JP2005010562A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form good images over a long period of time by preventing the nonuniformity of toner coating due to the stagnation of the foreign substances recovered into a developing device. <P>SOLUTION: The image forming apparatus of a cleanerless plus twin sleeve system recovers the foreign substances, such as paper dust, stagnated in the gaps of a first developing roller and a second developing roller into the developing device by changing the peripheral speed ratio of the two developing rollers while paper is not passed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to an image forming apparatus such as a copying machine or a printer, and more particularly to an image forming apparatus that transfers a developer image formed and supported on an image carrier onto a transfer material. More specifically, the electrostatic latent image formed on the image carrier is developed using two developing rollers, and at the same time, the image forming apparatus that collects the developer remaining on the image carrier after transfer and the attached foreign matter is recovered. About.
[0002]
[Prior art]
Conventionally, in such an image forming apparatus, after the latent image carrier is uniformly charged, analog exposure or image exposure with a semiconductor laser or LED is performed to form an electrostatic latent image on the latent image carrier. After the formation, the electrostatic latent image is visualized as a developer image by a developing device, the developer image is transferred to a transfer material as a recording medium, and then the transfer material is separated from the latent image carrier and a fixing device. There is known an image forming apparatus that outputs a fixed image by performing a fixing process.
[0003]
First, the operation of the conventional image forming apparatus will be described with reference to FIG.
[0004]
The image forming apparatus includes a photosensitive drum 101 that is a latent image carrier that includes a photoconductive layer such as OPC or a-Si and rotates in the direction of arrow B.
[0005]
In such an image forming apparatus, first, the surface of the photosensitive drum 101 is uniformly charged to, for example, −700 V by the primary charger 102.
[0006]
Next, the image exposure 103 according to the image signal information attenuates the surface potential of the exposed portion on the photosensitive drum 101 to −200 V, for example, and forms a latent image on the photosensitive drum 101 according to the image signal of the image. For the image exposure 103, for example, a semiconductor laser or an LED array is used.
[0007]
Next, the latent image is developed and visualized as a toner image by the developing device 104 which is a developing device using a dry one-component developer. A developing device using a dry one-component developer is simple and does not require replacement of a carrier or the like and has a high durability and a long life. For example, there is a jumping development using a magnetic one-component toner. The developing device 104 uses negatively charged black toner. At the time of development, a DC bias of about −500 V is applied as a developing bias to the developing sleeve that is a developer carrying member provided in the developing device 104 to reversely develop the latent image on the photosensitive drum 101.
[0008]
Thereafter, a pre-transfer process is performed using a post charger 105 as necessary (usually, corona is applied by DC or AC, or light neutralization is combined), and the transfer material supplied to the photosensitive drum 101 is applied. The image is transferred by the transfer charger 106.
[0009]
Thereafter, the transfer material subjected to the transfer process is sent to a fixing device 107 as a fixing device, and the toner image is fixed on the transfer material to obtain an image. On the other hand, transfer residual toner that is not subjected to development and remains on the photosensitive drum 101 and foreign matter adhering to the photosensitive drum 101 are removed by the cleaning device 108 to prepare for the next image formation.
[0010]
On the other hand, in order to increase the speed of the image forming apparatus, the conventional developing apparatus is provided with a plurality of developing sleeves in a developing apparatus using a two-component magnetic brush as described in Japanese Patent Laid-Open No. 03-204084. Or a plurality of developing sleeves as developer carriers as described in JP-A-02-188778, and the distance between each developing sleeve and the photosensitive member as a latent image carrier There is known a developing device in which the toner supply amount from the developing sleeve to the photosensitive member is made uniform by bringing the developing sleeve closer to the downstream side in the rotation direction.
[0011]
Conventionally, in a developing device having a plurality of developing sleeves, as disclosed in Japanese Examined Patent Publication No. 3-5579, in order to reduce the size of the image forming apparatus, development with a reduced size of the developing sleeve is performed. The device is known.
[0012]
In the developing device having such a plurality of developing sleeves, it is excellent in terms of maintaining the image density, and a magnetic blade or the like is used for the toner layer thickness regulation for the developing sleeve disposed upstream in the rotation direction of the latent image carrier. In contrast, since the downstream developing sleeve uses the upstream developing sleeve to regulate the toner layer thickness, there is no need to provide a separate toner layer thickness regulating member between the plurality of developing sleeves, providing excellent compactness and saving space. It is.
[0013]
[Problems to be solved by the invention]
However, in order to reduce the size of the image forming apparatus and reuse the transfer residual toner, a developing apparatus that simultaneously performs development of an electrostatic latent image and recovery of transfer residual toner and foreign matter with a plurality of developing sleeves, except for a cleaning apparatus. Although the collected toner residual toner is collected in the developing machine together with the toner coated on the sleeve and reused according to the toner layer thickness regulation, the collected foreign matter stays between the adjacent developing sleeves. As a result, the toner layer thickness of the developing sleeve on the downstream side cannot be made uniform, or the developing sleeve itself is damaged and a good image cannot be obtained.
[0014]
In order to avoid such a phenomenon, there is a configuration in which a conductive brush or roller is brought into contact with the surface of the photosensitive member 101 to temporarily collect the transfer residual toner and foreign matters and to discharge only the toner. As a result, the cost of the device has increased significantly, and the device has become more complicated and larger, which has been an obstacle to saving space and reducing costs.
[0015]
(Object of the present invention)
Accordingly, the present invention has been made to address the above-described problems in an image forming apparatus that simultaneously collects development with a plurality of developing sleeves for the purpose of reusing transfer residual toner, and prevents the development of foreign matter and the development sleeve. The object is to make the upper toner coat uniform and provide a good image over a long period of time.
[0016]
[Means for Solving the Problems]
(1) a charging unit that charges the surface of the charged body on a rotatable body to be charged, an exposure unit that records image information on the surface of the charged body, a developing unit that visualizes the image information with a developer, In an image forming apparatus comprising: transfer means for transferring a developer image onto a transfer material; and recovery means for recovering toner remaining on the surface of the object to be charged without being transferred by the transfer process, and foreign matter adhering to the surface of the object to be charged The collecting means is an image forming process which is also used by the developing means, and the developing means has two rotatable developer carriers, and the developing means is located on the upstream side with respect to the rotation direction of the charged body. The developer carrying member has a layer thickness of the developer attached by the developer regulating member, and is forwardly rotated in the rotation direction of the charged body at a position closest to the charged body. Located downstream of the direction of rotation The developer carrying member has a layer thickness of the developer adhering to the developer carrying member upstream, and is forwardly rotated in the rotation direction of the charged member at a position closest to the charged member. An image forming apparatus, wherein a peripheral speed ratio between the upstream developer carrier and the downstream developer carrier is changed during non-image formation.
[0017]
(2) The image forming apparatus according to (1), wherein the rotation speed of the developer carrier on the downstream side is higher than the rotation speed of the developer carrier on the upstream side.
[0018]
(3) The image forming apparatus according to (1), wherein the rotation of the developer carrier on the upstream side is stopped.
[0019]
(4) In (1), (2), (3), the peripheral speed ratio between the upstream developer carrier and the downstream developer carrier is changed immediately before the exposure step. The image forming apparatus described.
[0020]
(5) The peripheral speed ratio between the upstream developer carrier and the downstream developer carrier is changed immediately after the exposure step. (1), (2), (3) Image forming apparatus.
[0021]
(Function)
By executing the above means, the following effects can be obtained.
[0022]
(1) Foreign matter can be collected in the developing device main body, the toner coat of the developing sleeve on the downstream side can be made uniform, and a good image can be obtained over a long period of time.
[0023]
(2) A low-cost and space-saving image forming apparatus can be provided.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
[0025]
(Example 1)
FIG. 1 shows a schematic configuration of the image forming apparatus of this embodiment.
[0026]
The process speed of the image forming apparatus of this embodiment is a black-and-white digital copying machine with a process speed of 460 mm / sec and 90 sheets per minute, and an a-Si drum photoconductor of φ108 is used as a photoconductor as a latent image carrier. The a-Si drum photoconductor is more durable and has a lifespan of 3 million sheets or more as compared with the OPC photoconductor, and is suitable for a high-speed machine.
[0027]
In such an image forming apparatus, as shown in FIG. 1, a photosensitive drum 1 as a latent image carrier is uniformly charged to, for example, +500 V by a charger 2, and then image exposure 3 is performed at 600 dpi. The image exposure 3 is a laser beam modulated by an image signal using a semiconductor laser as a light source. The laser beam is polarized by a polygon mirror rotating at a constant rotation speed by a motor, reflected by a folding mirror through an imaging lens. Thereafter, the photosensitive drum 1 is raster-scanned, and the surface potential of the exposed portion is attenuated to, for example, +100 V to form an electrostatic latent image. The wavelength of the outer laser beam is 680 mm.
[0028]
Thereafter, the electrostatic latent image is visualized as a toner image by the developing device 4 being developed with a bias in which a rectangular wave having a DC voltage of +300 V, Vpp of 1.5 kV, and a frequency of 2.6 kHz is superimposed.
[0029]
In this embodiment, development is performed using a black magnetic one-component developer, which is a simple and highly durable development method requiring no maintenance up to 1 million sheets of the development sleeve, and regular development using two development sleeves is performed. .
[0030]
FIG. 2 is a configuration diagram of the developing device 4 of this embodiment. The two developing sleeves 41 and 42 rotate at the speeds v1 and v2 in the directions of the arrows, respectively, and v1 = v2. Further, the two developing sleeves 41 and 42 are arranged in parallel with a gap of 300 μm with respect to the drum and with a gap of 400 μm between the developing sleeves. Further, the magnetic blade 43 is used to regulate the toner layer thickness of the upstream developing sleeve 41, whereas the downstream developing sleeve 42 has a toner layer thickness that depends on the toner conveying force, gap, and magnetic force with the developing sleeve 41. Regulate.
[0031]
Of the two developing sleeves, the upstream developing sleeve 41 develops the electrostatic latent image formed on the photosensitive drum 1 as in the prior art, and the downstream developing sleeve 42 collects the excessively developed toner. On the other hand, toner is supplied to a place where toner is scarce, and so-called toner image treatment is performed. As a result, the visible toner image becomes faithful to the electrostatic latent image, and a good image can be obtained.
[0032]
After the electrostatic latent image on the photosensitive drum 1 is converted into a toner image by the developing device 4, the toner image is charged with a total current of −200 μA (AC + DC) by the post charger 5 and then transferred in the direction of the arrow. The transfer material transferred by the transfer charger 6 and transferred with the toner image is sent to a fixing device 7 as a fixing device, and the toner image is fixed.
[0033]
Further, the toner remaining on the photosensitive drum 1 without being transferred to the transfer material, the toner transferred to the transfer drum after being transferred to the transfer drum (hereinafter referred to as transfer residual toner), or the transfer material. The foreign matter transferred onto the photosensitive drum 1 is positively charged by the charger 2 and then developed / collected by the developing device 4.
[0034]
Next, the development / collection performed in the developing device 4 of this embodiment will be described in detail with reference to FIG.
[0035]
The photosensitive drum 1 is uniformly charged by the charger 2 and the transfer residual toner and the foreign matter T ′ are given a positive charge. Thereafter, an electrostatic latent image is formed by the image exposure 3, so that transfer residual toner and foreign matter are present in the exposed portion and in the unexposed portion. When untransferred toner and foreign matter T ′ are present in the exposed portion 31 on the drum (FIG. 3A), the photosensitive drum 1 is exposed to the potential difference between the potential of the photosensitive drum 1 and the bias applied to the developing sleeves 41 and 42. Instead of being collected, a toner image is formed with newly developed toner and reused. In addition, when untransferred toner and foreign matter are present in the unexposed portion on the drum (FIG. 3-2), the photosensitive drum 1 has a potential difference between the potential of the photosensitive drum 1 and the bias applied to the developing sleeves 41 and 42. To the developing sleeves 41 and 42. This process is performed by the two developing sleeves 41 and 42, but most of the process is collected by the upstream developing sleeve 41.
[0036]
Next, the collected toner is transported into the developing device 44 by the toner transport force of the upstream developer carrier, or the downstream developer carrier by the toner transport force of the downstream developer carrier. Or used as an upper toner layer.
[0037]
However, if the collected foreign matter has a diameter equivalent to that of the toner (5 to 10 μm), the process proceeds in the same manner as the above-described toner, but other cases are located at the locations indicated by the dotted lines in FIG. In other words, it stays on the downstream side in the rotation direction of the developing sleeve 42 and in the vicinity of the developing sleeves 41 and 42. According to the studies by the authors and the like, since the rotation speeds V1 and V2 of the developing sleeves 41 and 42 are equal, the toner conveying forces N1 and N2 are balanced, and the large foreign matter loses the force necessary for conveying. It turns out that it is caused by being closed. If the amount of staying foreign matter is small, there is no problem, but after the endurance of 1 million sheets, the staying foreign matter obstructs the toner layer formation of the developing sleeve 42, and the top of the developing sleeve becomes a streak. It is had. Since the toner layer on the downstream developing sleeve, which played a role as a toner image treatment, is a streak, the toner image is destroyed instead of performing the treatment, and a good image cannot be obtained. There has occurred.
[0038]
Therefore, in this embodiment, the peripheral speed ratio between the developing sleeves 41 and 42 is changed so that the staying foreign matter is conveyed into the developing device 44. More specifically, by making the rotational speed V1 of the developing sleeve 41 faster than the rotational speed V2 of the developing sleeve 42 (V1> V2), the balance of the toner conveying force that has been balanced so far is broken (N1> N2), The foreign matter was made easy to be conveyed into the developing device 44.
[0039]
As a result, the foreign matter staying in the vicinity of the developing sleeves 41 and 42 is transported into the developing device 44 by the upstream toner transporting force N1, and as described above, streaks are generated in the toner layer on the downstream developing sleeve. There was nothing.
[0040]
(Example 2)
In the above embodiment, the foreign matter staying in the vicinity of the developing sleeves 41 and 42 can be prevented, but the foreign matter transported into the developing unit 44 together with the toner is transported to the magnetic blade 43 as it is. The toner layer stayed, and the toner layer of the developing sleeve 41 was not formed and became a streak. When the level was slight, a good image could be supplied due to the treatment effect of the developing sleeve 42, but at the end of the durability, the developing sleeve 42 could not be corrected and a good image could not be obtained. .
[0041]
Therefore, in this embodiment, the rotational speed V2 of the developing sleeve 42 is made faster than the rotational speed V1 of the developing sleeve 41 (V1 <V2), and the balance of the toner conveying force is lost (N1 <N2). As a result, the staying foreign matter is conveyed into the developing device 44 by the developing sleeve 42 together with the toner. According to the studies by the authors and the like, it has been found that the conveyed foreign matter is conveyed as it is by the developing sleeve and developed again, or dispersed by the stirring member 45 in the developing device 2.
[0042]
As a result, in the same manner as in Example 1, the stay of foreign matters was prevented, and no streaks were generated in the toner layer on the developing sleeves 41 and 42.
[0043]
In this embodiment, the rotation speed V2 of the developing sleeve 42 is increased, but the rotation speed V1 of the developing sleeve 41 is decreased, the rotation of the developing sleeve 41 is stopped, or the speed control of the developing sleeves 41 and 42 is simultaneously performed. However, the same effect can be obtained.
[0044]
Example 3
In the above embodiment, it is possible to prevent foreign matter from staying and to prevent the generation of streaks on the developing sleeve. However, if the balance of toner conveyance is lost, the toner layer of the developing sleeve 42 is not uniform, and half When a tone image was formed, the treatment effect in the developing sleeve 42 was impaired, and the image was uneven.
[0045]
Therefore, in this embodiment, the peripheral speed ratio of the developing sleeves 41 and 42 is changed during the rotation before the latent image formation (hereinafter referred to as the pre-rotation) so that the speed is constant during the image formation. More specifically, the foreign material staying in the previous image formation makes the rotational speed V2 of the developing sleeve 42 faster than the rotational speed V1 of the developing sleeve 41 during the previous rotation (V1 <V2), and the balance of the toner conveying force is lost (N1 < N2), the sheet is conveyed into the developing device 44, and during image formation, the rotation speed of the developing sleeves 41 and 42 is made constant (V1 = V2), and the toner layer of the developing sleeve 42 is controlled to be uniform. Thus, the staying foreign matter is conveyed into the developing device 44 by the developing sleeve on the downstream side together with the toner only at the time of the previous rotation, and a uniform toner layer is formed at the time of image formation. According to the study by the authors and the like, it is known that streaks do not occur on the developing sleeve 42 if the foreign matter stays for a short period or in a small amount. Further, since the balance of the toner conveying force is balanced during image formation, foreign matter stays in the vicinity of the developing sleeves 41 and 42 in the developing device 44, that is, upstream of the developing sleeve 42 in the rotation direction and in the vicinity of the developing sleeves 41 and 42. However, when the toner layer is formed on the developing sleeve 42, streaks or the like may not occur in a place where foreign matter has conventionally accumulated, that is, downstream of the developing sleeve 42 in the rotation direction and in the vicinity of the developing sleeves 41 and 42. I know it.
[0046]
As a result, it was possible to prevent foreign matter from staying as in the above embodiment, to uniformly form the toner layers of the developing sleeves 41 and 42, and to form a good image over a long period of time. Moreover, since measures could be taken without using a foreign material recovery member or separation member, low cost and space saving could be achieved.
[0047]
In this embodiment, the peripheral speed ratio of the developing sleeves 41 and 42 is changed during rotation before forming a latent image (hereinafter referred to as pre-rotation) so as to be constant during image formation. The peripheral speed ratio of the developing sleeves 41 and 42 is changed during the formation (hereinafter referred to as the paper interval) or during the rotation after the latent image is formed (hereinafter referred to as the post-rotation) so that the speed is constant during the image formation. However, the same effect can be obtained.
[0048]
【The invention's effect】
As described above, by changing the peripheral speed ratio of the upstream and downstream developer carriers and collecting the accumulated foreign matter in the developing device 2, it was possible to provide a good image over a long period of time. In addition, toner reuse could be achieved at low cost and space saving.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment.
FIG. 2 is a schematic configuration diagram of a developing device 4;
FIG. 3 is a schematic diagram of toner recovery when exposure is performed.
3-2 Schematic of toner recovery without exposure.
FIG. 4 is a schematic view between sleeves.
FIG. 5 is a conventional image forming apparatus.
[Explanation of symbols]
1/101 photosensitive drum 2/102 charger 3/103 image exposure 4/104 developing device 5/105 post charger 6/106 transfer charger 7/107 fixing device 31 electrostatic latent image 41 upstream developing sleeve 42 downstream Developing sleeve 43 Magnetic blade 44 Developer 45 Stirring member 108 Cleaning device N1 Toner conveying force N2 of upstream developing sleeve Toner conveying force T of downstream developing sleeve Toner T ′ Transfer residual toner and foreign matter V1 Rotating speed V2 of upstream developing sleeve Rotation speed of downstream development sleeve

Claims (5)

A charging means for charging the surface of the charged body on a rotatable charged body, an exposure means for recording image information on the surface of the charged body, a developing means for visualizing the image information with a developer, and a developer image In an image forming apparatus, the image forming apparatus includes: a transfer unit that transfers the toner to a transfer material; and a recovery unit that recovers the toner that is not transferred by the transfer process and remains on the surface of the charged body, and the foreign matter attached to the surface of the charged body
The recovery means is an image forming process that the developing means also serves as,
The developing means has two rotatable developer carriers.
The developer carrying member positioned on the upstream side with respect to the rotation direction of the member to be charged has its developer layer thickness regulated by a developer regulating member, and the developer carrying member at the closest position to the member to be charged. Forward rotation in the direction of rotation of the object to be charged,
The developer carrier positioned downstream with respect to the rotation direction of the member to be charged has its developer layer thickness regulated by the upstream developer carrier and is closest to the member to be charged. Forward rotation in the direction of rotation of the member to be charged at the position,
An image forming apparatus, wherein the peripheral speed ratio between the upstream developer carrier and the downstream developer carrier is changed during image formation and non-image formation. 2. The image forming apparatus according to claim 1, wherein the rotation speed of the developer carrier on the downstream side is higher than the rotation speed of the developer carrier on the upstream side. The image forming apparatus according to claim 1, wherein the rotation of the upstream developer carrier is stopped. 4. The image forming apparatus according to claim 1, wherein the peripheral speed ratio between the upstream developer carrier and the downstream developer carrier is changed immediately before the exposure step. 4. The image forming apparatus according to claim 1, wherein the peripheral speed ratio between the upstream developing roller and the downstream developing roller is changed immediately after the exposure step.

Images