore, it is possible to reduce the size / diameter of the image carrier and speed up the apparatus.
[0015]
In the above-described methods (1) and (2) for forming a multi-color image on a single image carrier, it is necessary to dispose four developing means around the image carrier, and While the circumference of the carrier needs to be larger than the maximum output sheet length, in the image forming apparatus of (3), there are two developing means arranged around the image carrier, and the circumference of the image carrier is Since there is no restriction due to the length of the output paper, the image carrier can be significantly reduced in size / diameter.
[0016]
  thisThe thirdTechnologyBase ofDetails of this operation are described in paragraphs [0016] to [0031] of Japanese Patent Laid-Open No. 10-177286. Japanese Patent Laid-Open No. 11-44982 discloses a method and configuration for removing the developer from the surface of the developing roller except during development by changing the rotation direction of the developing roller to reverse to that during development. The publication discloses a method and configuration in which the developer on the developing roller and the photosensitive member are always in a non-contact state by employing non-contact development, and the developing means is switched by turning on / off the developing bias.
[0017]
As described above, in a method in which a visible image formed on an image carrier by a plurality of developing means is sequentially transferred onto an intermediate transfer member to form a multi-color image on the intermediate transfer member, Various methods for making developing means other than the developing means currently developing the latent image in a non-contact state with respect to the image carrier have been disclosed, but they have the following problems.
[0018]
Regarding the method for bringing the developing device into and out of contact with the image carrier, which is cited as the most reliable method, it requires a means for supporting the contact and separation, a contact and separation drive means, and a space for contact and separation, which complicates the apparatus. The increase in size and cost is unavoidable, and at the same time, there is a problem that the driving force transmission mechanism for the developing roller of the developing means and the developer stirring / conveying member is complicated and large.
[0019]
Further, as disclosed in JP-A-5-216337 and JP-A-5-333701, the developer on the developing roller is removed in a method in which the rotation direction of the developing roller is reverse to that during development. For this reason, it is necessary to rotate the developing roller for a certain period of time, and during this time, a visible image cannot be formed on the image carrier.
[0020]
In addition, when driving a plurality of developing rollers with a single motor to reduce the size of the apparatus, it is necessary to perform a driving force transmission switching operation after stopping the rotation of the developing roller. Since the operation is performed, the time during which a visible image cannot be formed on the image carrier is increased, which hinders speeding up.
[0021]
In the method of providing the developer introduction / interruption switching mechanism disclosed in JP-A-5-216337 and JP-A-11-338257, the developing roller is removed for a certain period of time in order to remove the developer on the developing roller. Therefore, the introduction / shutoff switching mechanism must be provided, so that the apparatus is complicated, large, and expensive.
[0022]
Further, regarding the method of moving the developing roller on the developing roller to the position where it does not come into contact with the photosensitive member by the rotation of the magnet in the developing roller in JP-A-5-216337, the developer on the developing roller is removed. However, a considerable amount of developer exists at the position facing the photosensitive member on the developing roller even if it does not contact the photosensitive member, and a sufficient separation distance between the developer and the photosensitive member cannot be secured. .
[0023]
For this reason, when a so-called scumming toner other than the toner necessary for forming a visible image is adhered on the photoconductor, the ground on the photoconductor is placed on the developing roller other than the developing means that is developing. Dirty toner is mixed. In addition, since the electric field is emphasized near the boundary between the exposed area and the non-exposed area in the latent image on the photoreceptor, the toner adheres to the boundary from the developing roller other than the developing unit that is developing due to the so-called edge effect. To do. For this reason, color mixing occurs in the image in the developing device or on the image carrier, which causes a reduction in image quality.
[0024]
As described in Japanese Patent Application Laid-Open No. 2000-242058, by adopting a non-contact development method, there is no need to provide a means for removing the developer on the developing roller, and development means other than the developing means being developed can be provided. The same occurs in the technique for bringing the image carrier into a non-contact state. In the non-contact development method, development is performed in a non-contact state between the developer and the photoconductor, but in order to achieve high image quality, the smaller the distance between the photoconductor and the developing roller, the so-called development gap, is more advantageous. For this reason, a sufficient separation distance between the developer and the photosensitive member cannot be secured, and the same problem occurs.
[0025]
[Problems to be solved by the invention]
The present invention has been made in view of these problems. A visible image formed on an image carrier by a plurality of developing means is sequentially transferred onto an intermediate transfer member, and a plurality of colors are formed on the intermediate transfer member. In an image forming apparatus that forms an image, even if the separation distance between the developing means other than the developing means that is developing and the image carrier is in a non-contact state, color mixing can be reliably prevented and image quality can be ensured. In addition, image formation that allows development means other than the development means being developed to be in a non-contact state with respect to the image carrier in a short time without incurring apparatus complexity, size increase, and cost increase. An object is to realize an apparatus.
[0026]
[Means for Solving the Problems]
  In order to achieve the object, the present invention has the following configuration.
  TimesA plurality of developing devices for developing a latent image on the image carrier configured to be rollable are arranged around the image carrier along the rotation direction of the image carrier, and one development in the plurality of developing devices When the apparatus is in the developing state, the other developing apparatuses are controlled to be in the non-developing state, and the image forming apparatus that performs multicolor development by sequentially changing the developing apparatus in the developing state to another developing apparatus The visible image developed by the developing device in the developing state passes through the developing device in the non-developing state disposed downstream of the developing device in the developing state in the rotation direction of the image carrier. Developing device arranged on the downstream side in the rotation directionThe potential V1 satisfies the following condition (1), and when a plurality of non-development developing devices are arranged downstream of the developing device in the developing state, the developing state is set. While a visible image developed in a certain developing device passes, the potential V1 ′ of an arbitrary developing device among the plurality of downstream developing devices, the potential V1 of a developing device arranged on the downstream side of the arbitrary developing device. '' Satisfies the following condition (2)did.
(1) When VB <VD, V1 <VD, and when VB> VD, V1> VD. (2) When VB <VD, V1 ′> V1 ″, and when VB> VD, V1 ′ <V1 ″. However, VB is the potential of the developing device in the developing state, and is only the DC component when an alternating electric field is applied. VD is the potential of the image portion of the latent image (the portion where the toner adheres).
[0039]
DETAILED DESCRIPTION OF THE INVENTION
A configuration of an image forming apparatus to which the present invention can be applied will be described.
FIG. 1 shows the configuration of an image forming apparatus to which the present invention is applied. The developing rollers 101 and 201 in the first developing unit I will be described in the examples of FIGS. 3, 5, 6, and 7 to be described later. The examples of FIGS. 3, 5, 6, and 7 are also described in the second developing unit II. It shall be based on.
[0040]
In FIG. 1, the intermediate transfer belt 10 is stretched between a driving roller 13 and a driven roller 12, and is driven by the driving roller 13 to travel in the direction of arrow a. The intermediate transfer belt 10 is given an optimum tension by a tension roller 60. On the lower running surface of the intermediate transfer belt 10, the first image forming unit I and the second image forming unit II are arranged at a constant interval along the running direction of the intermediate transfer belt 10. . The intermediate transfer belt 10 is longer by the non-image area than the length in the moving direction of the maximum size transfer paper used in the image forming apparatus of this embodiment.
[0041]
The first image forming unit I includes a photosensitive drum 16 as an image carrier and a charger 17 including a roller for uniformly charging the surface of the photosensitive drum 16 disposed around the photosensitive drum 16. And a writing unit 18 for writing on the charged surface of the photosensitive drum 16 with a beam modulated by an image signal, an A color developing unit 100, a C color developing unit 200, and a cleaning unit 20.
[0042]
The A color developing device 100 includes a developing roller 101, a paddle roller 102, a screw conveyor 103, and a developer supply port 104. The paddle roller 102 has screw-like fins 102 a, rotates in one direction, agitates the developer in the A color developing device 100 while conveying it in the axial direction, and supplies the developer to the developing roller 101.
[0043]
The screw conveyor 103 conveys the developer in the A color developing device 100 in a direction opposite to the conveyance direction by the paddle roller 102. The developer in the A color developing device 100 is supplied to the developing roller 101 in a state of being sufficiently stirred by the paddle roller 102 and the screw conveyor 103.
[0044]
A toner replenishing container (not shown) is detachably attached to the developer replenishing port 104, and the A color toner is replenished to one end of the screw conveyor 103 as needed, and the developer in the A color developing device 100 is replenished. The density is held at a predetermined value. The C color developing device 200 has the same configuration and function as the developing roller 101, paddle roller 102, screw conveyor 103, and developer supply port 104 of the A color developing device 100. The developing roller 201, the paddle roller 202, the screw conveyor 203, and the developing An agent supply port 204 is provided.
[0045]
As shown in FIG. 2, the paddle roller 102 and the screw conveyor 103 in the A color developing device 100 are gears 102G fixed to their respective shafts 102S and 103S on the outside of one end plate of the A color developing device 100. , 103G are connected to each other via an intermediate idler gear 10G. Similarly, the paddle roller 102 and the developing roller 101 are connected to each other via intermediate play gears by gears 102G and 101G fixed to their respective shafts 102S and 101S.
[0046]
As shown in FIG. 2, the paddle roller 202 and the screw conveyor 203 in the C-color developing device 200 are connected to each other through intermediate play gears 20G by gears 202G and 203G fixed to their respective shafts 202S and 203S. Yes.
[0047]
Similarly, the paddle roller 202 and the developing roller 201 are connected to each other via intermediate play gears by gears 202G and 201G fixed to their respective shafts 202S and 201S.
[0048]
Each of the developing rollers 101 and 201 is rotated in the direction of an arrow by driving the gears 103G and 203G of each screw conveyor by a driving source.
[0049]
In FIG. 2, a drive gear 500G is fixed to a drive shaft 500S coupled to a motor (not shown) as a drive source provided on the apparatus main body side, and a pair of switching gears is connected to the drive gear 500G. The gears 501G and 502G are always engaged.
[0050]
The switching gears 501G and 502G are pivotally supported by a switching plate 600 that is swingably provided on the drive shaft 500S. When the switching plate 600 swings about the drive shaft 500S, the switching gears 501G and 502G When either one engages with the gear 103G or the gear 203G, the developing roller 101 or 201 rotates. In FIG. 2, the switching gear 501G meshes with the gear 103G, and therefore the developing roller 101 rotates in the direction of the arrow.
[0051]
A part of the switching plate 600 is formed with a worm gear 800 that meshes with a worm 700 provided on the shaft of the motor 900, and the switching plate 600 is swung when the worm 700 is rotated forward and backward by the motor 900. .
[0052]
In FIG. 1, the second image forming unit II has the same configuration as that of the first image forming unit I, and includes a photosensitive drum 26, a charger 27, a writing unit 28, a B color developing device 300, and a D color. A developing device 400 and a cleaning unit 31 are provided, and are attached to the apparatus main body in the same posture as the first image forming unit I.
[0053]
The B color developing device 300 has the same configuration and functions as the developing roller 101, paddle roller 102, screw conveyor 103, and developer supply port 104 of the A color developing device 100. The developing roller 301, the paddle roller 302, the screw conveyor 303, the developing An agent supply port 304 is provided. Similarly, the D color developing device 400 also includes a developing roller 401, a paddle roller 402, a screw conveyor 403, and a developer supply port 404. The second image forming unit II also has the same mechanism as the rotation transmission mechanism shown in FIG. 2 that is applied to the first image forming unit I.
[0054]
Each of the image forming units I and II is detachably attached to the apparatus main body. The rotation of each of the photoconductive drums 16 and 26 is synchronized with the travel of the intermediate transfer belt 10, and the peripheral speed is determined so as to exactly match the travel speed of the intermediate transfer belt 10.
[0055]
Instead of the chargers 17 and 27, a charging means including a corona discharger or a brush can be employed. The A color developing device 100 of the first image forming unit I contains magenta toner, and the C color developing device 200 contains cyan toner. The B color developer 300 provided in the second image forming unit II, that is, the image forming unit closer to the transfer unit 45 accommodates yellow toner, and the D color developer 400 accommodates black toner.
[0056]
Since the black toner is used not only for color copying but also for black and white copying, in order to increase the copying speed when making black and white copying, the D color developing device 400 is connected to the second image forming unit II closer to the transfer unit 45. It is advantageous to provide it.
[0057]
The electrostatic latent images on the photosensitive drums 16 and 26 formed by a well-known method (uniform charging and writing) using the chargers 17 and 27 and the writing units 18 and 28 are respectively developed rollers 101, 201, Development is performed by 301 and 401. The four developing devices 100, 200, 300, and 400 have the same configuration, and a well-known color developing device can be adopted.
[0058]
Each of the photosensitive drums 16 and 26 is provided with a first transfer roller 41 and a second transfer roller 42 to which a transfer bias voltage is applied so as to be able to contact and separate from each other with the intermediate transfer belt 10 therebetween. The drive roller 13 is provided with a transfer roller 11 to which a transfer bias voltage is applied so as to be freely contacted and separated via the intermediate transfer belt 10.
[0059]
The photosensitive drums 16 and 26 are flat and slightly separated downward from the intermediate transfer belt 10, and the first transfer roller 41 and the second transfer roller 42 are separated upward from the intermediate transfer belt 10. In the step of transferring the toner images on the photosensitive drums 16 and 26 to the intermediate transfer belt 10, the intermediate transfer belt 10 is moved to the photosensitive drum 16 and / or the second transfer roller 42 by the first transfer roller 41 and / or the second transfer roller 42. Or it is made to contact 26.
[0060]
The drive roller 13 and the transfer roller 11 constitute a color image transfer unit 45. Instead of the first transfer roller 41 and the second transfer roller 42 as the transfer means, a corona discharger or a brush charger can be employed. The driven roller 12 is provided with a cleaning device 61 that removes toner remaining on the surface of the intermediate transfer belt 10 through the intermediate transfer belt 10.
[0061]
Below the first and second image forming units I and II, a sheet feeding device (not shown) for feeding the stacked transfer sheets one by one to the right in FIG. The sheet is fed to the transfer unit 45 by the single transfer sheet P, the feed roller pair 43, and the registration roller 44 fed from the sheet feeding device.
[0062]
Disposed above the transfer unit 45 is a fixing device 50 including a heating roller 47 that is rotationally driven in the direction of arrow b and a pressure roller 48 that rotates in pressure contact therewith. A roller 51 that applies an anti-offset liquid to the surface of the heating roller 47 is in contact with the heating roller 47 as necessary.
[0063]
On the downstream side of the fixing device 50, a pair of paper discharge rollers 54 for sending the transfer paper sent from the fixing device 50 onto the paper discharge tray 53 is disposed. An exhaust heat exhaust fan 55 is provided in the upper left part of FIG. 1, and prevents electrical components housed below the paper discharge tray 53 from being heated by the heat of the fixing device 50. .
[0064]
The operation of the configuration described above will be described.
(1) An electrostatic latent image corresponding to the A-color developing device 100 is formed on the photosensitive drum 16 of the first image forming unit I by the charger 17 and the writing means 18, and this electrostatic latent image is A-color developed. The image is visualized by the device 100 to obtain a magenta toner image (hereinafter referred to as “M image”). The M image is transferred to the intermediate transfer belt 10 by the first transfer roller 41.
[0065]
(2) On the other hand, as the intermediate transfer belt 10 travels in the direction of the arrow a, while the M image approaches the second image forming unit II, the photosensitive drum 26 is charged with the charger 27 and the writing unit 28 to develop the B color. An electrostatic latent image corresponding to the device 300 is formed, and the electrostatic latent image is visualized by the B color developing device 300 to obtain a yellow toner image (hereinafter referred to as a Y image). This Y image is transferred onto the intermediate transfer belt 10 by the second transfer roller 42 so as to overlap with the M image obtained by the first image forming unit 14.
[0066]
(3) While the superimposed image of the M and Y images approaches the first image forming unit I as the intermediate transfer belt 10 travels, the C color developing device is connected to the photosensitive drum 16 by the charger 17 and the writing unit 18. An electrostatic latent image corresponding to 200 is formed, and the electrostatic latent image is visualized by the C developing device 200 to obtain a cyan toner image (hereinafter referred to as C image). The C image is transferred onto the intermediate transfer belt 10 by the first transfer roller 41 so as to overlap the M and Y images.
[0067]
(4) While the superimposed image of the M, Y, and C images approaches the second image forming unit II as the intermediate transfer belt 10 travels, the D color is applied to the photosensitive drum 26 by the charger 27 and the writing unit 28. An electrostatic latent image corresponding to the developing device 400 is formed, and the electrostatic latent image is visualized by the D color developing device 400 to obtain a black toner image (hereinafter referred to as a BK image). This BK image is transferred onto the intermediate transfer belt 10 by the second transfer roller 42 so as to overlap the M, Y, and C images.
[0068]
When a color image is finally formed on the intermediate transfer belt 10, the transfer paper sent from the paper feeding device is sent to the transfer unit 45 by the registration roller pair 44, and the color image is transferred to the transfer paper here. The The color image transferred to the transfer paper is fixed to the transfer paper by the fixing device 50, and this transfer paper is sent out to the paper discharge tray 53 by the paper discharge roller 54. After the transfer of the color image, the residual toner is removed by the cleaning device 61 from the intermediate transfer belt 10.
[0069]
When obtaining a plurality of prints, when the superimposed image of the M and Y images is transferred to the intermediate transfer belt 10 by the second image forming unit II, the M image is subsequently intermediated by the first image forming unit I. The image is transferred onto the transfer belt 10 and the above steps (1) to (4) are repeated.
[0070]
When one of the two developing rollers 101 and 201 (or 301 and 401) in the image forming unit is rotating and working in order to develop the electrostatic latent image on the photosensitive drum in the above configuration and operation. The other one developing roller is stopped. As the developing roller, a well-known developing roller including a nonmagnetic sleeve that rotates during a developing operation and a magnet disposed in the nonmagnetic sleeve is employed.
[0071]
Further, when one developing roller is rotating and working to develop the electrostatic latent image on the photosensitive drum, the developer on the other developing roller moves to the photosensitive drum, and the photosensitive member In order to prevent color mixing due to the upper developer moving onto one of the other developing rollers, at least the developer on the non-operating developing roller whose rotation is stopped is brought into a non-contact state with respect to the photosensitive drum. There is a need.
[0072]
  [1] First embodiment:
  Here, as a means for bringing the developer on the non-operating developing roller into a non-contact state with respect to the photosensitive drum, the magnet in the developing roller is rotated to shift the position of the magnetic pole with respect to the photosensitive drum and formed on the developing roller This method employs a method of moving the developer ears to the non-contact position of the photosensitive drum.
[0073]
In FIG. 3, the developing roller 101 arranged on the upstream side in the rotation direction of the photosensitive drum 16 has a magnetic pole P1 out of the magnetic pole P1, the magnetic pole P2, the magnetic pole P3, the magnetic pole P4, and the magnetic pole P5 of the magnet 101a arranged inside. By rotating the non-magnetic sleeve 101b at an angle facing the photosensitive drum 16, the developer 1000 is brought into contact with the latent image on the photosensitive drum, and a developing bias voltage is applied to the non-magnetic sleeve 101b. Develop.
[0074]
At this time, in the developing roller 201 arranged on the downstream side of the photosensitive drum, the magnetic pole P1, the magnetic pole P2, the magnetic pole P3, the magnetic pole P4, and the magnetic pole P5 of the magnet 201a arranged inside are adjacent to the magnetic pole P1 and the magnetic pole P1. The distance between the magnetic pole P5 and the magnetic pole P5 is at an angle facing the photosensitive drum 16, the nonmagnetic sleeve 201b stops rotating, and the developer 1000 is not in contact with the photosensitive drum 16.
[0075]
Here, in the contact development method, in order to improve the image quality, it is necessary to ensure a sufficient contact state between the developer 1000 and the photosensitive drum 16, so that the interval between the photosensitive drum 16 and the nonmagnetic sleeve 201 b (development). The narrower the gap Gp), the more advantageous.
[0076]
On the other hand, in order to bring the developer 1000 and the photosensitive drum 16 into a non-contact state by rotating the internal magnet, the development gap Gp is developed at least on the nonmagnetic sleeve 201b between the magnet poles. It is necessary to make it larger than the agent thickness t1. Considering the above, it is desirable to set the development gap Gp to about Gp = t1 + 0.2 mm.
[0077]
By the way, in the so-called electrophotographic image forming apparatus in which the latent image formed on the photosensitive member as described above is visualized by a developer, a visible image is formed on the photosensitive member. There is a known problem that so-called scumming toner other than the necessary toner adheres. Some of the scumming toners have a small adhesion force to the photosensitive member, and such scumming toners on the developing roller in the non-development state when the development gap Gp is set as described above. It easily reattaches to the developer and enters the developing device, resulting in color mixing. In order to prevent this, when the development gap Gp is set larger, it is difficult to ensure a sufficient contact state of the developer with respect to the photosensitive drum, and it becomes difficult to improve the image quality.
[0078]
Therefore, a voltage is applied to the non-magnetic sleeve 201b of the developing roller 201 in the non-development state to generate an electrostatic force that presses the photosensitive drum 16 against the toner that is to adhere to the developer on the non-magnetic sleeve 201b. Then, a method for preventing the occurrence of color mixing was devised and the following experiment was conducted to confirm the effect.
[0079]
Developer: Two-component developer (magnetic carrier + nonmagnetic negatively charged toner)
Development gap Gp: 0.6mm
Developer thickness between magnet poles t1: 0.4 mm
Photoconductor charging potential V0 (non-image portion potential of latent image): -650V
Photoreceptor exposed portion potential VD (latent image portion): -100V
Development DC bias VB: -500V
Development AC bias: 1 kVpp (2 kHz)
Non-development state Development roller applied voltage V1: + 250V, 0V, -250V, -500V, -600V
As a result of the experiment, the effect of reducing the toner adhesion from the photosensitive drum to the non-development state developing roller at V1 = −250V, −500V, and −600V was confirmed, and in the case of using negatively charged toner (VB <VD), V1 <Mixed color reduction can be realized under conditions that satisfy VD.
Here, when positively charged toner is used (VB> VD), it is easily estimated that color mixing can be reduced under the condition of V1> VD.
[0080]
  UpAs a result of the experiment, the lower the potential of V1, the greater the effect of reducing the toner adhesion from the photosensitive drum to the non-development state developing roller, and no toner adhesion was confirmed at V1 = −600V. Therefore, when negatively charged toner is used (VB <VD), it is possible to reliably prevent color mixing under conditions that satisfy V1 <VB. Here, when positively charged toner is used (VB> VD), it is easily estimated that color mixing can be reduced under the condition of V1> VB.
[0081]
  negativeIn an electrophotographic image forming apparatus using charged toner (VB <VD), it is necessary to satisfy VB> V0. This is to prevent the negatively charged toner of the developer on the developing roller from adhering to the non-image portion (photosensitive member charged potential portion) during the developing operation of the latent image. This also applies to the non-development state developing roller applied voltage V1. That is, it is desirable to satisfy V1> V0 in order to prevent the negatively charged toner of the developer on the developing roller on the non-development state from adhering to the non-image area (photoconductor charging potential area) and degrading the image quality. Here, in the case of using positively charged toner (VB> VD), it is easily estimated that image quality deterioration can be prevented under the condition of satisfying V1 <V0.
[0082]
  Less thanIn the above embodiment, an image forming apparatus in which two developing devices are arranged with respect to an image bearing member which is a photosensitive drum has been described. The present invention is also applicable to an image forming apparatus in which three or more developing devices are arranged, such as an image forming apparatus in which four developing devices are arranged around an image carrier as described in JP-A-5-333701. The invention is effective.
[0083]
[2] Second embodiment
This will be described with reference to FIG. Here, as in FIG. 3, as a means for bringing the developer 1000 on the non-operating developing roller into a non-contact state with respect to the photosensitive drum 6 as the image carrier, the photosensitive drum is rotated by rotating a magnet in the developing roller. The method employs a method of shifting the position of the magnetic pole with respect to the position of the developer and moving the developer spike formed on the developing roller to the non-contact position of the photosensitive drum.
[0084]
In FIG. 4, an A color developing device 100 ′, a C color developing device 200 ′, a B color developing device 300 ′, and a D color developing device 400 ′ are arranged around the photosensitive drum 6. The developing roller 101 ′ of the A-color developing device 100 ′ disposed on the upstream side in the rotation direction of the photosensitive drum 6 is provided with a magnetic pole P1 ′, a magnetic pole P2 ′, a magnetic pole P3 ′, and a magnetic pole P4 ′ of the magnet 101a ′ disposed therein. , Of the magnetic pole P5 ′, the nonmagnetic sleeve 101b ′ is rotated at an angle at which the magnetic pole P1 ′ faces the photosensitive drum 6 to bring the developer 1000 into contact with the latent image on the photosensitive drum 6, and the nonmagnetic sleeve. Development is performed by applying a development bias voltage to 101b ′.
[0085]
At this time, the developing roller 201 ′ of the C color developing device 200 ′ disposed on the downstream side of the A color developing device 100 ′ and the downstream side of the C color developing device 200 ′ in the rotation direction of the photosensitive drum 6. The developing roller 301 ′ of the arranged B color developing device 300 ′ and the developing roller 401 ′ of the D color developing device 400 ′ arranged downstream of the B color developing device 300 ′ are magnets 201a arranged inside. ', 301a' and 401a 'have a magnetic pole P1', a magnetic pole P2 ', a magnetic pole P3', a magnetic pole P4 'and a magnetic pole P5', respectively, and the gap between the magnetic pole P1 'and the adjacent magnetic pole P5' is the photosensitive drum. The non-magnetic sleeves 201 b ′, 301 b ′, 401 b ′ are stopped from rotating at an angle facing 6, and the developer 1000 is not in contact with the photosensitive drum 6.
[0086]
As in the first embodiment, in order to improve the image quality, a sufficient contact state between the developer and the photosensitive drum is ensured, and the developer and the photosensitive drum are securely non-rotated by rotating the internal magnet. When the thickness of the developer 1000 is t1 in order to make the contact state, when the development gap Gp is set to about Gp = t1 + 0.2 mm, the photosensitive member is placed on the developer 1000 on the developing roller in the non-development state. In order to prevent red toner from adhering again, a voltage is applied to the non-magnetic sleeves 201b ′, 301b ′, 401b ′ of the developing rollers 201 ′, 301 ′, 401 ′ in the non-developing state, thereby By generating an electrostatic force that presses against the photosensitive drum 6 against the toner that is to adhere to the developer 1000 on the sleeves 201b ′, 301b ′, and 401b ′, it is possible to prevent the occurrence of mixed corrosion. The ability.
[0087]
When negatively charged toner is used (VB <VD), color mixing can be reduced under the condition of satisfying V1 <VD, but the photosensitive drum ground stain toner generated by the development of the A color developing device 100 ' , The potential changes sequentially under the influence of the applied voltage V1 of the non-magnetic sleeves 201b ′, 301b ′, 401b ′ of the C color developer 200 ′, B color developer 300 ′, and D color developer 400 ′. Thus, when the applied voltages V1 of the non-magnetic sleeves 201b ′, 301b ′, 401b ′ of the C-color developing device 200 ′, the B-color developing device 300 ′, and the D-color developing device 400 ′ are the same, the non-magnetic sleeve 201b ′. There is a possibility that the toner adhesion reduction effect in the non-magnetic sleeves 301b ′ and 401b ′ may be sequentially reduced as compared with the toner adhesion reduction effect in FIG.
[0088]
In this case, the applied voltages V1 ′, V1 ″, V1 ′ ″ of the nonmagnetic sleeves 201b ′, 301b ′, 401b ′ are set to V1 ′> V1 ″> V1 ′ ″, so that the toner adhesion reduction effect can be reduced. Decline can be prevented. Here, in the case of using positively charged toner (VB> VD), it is possible to prevent the toner adhesion reduction effect from being lowered by setting V1 ′ <V1 ″ <V1 ′ ″.
[0089]
  [3] Third embodiment:
  In FIG. 5, as in FIG. 3, as a means for bringing the developer 1000 on the non-operating developing roller into a non-contact state with respect to the photosensitive drum 16, the magnets 101a and 201a in the developing rollers 101 and 201 are rotated to be photosensitive. A method is adopted in which the position of the magnetic pole with respect to the body drum 16 is shifted and the spikes of the developer formed on the developing rollers 101 and 201 are moved to a position where they are not in contact with the photosensitive drum.
[0090]
In FIG. 5, the developing roller 201 arranged on the downstream side in the rotation direction of the photosensitive drum 16 indicated by an arrow is a magnetic pole among the magnetic pole P1, magnetic pole P2, magnetic pole P3, magnetic pole P4, and magnetic pole P5 of the magnet 201a arranged inside. The nonmagnetic sleeve 201b is rotated at an angle at which P1 opposes the photosensitive drum 16, the developer 1000 is brought into contact with the latent image on the photosensitive drum 16, and a developing bias voltage is applied to the nonmagnetic sleeve 201b. Development is performed.
[0091]
At this time, in the developing roller 101 arranged upstream in the rotation direction of the photosensitive drum 16, the magnet 101a is adjacent to the magnetic pole P1 among the magnetic pole P1, the magnetic pole P2, the magnetic pole P3, the magnetic pole P4, and the magnetic pole P5 arranged inside. The gap between the magnetic poles P <b> 5 is at an angle facing the photosensitive drum 16, the nonmagnetic sleeve 101 b stops rotating, and the developer 1000 is not in contact with the photosensitive drum 16.
[0092]
Here, as in the first embodiment, in order to improve the image quality, sufficient contact between the developer and the photosensitive drum is ensured, and the developer and the photosensitive drum are rotated by rotating the internal magnet. In order to ensure a non-contact state, assuming that the developer thickness between the magnetic poles is t, the development gap Gp is set to about Gp = t1 + 0.2 mm.
By the way, in the so-called electrophotographic image forming apparatus that visualizes the latent image formed on the photosensitive member with a developer as described above, the latent image formed on the photosensitive member has an exposed portion. A so-called edge effect is known in which the electric field is emphasized at the boundary between the non-exposed portion and the non-exposed portion. When the developing gap Gp is set as described above, the charged toner on the non-operating developing roller tends to adhere to the edge portion of the latent image on the photosensitive drum, and color mixing occurs in the image on the photosensitive drum 16. appear.
[0093]
In order to prevent this, when the development gap Gp is set larger, a sufficient contact state of the developer with the photosensitive drum cannot be ensured, and it becomes difficult to improve the image quality. Therefore, a voltage is applied to the non-magnetic sleeve 101b of the developing roller 101 in the non-development state, and an electrostatic force that attracts the toner on the non-magnetic sleeve 101b to the non-magnetic sleeve 101b is generated, thereby preventing color mixing. The method was devised and the following experiment was conducted to confirm the effect.
[0094]
Developer: Two-component developer (magnetic carrier + nonmagnetic negatively charged toner)
Development gap Gp: 0.6mm
Developer thickness between magnet poles t1: 0.4 mm
Photoconductor charging potential V0 (non-image portion potential of latent image): -650V
Photoreceptor exposure part potential VD (image part of latent image): -100V
Development DC bias VB: -500V
Development AC bias: 1 kVpp (2 kHz)
Non-development state Development roller applied voltage V2: + 250V, 0V
As a result of the experiment, the effect of preventing toner adhesion from the non-development state developing roller to the photosensitive drum was confirmed at V2 = + 250 V. When negatively charged toner is used (VB <VD), V2> VD is satisfied. Prevents color mixing. Here, when positively charged toner is used (VB> VD), it is easily estimated that color mixing prevention can be realized under the condition of V2 <VD.
[0095]
Another example will be described.
As a result of the above experiment, the higher the voltage V2, the greater the effect of preventing the toner from adhering to the photosensitive drum from the non-development state developing roller. However, increasing V2 to a certain degree affects the potential of the latent image on the photosensitive drum. There is a concern that the image quality will deteriorate. Since a sufficient toner adhesion preventing effect has been confirmed at V2 = + 250 V, development in the non-development state with respect to the potential difference VD−VB (+400 V in this experiment) between the photosensitive member exposure portion potential VD and the development DC bias VB If the potential difference V2−VD (+ 350V in this experiment) between the roller applied voltage V2 and the photosensitive member exposure part potential VD is small (V2−VD <VD−VB), the influence on the potential of the latent image on the photosensitive drum is affected. Thus, a sufficient toner adhesion preventing effect can be obtained without degrading the image quality.
Here, in the case of using positively charged toner (VB> VD), it is easily estimated that the color mixture reduction can be realized under the condition of V2-VD> VD-VB.
[0096]
In the third embodiment, the image forming apparatus in which the two developing devices are arranged with respect to the image bearing member which is the photosensitive drum has been described. However, the inventions according to claims 6, 7 and 8 are related arts. An image forming apparatus in which three or more developing devices are arranged, such as an image forming apparatus in which four developing devices are arranged around the image carrier described in JP-A-5-216337 and JP-A-5-333701. Needless to say, it is also effective against the above.
[0097]
Another example will be described.
In the above embodiment, as a means for bringing the developer on the non-operating developing roller into a non-contact state with the photosensitive drum, the magnet in the developing roller is rotated to shift the position of the magnetic pole with respect to the photosensitive drum. Although the method of moving the formed developer ears to the photosensitive drum non-contact position is adopted, the present invention is effective even if other methods are adopted.
[0098]
As a means for bringing the developer on the non-operating developing roller into contact with the photosensitive drum, the non-operating developing roller is moved away from the peripheral surface of the photosensitive drum so that the developer on the roller does not contact the photosensitive drum. When the developing device contact / separation method is adopted, by applying the present invention, the contact / separation movement distance of the developing device can be significantly shortened compared to the conventional developing device contact / separation method, and the contact is possible. The means, the contact / separation driving means, and the contact / separation space can be greatly simplified, reduced in size, and reduced in cost.
[0099]
Further, the developing roller reverse rotation system disclosed in JP-A-5-216337 and JP-A-5-333701, and the developer introduction / shut-off switching system disclosed in JP-A-5-216337 and JP-A-11-338257 are used. In this case, by applying the present invention, it is not necessary to rotate the developing roller until the developer on the developing roller is completely removed, and it is sufficient that the developer is not in contact with the image carrier. For this reason, the time during which a visible image cannot be formed on the image carrier can be greatly shortened, and the speed can be increased.
[0100]
[4] Fourth embodiment
In the above embodiment, the non-operating developing roller adopts a contact developing method in which the developer is brought into a non-contact state with respect to the photosensitive drum, and the developing roller in the operating state is brought into contact with the developer and the image carrier. The present invention is effective even if a non-contact development method in which development is performed in a state where the developer and the image carrier are not in contact with each other is employed.
[0101]
This will be described with reference to FIGS.
Here, a non-contact development method is employed in which the developer on the developing roller is developed in a non-contact state with respect to the photosensitive drum.
[0102]
Example 1.
In FIG. 6, the developing roller 101 arranged on the upstream side in the rotational direction indicated by the arrow with respect to the photosensitive drum 16 is a magnetic pole among the magnetic pole P1, magnetic pole P2, magnetic pole P3, magnetic pole P4, and magnetic pole P5 of the magnet 101a arranged inside. The nonmagnetic sleeve 101b is rotated at an angle between the pole P1 and the magnetic pole P5 so as to face the photosensitive drum 16, thereby bringing the developer 1000 into a non-contact state with respect to the latent image on the photosensitive drum 16, and the nonmagnetic sleeve 101b. On the other hand, development is performed by applying a development bias voltage.
[0103]
At this time, in the developing roller 201 disposed downstream of the developing roller 101 in the rotation direction of the photosensitive drum 16, the magnet 201a disposed inside includes a magnetic pole P1, a magnetic pole P2, a magnetic pole P3, a magnetic pole P4, and a magnetic pole. Among P5, the nonmagnetic sleeve 201b stops rotating at an angle between the magnetic pole P1 and the adjacent magnetic pole P5 facing the photosensitive drum 16, and the developer is not in contact with the photosensitive drum. ing.
[0104]
In FIG. 7, the developing roller 201 arranged on the downstream side in the rotation direction indicated by the arrow with respect to the photosensitive drum 16 is an angle at which the pole between the magnetic pole P <b> 1 and the magnetic pole P <b> 5 of the magnet 201 a arranged inside faces the photosensitive drum 16. Then, the nonmagnetic sleeve 201b is rotated to bring the developer 1000 into a non-contact state with respect to the latent image on the photosensitive drum 16, and development is performed by applying a developing bias voltage to the nonmagnetic sleeve 201b.
[0105]
At this time, in the developing roller 101 disposed on the upstream side of the developing roller 101 in the rotation direction of the photosensitive drum 16, the magnet 101a disposed inside has a distance between the magnetic pole P1 and the adjacent magnetic pole P5 between the photosensitive rollers. The nonmagnetic sleeve 101b stops rotating at an angle facing the drum 16, and the developer is not in contact with the photosensitive drum.
[0106]
Here, in the non-contact development method, in order to improve the image quality, it is more advantageous that the distance between the photosensitive drum and the nonmagnetic sleeve (development gap Gp) is narrower. On the other hand, in order to bring the developer and the photosensitive drum into a non-contact state, it is necessary to make the development gap at least larger than the developer thickness t1 on the nonmagnetic sleeve between the magnet poles. Considering the above, it is desirable to set the development gap Gp to about Gp = t1 + 0.2 mm.
[0107]
Here, in FIG. 6, as described above, the scumming toner on the photosensitive drum 16 reattaches to, for example, the developer on the developing roller 201 in a non-development state, and enters the developing device. There is concern about the problem of color mixing.
[0108]
Therefore, a voltage is applied to the non-magnetic sleeve 201b of the developing roller 201 in the non-development state to generate an electrostatic force that presses the photosensitive drum 16 against the toner that is to adhere to the developer on the non-magnetic sleeve 201b. Thus, color mixing can be prevented.
[0109]
Further, in FIG. 7, the charged toner on the developing roller 101 in the non-operating state adheres to the edge portion of the latent image on the photosensitive drum, and there is a concern that color mixing may occur in the image on the photosensitive drum. Therefore, a voltage is applied to the non-magnetic sleeve 101b of the developing roller 101 in the non-development state, and an electrostatic force that attracts the toner on the non-magnetic sleeve 101b to the non-magnetic sleeve 101b is generated, thereby preventing color mixing. it can.
[0110]
Here, in this embodiment, as compared with the first, second, and third embodiments, it is not necessary to provide means for bringing the developer on the non-operation developing roller into a non-contact state with respect to the photosensitive drum. In addition, the apparatus can be simplified, downsized, and the cost can be reduced, and the speed of the apparatus can be increased because it is not necessary to perform the operation of bringing the developer on the non-operation developing roller into a non-contact state with respect to the photosensitive drum.
[0111]
Example 2.
In the first, third, and fourth embodiments described above, a plurality of image forming units in which a latent image forming unit and a plurality of developing units are arranged around the image carrier shown in FIGS. The embodiment in which the present invention is applied to the image forming apparatus that obtains a multi-color image by sequentially transferring the visible image formed in step 1 onto a single intermediate transfer member has been described.
[0112]
In this type of image forming apparatus, a visible image is formed on an image carrier by a plurality of developing means presented in JP-A-5-142918, JP-A-6-324571, and JP-A-2000-172043. It is possible to obtain a high-quality image as compared with a method of obtaining a multi-color image by forming multiple layers. Further, a visible image formed on a single image carrier by a plurality of developing means presented in JP-A-5-216337, JP-A-5-333701, and JP-A-11-338257, The apparatus can be reduced in size, reduced in cost, and increased in speed as compared with the method in which the images are sequentially overlaid and transferred onto the intermediate transfer member and a multi-color image is formed on the intermediate transfer member.
[0113]
For this reason, by applying the present invention to this type of image forming apparatus, the effects of the present invention can be synergistically obtained with respect to higher image quality, smaller size, lower cost, and higher speed. It becomes possible.
[0114]
【The invention's effect】
  In the present invention, the developing gap can be narrowed for each of the plurality of developing devices, and high image quality can be realized. Since the color mixing in the developing device can be reliably reduced, it is possible to reliably suppress the output image quality deterioration.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of an image forming apparatus using an intermediate transfer belt.
2 is a means for switching the development state and non-development state of the development device for the image forming apparatus of FIG.
FIG. 3 is a partial front view illustrating the arrangement of a photosensitive drum and a developing roller.
FIG. 4 is a partial front view illustrating the arrangement of a photosensitive drum and a developing roller.
FIG. 5 is a partial front view illustrating the arrangement of a photosensitive drum and a developing roller.
FIG. 6 is a partial front view illustrating the arrangement of the photosensitive drum and the developing roller.
FIG. 7 is a partial front view illustrating the arrangement of the photosensitive drum and the developing roller.
[Explanation of symbols]
6, 16 Photosensitive drum
101, 201, 301, 401, 101 ', 201', 301 ', 401' Developing roller

Claims (1)

A plurality of developing devices for developing the latent image on the image carrier configured to be rotatable are arranged around the image carrier along the rotation direction of the image carrier, and one development in the plurality of developing devices is provided. When the apparatus is in the developing state, the other developing apparatuses are controlled to be in the non-developing state, and the image forming apparatus that performs multicolor development by sequentially changing the developing apparatus in the developing state to another developing apparatus The visible image developed by the developing device in the developing state passes through the developing device in the non-developing state disposed downstream of the developing device in the developing state in the rotation direction of the image carrier. The potential V1 of the developing device disposed on the downstream side in the rotation direction satisfies the following condition (1), and a plurality of non-developing developing devices are further provided downstream of the developing device in the developing state. If so, the current While the visible image developed in the developing device in the state passes, the potential V1 ′ of any developing device among the plurality of downstream developing devices, the developing device disposed downstream of the developing device An image forming apparatus characterized in that the potential V1 ″ satisfies the following condition (2) .
(1) When VB <VD, V1 <VD , and when VB> VD, V1> VD . (2) When VB <VD, V1 ′> V1 ″, and when VB> VD, V1 ′ <V1 ″. However, VB is the potential of the developing device in the developing state, and is only the DC component when an alternating electric field is applied . VD is the potential of the image portion of the latent image (the portion where the toner adheres) .

Images