JPH09311537A - Toner concentration control method and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the scattering of toner, soiling inside an image forming device, surface staining of a formed image, etc., caused by the increase of the concn. of the toner in the vicinity of the end part of a developer carrier by suppressing the increase of the concn. of the toner in the vicinity of the end part of the developer carrier, in the case a toner concentration self-control mechanism is provided. SOLUTION: When an image is not formed, a latent image being a black solid image is formed by development in the end part in a longitudinal direction of a photoreceptor drum 11 and turned into a visible image by a developing sleeve 4. Thus, the carriers of an adjacent part having a high bulk density are moved to a part where the bulk density of the toner is lowered because of the fact that the black solid image A is turned into the visible image to make the distribution of the toner concn. in the end part in the longitudinal direction on the developing sleeve 4 almost uniform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile, and a printer.
The present invention relates to an image forming apparatus including a latent image carrier that holds a latent image and a developing device that develops a latent image formed on the image carrier using a two-component developer composed of toner and magnetic particles. .

[0002]

2. Description of the Related Art Conventionally, a developing device for developing a latent image formed on an image carrier using a two-component developer (hereinafter referred to as a developer) composed of toner and magnetic particles has a complicated structure using a toner density sensor or the like. It has been proposed to control the toner concentration without providing a toner concentration self-control mechanism (for example, Japanese Patent Application Laid-Open No. 63-225266, Japanese Patent Application No. 7-11).
9339 publication).

For example, in Japanese Patent Laid-Open No. 63-225266, a developer regulation is arranged to face the surface of the developer carrier in the developer accommodating portion and regulate a developer layer carried on the surface of the developer carrier. A substantially immovable layer as a developer accommodating portion mainly containing the magnetic particles is formed from the member to the upstream side in the rotation direction of the developer carrier, and further upstream of the immovable layer in the rotation direction. It has been proposed to form a toner particle intake region into the developer carried by the developer carrier.

In this developing device, the size of the toner particle intake region is automatically increased or decreased by adding or detaching the magnetic particles to or from the immobile layer. Specifically, when the number of magnetic particles existing in the immovable layer becomes large, the size of the toner particle intake region decreases, and the amount of new toner taken into the developer that contributes to development decreases. On the other hand, when the amount of the magnetic particles existing in the immovable layer becomes small, the toner particle intake area increases and a large amount of toner is taken in. Thereby, the mixing ratio of the magnetic particles and the toner particles in the developer layer is automatically controlled. According to this type of developing device, long-term toner concentration control is automatically performed without providing a special mechanism for detecting the toner concentration in the developer and performing toner concentration self-control based on the detection result. Can be done on a regular basis.

Further, Japanese Patent Application No. 7-119339 discloses a developer regulating member for regulating the amount of the developer carried on a developer carrying member and conveyed to a toner particle intake region, and the developer regulating member. In order to form a developer retention portion in which the blocked developer is retained, a developer holding member is disposed to face the surface of the developer bearing member with a predetermined gap, and the development on the developer bearing member in the developer retention portion is performed. The toner accommodating portion which is adjacent to the developer carrying direction from the upstream side and has a toner replenishing opening facing the developer carrying member, and the toner taken into the developer retaining portion through the toner replenishing opening have an upper limit toner concentration. In this state, the developer layer formed above the interface formed in the developer retaining portion has a space capable of moving in the direction opposite to the conveying direction of the developer layer on the developer carrier. Equipment is proposed . According to this type of developing device,
The volume of the developer moving layer that rotates along with the rotation of the developer carrier changes according to the state of taking toner into the magnetic particles, and as the toner is taken in by the magnetic particles, the developer moving layer causes the toner replenishment opening portion to move. Since it expands so as to close it, the upper limit of the amount of toner taken in by the magnetic particles is determined,
The toner density does not exceed the upper limit density. Therefore, the toner concentration can be automatically controlled by presetting the amount of magnetic particles staying in the developer staying portion.

Further, Japanese Patent Application No. 7-119340 discloses an opening for communicating the inside between a developing device main body containing a developer carrying member and an opening / closing means capable of opening and closing the opening. It has been proposed that the developer accommodating portion is configured by a developer accommodating container that is provided and is detachable from the main body of the developing device. According to this configuration, by closing the opening by the opening / closing means provided in the opening of the developer container, the developer in the developer container in which most of the developer in the apparatus exists can be collected. Also, the developer can be easily replaced by detaching the developer container from the developer body.

[0007]

FIG. 7 shows a magnetic force distribution a in the longitudinal direction of the developer carrying member and a developer in a general developing device using a developer carrying member carrying a developer by magnetic force. The distributions b and c of the developer amount per unit area carried on the carrier and the distributions d and e of magnetic particle per unit length in the longitudinal direction of the developer carrier in the rotation direction of the developer carrier are shown. FIG. FIG. 7
In the above, Wz represents the width of the developer accommodating portion, Lm represents the length in the longitudinal direction of the magnet roller, and Wd represents the width in which the developer can exist in the developing device due to the side seal.

In order to make the magnetic force carrying force of the developer carried by the developer carrying body uniform, it is desirable that the magnetic force distribution in the longitudinal direction of the developer carrying body be uniform. However, in the conventional developer carrier, as shown by a symbol a in the figure, the magnetic force distribution of the magnetic roller as the magnetic field generating means extending inside the carrier by the length Lm in the longitudinal direction is at the center. While the magnetic field is almost uniform in the part and its vicinity, the magnetic field is strong at both ends and therefore the magnetic force is slightly strong. For this reason, the magnetic particle carrying capacity is increased at the end of the magnet roller, and the magnetic particles on the developer carrying member move to both ends of the developer carrying member having a strong magnetic force each time when passing through the developing area. Regarding this, if the length Lm of the magnet roller is made sufficiently long so that the formed image width falls within the range near the central portion where the magnetic force distribution of the magnet roller is uniform, the entire image width is obtained. A uniform magnetic force bearing force can be obtained. However, in the case of such a configuration, since the apparatus becomes large-sized, the portions where the magnetic force of both end portions of the magnet roller has conventionally become strong do not enter the image width or approach both end portions of the image width. It was configured to end up.

For this reason, as indicated by the symbol d in the figure, the magnetic particles uniformly carried over the entire area of the developer carrying member are gradually moved to the one having a strong magnetic force while being transported, and the code is given. As indicated by e, the developer carrying member is biased toward both ends h. As a result, the amount of magnetic particles carried per unit length of the developer carrying member in the developer carrying direction is reduced in the part 1 near the both ends adjacent to the center of the both ends.

In the developing device having the toner concentration self-controlling mechanism as shown in the above-mentioned Japanese Patent Laid-Open No. 63-225266, when the carrying amount of the magnetic particles decreases in the area 1 near both ends of the developer carrying member, In this portion, the amount of toner taken into the developer in the immovable layer increases due to the above-described principle of toner concentration self-control. Further, also in the developing device as shown in Japanese Patent Application No. 7-119340, the amount of toner taken into the developer accumulating portion becomes large in the portions 1 near both ends on the developer carrying member. Therefore, in any case, when the above-described toner concentration self-control is performed, the toner concentration increases near both ends of the image.

FIG. 8 is a block diagram showing the arrangement of a developer carrier and a developer regulating member that have been proposed in the past. As shown in the figure, the developer passing through the gap between the surface of the developer carrier 21 and the developer regulating member 22 provided at a predetermined distance from the surface of the developer carrier 21 is
The width Wd that can exist in the developing device is regulated by a side seal (not shown) arranged on the upstream side in the developer conveying direction. Further, this developer is, as indicated by the symbol b in FIG.
The developer regulating member 22 regulates the amount of the developer per unit area on the developer carrier substantially uniformly from the surface of the developer carrier to a thickness of 0.04 g / c〓. When the developer passes through the gap between the developer control member 22 and the developer carrying member 21, immediately after that, the developer tends to spread to both sides of the width Wd, as indicated by reference sign c in FIG. 7. . For this reason, the amount of magnetic particles per unit width carried near the widthwise ends of the developer carrying member tends to decrease. The amount of magnetic particles in the portion where the amount of the developer carrier is reduced is affected by the magnetic force of the magnet roller inside the developer carrier described above, and the developer carrier end portion (see FIG. 7).
(Indicated by symbol h in FIG. 7), the amount of magnetic particles carried in the vicinity of the end portion (indicated by symbol l in FIG. 7) adjacent to the center side is further reduced. Therefore, due to the above-described principle of toner concentration self-control, the toner concentration becomes high in the vicinity of both ends of the developer carrying member.

In this way, the developer whose both ends of the magnet roller have a strong magnetic force and whose width Wd that can exist in the developing device is regulated by the side seals serves as the developer regulating member. When the toner passes through the gap with the developer carrying member, it immediately spreads to both sides immediately thereafter, so that the toner concentration tends to increase in the vicinity of both ends of the developer carrying member. In addition to this, generally, in the vicinity of the end portion of the formed image, the ratio of forming an image is remarkably lower than in the central portion side, and the toner consumption amount is small, so that the toner concentration is likely to increase only in this portion.

In order to prevent the developer layer on the surface of the developer carrier from being biased to one side or partly falling off when the entire developing device having the toner concentration self-control mechanism is tilted, A developing device configured so that the developer in the developer accommodating portion is packed with the surface of the developer carrier to keep the toner concentration of the developer layer on the surface of the developer carrier constant in the longitudinal direction of the developer carrier. Has also been proposed (for example, JP-A-64-105975). However, in this developing device, since the developer is carried by the magnetic force, the magnetic field generating means provided in the developer carrier and extending in the longitudinal direction has a strong magnetic force at both ends as compared with the central part side. That the width that can exist in the developing device is regulated by the side seals, and when the developer passes through the gap between the developer regulating member and the developer carrying member, it spreads to both sides immediately after that. The toner concentration tends to be high near both ends of the agent carrier, and no consideration is given to suppressing the increase in toner concentration that occurs near both ends in the longitudinal direction of the developer transport member as described above.

Further, Japanese Patent Application No. 7-349820 discloses that the amount of toner that can be taken into the developer accommodating portion is smaller at both end portions in the longitudinal direction of the developer carrying member than at the central portion. There has been proposed a developing device provided with an intake amount regulating means. However, since the amount of taken-in toner depends on the mechanical accuracy of the parts constituting the toner-taken-in amount controlling means, the amount of taken-in toner varies due to individual differences in the devices. Further, if the accuracy is increased, there is a problem that the yield is reduced and the cost is inevitably increased.

The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus equipped with a developing device having a toner concentration self-control mechanism,
An image forming apparatus that suppresses an increase in toner concentration near the edge of the developer carrying member, and does not cause toner scattering, contamination inside the apparatus, and scumming of a formed image due to an increase in toner concentration near the edge of the developer carrying body. To provide.

[0016]

In order to achieve the above object, the invention of claim 1 is a two-component developer containing a toner and magnetic particles on a developer carrier having magnetic field generating means inside. The amount of the developer carried on the developer carrying member is regulated by magnetically carrying the developer in the developer accommodating portion in which the developer is stored and passing through the gap with the developer regulating member, and then the latent image is formed by the rotation. A toner accommodating portion that conveys the developer to the developing area facing the carrier, communicates with the developer accommodating portion through the toner intake opening, and is stored so as to contact the developer in the developer accommodating portion. In the developing step of taking in the toner of No. 1 by the movement of the developer, a step of forming a latent image in which a large amount of toner adheres to the end portion in the longitudinal direction of the latent image carrier at the time of non-image formation; With the developer carrier It is characterized in that provided a step of visual image of.

According to a second aspect of the present invention, the developer in the developer accommodating portion, in which the two-component developer containing toner and magnetic particles is stored, is magnetically carried on the developer carrying body having the magnetic field generating means inside. Then, after the amount of the developer carried on the developer carrying member is restricted by passing through the gap with the developer restricting member, the developer is conveyed by rotation to the developing area facing the latent image carrying member. A developing device that is in communication with the developer accommodating portion through the toner accommodating opening and that captures toner stored in the toner accommodating portion so as to contact the developer in the developer accommodating portion by moving the developer. In the image forming apparatus, a latent image is formed on the end portion in the longitudinal direction of the latent image carrier so that a large amount of toner adheres when the image is not formed, and the latent image is visualized by the developer carrier. Is also characterized by It is. Here, as a latent image to which a large amount of the toner is attached, when a visible image is formed,
At the end of the latent image carrier in the longitudinal direction, it is possible to use a latent image in which the entire visible region of the predetermined region becomes a solid black image.

According to a third aspect of the present invention, in the second aspect of the present invention, the latent image on which a large amount of the toner adheres is gradually transferred toward both ends in the longitudinal direction of the latent image carrier. The feature is that the latent image has a large amount of adhesion. Here, as a latent image in which a large amount of toner gradually adheres to both ends of the latent image carrier in the longitudinal direction, when the latent image carrier is visualized, the ends of the latent image carrier in the longitudinal direction are formed. In the section, a latent image in which a gray image gradually becomes a black solid image can be used from one end to the other end of a predetermined visible image area.

The invention of claim 4 is the same as claim 2 or 3.
In the invention, the formation of the latent image in which a large amount of the toner adheres and the visualization thereof are performed before or after the image formation.

According to a fifth aspect of the present invention, in the second, third or fourth aspect of the invention, the latent image on which a large amount of the toner adheres is removed from the charging potential of the non-image area on the latent image carrier. It is characterized in that it is formed by using an eraser. Here, when the latent image is formed by using the eraser, the developing method is a normal developing method in which the toner is attached to the area where the charging potential remains, or the toner is attached in the area where the charging potential is removed. Either method of reversal development may be used.

According to the first to fifth aspects of the present invention, during non-image formation, a latent image is formed such that a large amount of toner adheres to the longitudinal end of the latent image carrier, and the latent image is formed on the developer carrier. When the image is visualized by, the toner is rapidly consumed at the end portion in the longitudinal direction of the developer carrying member, so that the bulk density of the toner in that portion decreases. Then, the magnetic particles in the adjacent portions having a high bulk density move to the portions having a low bulk density, so that the toner concentration distribution at the longitudinal end portions on the developer carrying member becomes substantially uniform. This will be described with reference to FIG. In the figure, reference numeral 1 indicates a portion containing a small amount of magnetic particles and a large amount of toner, and reference numeral h indicates a portion containing a large amount of carriers and a small amount of toner. In FIG. 7, a latent image is formed on the end of the latent image carrier in the longitudinal direction such that a large amount of toner adheres to the portion indicated by reference numeral l in the figure, and when a visible image is formed, The bulk density of the toner is reduced. Then, the carrier in the high bulk density portion (h) of the adjacent carriers moves to the low bulk density portion l, so that the toner concentration distribution at the end portion in the longitudinal direction on the developer carrier becomes substantially uniform. Become.

In particular, according to the third aspect of the invention, since a latent image in which a large amount of toner adheres gradually is formed in the longitudinal direction of the developer carrying member, toner bulk consumption becomes low due to toner consumption. The step between the portion and the other portion is gentle. Therefore, the distribution of the developer when the carrier in the high bulk density portion moves to the low bulk density portion becomes smooth with few steps.

Particularly, in the invention of claim 4, the formation of a latent image in which a large amount of toner adheres and the visualization thereof are
Since it is executed before or after the image formation, it is not necessary to provide a dedicated detection timing means or the like in order to form a latent image in which a large amount of toner adheres.

Further, particularly in the invention of claim 5,
Since a latent image with a large amount of toner is formed by the eraser that removes the charging potential of the non-image area of the latent image carrier, a dedicated image input for forming a latent image with a large amount of toner is attached. There is no need to prepare a device or an image pattern. When developing a latent image with a large amount of toner adhered by a regular developing method, a predetermined area on the surface of the latent image carrier is charged by a charging device and then a latent image with a large amount of toner adhered by an eraser. Erase the area other than the range. As a result, the charging potential remains in the latent image range,
Since the charging potential is removed in the other area, when the charged area passes through the developer carrying member, only the area of the latent image is visualized by the developer. (Hereinafter, margin)

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter, referred to as a copying machine) as an image forming apparatus will be described below. In the following description, parenthesized reference numerals indicate reference numerals in other drawings. FIG.
1 is a schematic configuration diagram of a copying machine according to the present embodiment. Around the photosensitive drum 11 as a latent image carrier, a charging device 12, an eraser 13, an exposure device 1 along the drum rotation direction.
4, developing device 15, transfer device 16, cleaning device 1
7 are arranged. In FIG. 2, other peripheral devices are omitted.

The photoconductor drum 11 is rotationally driven in the direction of the arrow at a constant speed during copying by a driving means such as a motor (not shown). After being uniformly charged in the dark by the charging device 12, the eraser 13 removes the charging potential in the non-image area. Then, the exposure device 14 irradiates and forms a light image of the document, and the electrostatic latent image is carried on the outer peripheral surface of the photosensitive drum 11. Then, the electrostatic latent image is developed (visualized) by a developer supplied from a developing sleeve 4 described later while passing through the developing device 15. The development by the developing sleeve 4 is performed by applying a developing bias voltage to the developing sleeve 4 from a power source (not shown). The toner image developed into the electrostatic latent image is transferred to the transfer device 1
At 6, the transfer sheet P is transferred to the transfer sheet P conveyed by the transfer sheet conveying member 18. The transfer in the transfer device 16 is performed by applying a bias voltage having a polarity opposite to the charge of the toner image on the photosensitive drum 11 from the surface of the transfer paper P opposite to the surface facing the photosensitive drum 11. The transfer paper P on which the toner image has been transferred is output to a discharge tray (not shown) through a fixing process such as heat fusion and pressure fixing. The transfer paper P is transferred by the transfer paper transport member 18 to the photosensitive drum 11
Paper is fed at the timing when the leading edge of the upper toner image reaches the paper transfer position. Further, the untransferred toner remaining on the photoconductor drum 11 after the toner image transfer is removed from the photoconductor drum 11 by the cleaning device 17, and is collected in the cleaning device 17. After that, the surface of the photoconductor drum 11 is subjected to removal of residual charges by a charge eliminating device (not shown). Then, it is charged again by the charging device 12, and thereafter, the same image forming process is repeated for the required number of copies.

FIG. 3 is a partial cross-sectional view showing a schematic structure of the developing device 15 applied to the copying machine. The developing device 15 is provided on the side of a cylindrical photosensitive drum 11 which is a latent image carrier, and has a support case 2 having an opening 1 formed toward the photosensitive drum 11, and the opening 1 A part of the developing sleeve 4 is exposed, and a developing sleeve 4 as a developer carrying member carrying a developer 3 composed of toner and magnetic particles (hereinafter, referred to as carrier) on its surface, and carried and carried on the developing sleeve 4. It is composed of a doctor 5 as a developer regulating member for regulating the amount of the developer 3, a developer accommodating member 6 forming a space for accommodating the developer staying above the developing sleeve 4, and a toner hopper 7 as a toner accommodating portion. Has been done.

The developing sleeve 4 of the above-mentioned agent accommodating member 6
The end portion 6a on the upstream side in the rotation direction of the roller extends along the developing sleeve 4 with a predetermined distance from the developing sleeve 4, and faces the photosensitive drum 11 with the developing sleeve 4. A developer accommodating portion A for accommodating the developer that has not been supplied to the developing position of the portion and is prevented from proceeding by the agent accommodating member 6 is formed. Inside the developing sleeve 4 facing the developer accommodating portion A, a magnetic pole of a magnet roller (not shown) as magnetic field generating means is arranged. Further, the toner hopper 7 is
A toner replenishing opening 7 that is adjacent to the upstream side of the developer accommodating portion A in the developer conveying direction and faces the surface of the developing sleeve 4.
A toner agitator 8 as a toner sending member for sending the toner 9 to the toner supply opening 7a while stirring is provided in a space adjacent to the toner supply opening 7a.

In the developing device 15 having the above-described structure, the developer 3 on the developing sleeve 4 is conveyed as the sleeve 4 rotates in the direction of the arrow, and is regulated by the agent accommodating member 6 to form a thin layer. The thinned developer 3 is conveyed to a developing area facing the photoconductor drum 11 rotating in the arrow direction. Then, in the developing area, toner is supplied to the electrostatic latent image formed on the photosensitive drum 11, and the electrostatic latent image is visualized. The developer 3 that has not been used for visualization is conveyed along with the rotation of the developing sleeve 4, and after taking in the new toner 9 supplied from the toner agitator 8 and supplied from the toner replenishment opening 7a,
Return to the developer container A.

Here, in the toner agitator 8, one end of a plate-shaped blade portion 8a as a feeding member is attached along the longitudinal direction of a rotary shaft 8b which is rotationally driven in the arrow direction by a driving means (not shown). When the rotating shaft 8b rotates in the direction of the arrow, the toner 9 is sent toward the toner replenishing opening 7a while stirring the toner 9 in the toner hopper 7 on the surface of the blade portion 8a on the upstream side in the rotating direction. Therefore,
The longer the distance from the center of rotation of the rotating shaft 8b to the tip of the blade 8a, the higher the ability to stir the toner 9,
Further, the toner can be efficiently sent to the developer accommodating portion A. The internal pressure of the developer 3 containing the new toner in the toner hopper 7 increases due to the regulation of the agent accommodating member 6, so that the toner of the developer 3 is dispersed and the toner is charged. As described above, since the toner in the developer 3 on the developing sleeve 4 can be charged by the increase in the internal pressure of the developer in the developer accommodating portion A, the developer 3 such as a paddle or a screw can be charged or stirred. No complicated stirring mechanism is required.

On the other hand, a part of the developer 3 which is not supplied to the developing area and is prevented from advancing by the agent accommodating member 6 is stored in the developer accommodating portion A by the internal pressure and gravity of the developer 3 itself and is absorbed by the toner hopper 7. It moves toward the toner supply opening 7a.
The developer 3 that has moved to the vicinity of the toner supply opening 7a
Is conveyed so as to circulate to the agent containing member 6 side as the developing sleeve 4 rotates.

The execution of the image forming process and the paper feeding process in the copying machine are controlled by a control unit (not shown). This control unit includes a CPU (Central Processing Unit), R
It is composed of an OM, a RAM, an I / O controller, and the like. Of these, the CPU controls the operation of the entire copying machine and, as will be described later, in order to prevent the toner concentration from increasing near the both ends of the developing sleeve 4, the CPU is provided at both ends in the longitudinal direction of the photosensitive drum 11. A process of forming a latent image in which a large amount of toner adheres and converting the latent image into a visible image is executed.

Next, a description will be given of an embodiment in which a latent image in which a large amount of toner adheres is formed on both ends of the photosensitive drum 11 in order to prevent the toner concentration from increasing near the both ends of the developing sleeve 4. FIG. 1 is a schematic perspective view of FIG. 2, showing the arrangement of the photosensitive drum 11 and its peripheral devices. However, the eraser 13 and the exposure apparatus 1 shown in FIG.
4, the supporting case 2 of the developing device 15 and the toner hopper 7.
Are omitted.

In this copying machine, when the image forming process for one job is completed (or before it is started), a latent image is formed so that a large amount of toner adheres to both ends of the photosensitive drum 11 in the longitudinal direction. The latent image is made visible by the developing sleeve 4. In FIG. 1, as a latent image to which a large amount of toner adheres, a latent image that becomes a solid black image by development is formed on both ends of the photosensitive drum 11 in the longitudinal direction, and the latent image passes through the developing sleeve 4. Sometimes it shows the state when it is visualized. By visualizing,
Solid black images A are formed on both ends of the photosensitive drum 11 in the longitudinal direction.

As described above, when the latent image formed on both ends of the photosensitive drum 11 in the longitudinal direction passes through the developing device (15) and is visualized by the developer carried by the developing sleeve 4, Since the toner is rapidly consumed at both ends in the longitudinal direction of the developing sleeve 4, the bulk density of the toner in that portion is lowered, and the carrier in the adjacent portion having a high bulk density moves to the portion having a low bulk density. Therefore, the toner concentration distribution at both ends of the developing sleeve 4 in the longitudinal direction becomes substantially uniform.

According to the copying machine configured as described above,
Timing other than the normal image forming process, that is, 1
Before or after the image forming process of the job, by forming a latent image in which a large amount of toner adheres to both end portions of the photosensitive drum 11 in the longitudinal direction, the toner concentration at the both end portions of the developing sleeve 4 in the longitudinal direction is increased. The distribution can be substantially uniform. Therefore, the toner concentration does not rise abnormally near both ends of the developing sleeve 4, and toner scattering, contamination inside the apparatus, and the formed image caused by the abnormal rise in toner concentration near the both ends of the developing sleeve 4 occur. It is possible to prevent scumming.

The timing for forming a latent image in which a large amount of toner adheres to both ends of the photosensitive drum 11 in the longitudinal direction is not limited to the start or end of the image forming process of one job. It may be executed at any timing other than the normal image forming process.
In addition, the formation of a latent image in which a large amount of toner adheres is shown in FIG.
A publicly known method such as the exposure device 14 shown in FIG. 1 may be used, or a dedicated exposure device for forming a latent image with a large amount of toner attached may be installed. When the exposure device 14 forms a latent image on which a large amount of toner adheres, an image pattern for a latent image on which a large amount of toner adheres is prepared.

In the copying machine of this embodiment, a latent image on which a large amount of toner adheres is formed by using the eraser 13 shown in FIG. Further, in this embodiment, the regular development method is used for developing the electrostatic latent image. In this regular development method, a predetermined area on the surface of the photosensitive drum 11 is charged by the charging device 12, and then the area other than the area of the latent image where a large amount of toner adheres is erased by the eraser 13. Then, since the charged potential remains in the area of the latent image and the charged potential is removed in the other areas, when the charged area passes through the developing device 15, the latent image is formed by the developer carried by the developing sleeve 4. Only the range of will be visualized. As described above, by using the eraser 13, it is necessary to provide a dedicated exposure device for forming a latent image in which a large amount of toner adheres, or prepare an image pattern for a latent image in which a large amount of toner adheres. Is eliminated, the device is downsized,
Cost reduction can be achieved. The electrostatic latent image may be developed by a so-called reversal development method, in which toner is attached to the area where the charging potential is removed.

The transfer paper P is not fed at the time of forming a latent image in which a large amount of toner adheres to form a visible image. For this reason, in the contact transfer method using a transfer member such as a transfer roller or a transfer belt, the visible solid black image may cause background stain on the surface of the transfer member. In this case, the toner adhering to the transfer member is scraped off by a blade or the like, or the transfer member is temporarily separated from the photosensitive drum 11. A bias voltage opposite to the normal transfer bias may be applied to the transfer member to prevent transfer to the transfer member side.

Next, as another embodiment, an embodiment will be described in which a latent image is formed such that a large amount of toner gradually adheres to both ends of the photosensitive drum 11 in the longitudinal direction. FIG. 4 is a schematic perspective view of FIG. 2, and shows the arrangement of the photosensitive drum 11 and its peripheral devices similarly to FIG. In the copying machine of this embodiment, when the image forming process for one job is completed (or before it is started), a latent image in which a large amount of toner gradually adheres to both ends of the photosensitive drum 11 in the longitudinal direction is formed. An image is formed, and the latent image is visualized by the developing sleeve 4. That is, as shown in FIG. 4, as a latent image in which a large amount of toner gradually adheres to both ends of the photosensitive drum 11 in the longitudinal direction, a latent image that becomes a black solid image by development and the black solid image are formed. The photosensitive drum 1 at a position adjacent to the latent image
A latent image that becomes a gray image is formed in the longitudinal direction of the image 1 toward the center, and these two types of latent images are visualized by the developing sleeve 4. Here, the gray image is an image of a color such that the image density becomes approximately halfway between black and white (halftone) when visualized. In FIG. 4, a latent image that becomes a solid black image by development and a latent image that becomes a gray image by development are formed on both ends of the photosensitive drum 11 in the longitudinal direction, and these latent images pass through the developing sleeve 4. Sometimes it shows the state when it is visualized. By the visualization, a black solid image A and a gray image B are formed on both ends of the photosensitive drum 11 in the longitudinal direction.

As described above, when each latent image formed on both ends of the photosensitive drum 11 in the longitudinal direction passes through the developing device (15) and is visualized by the developer carried by the developing sleeve 4. By the same action as in the case of the above-described embodiment, the carrier in a portion having a high bulk density in a portion adjacent to both ends in the longitudinal direction of the developing sleeve 4 moves to a portion having a low bulk density. The toner concentration distribution at both ends in the longitudinal direction becomes substantially uniform. In particular, in this embodiment, since a latent image that becomes a gray image is formed adjacent to a latent image that becomes a black solid image, toner consumption is changed from a latent image that becomes a black solid image to a latent image that becomes a gray image. Gradually decrease toward the end. Therefore, at both ends in the longitudinal direction of the developing sleeve 4, the toner density gradually decreases from the black solid image portion to the gray image portion.

According to the copying machine configured as described above,
Timing other than the normal image forming process, that is, 1
Before or after the image forming process of the job, as a latent image in which a large amount of toner gradually adheres toward both ends in the longitudinal direction of the photoconductor drum 11, a latent image forming a solid black image and a latent image forming a gray image are formed. By forming the image, the toner density distribution at both ends in the longitudinal direction of the developing sleeve 4 can be made substantially uniform. Particularly, in the portion where the latent image that becomes a gray image is visualized, the bulk density of the toner is less reduced than in the portion where the latent image that becomes a black solid image is made visible. In the toner, the bulk density of the toner gradually decreases toward the ends, and along with this, the carrier in the adjacent portion having a high bulk density also gradually increases toward both ends. According to this, since the level difference between the portion where the toner concentration is low and the portion where the toner concentration is not is gentle in the vicinity of both ends in the longitudinal direction, the carrier in the adjacent portion having a high bulk density has a low bulk density. The distribution of the developer when it moves to the part also becomes smooth with few steps. Therefore, as compared with the case where only the latent image that becomes a black solid image is formed on both ends of the photoconductor drum 11 in the longitudinal direction, the toner density distribution is made more uniform at both ends of the developing sleeve 4 in the longitudinal direction. be able to. In this case as well, the toner concentration does not rise abnormally near the ends of the developing sleeve 4, and the toner scatters due to the abnormal rise in the toner concentration near the ends of the developing sleeve 4, contamination inside the apparatus, and formation. It is possible to prevent the background stain of the image.

In the copying machine of the above-described embodiment, the latent image which becomes a black solid image is formed by using the eraser 13, but it is difficult to form the gray image latent image by the eraser 13. Alternatively, image patterns for a black solid image and a gray image may be prepared in advance and a latent image may be formed by the exposure device (14).

Further, in FIG. 4, a latent image in which the entire surface becomes a gray image is formed adjacent to the latent image in which the entire surface becomes a black solid image. May be changed stepwise or steplessly, or the shade may be changed stepwise or steplessly from the gray image B to the white part. When the lightness is changed stepwise or stepless in this way, the distribution of the developer in the longitudinal direction of the developing sleeve 4 can be made smoother.

Further, the shapes of the black solid image and the gray image are not limited to the quadrangle, and other shapes may be formed. Also,
Instead of an image of uniform density in which the entire surface is black or gray, a plurality of fixed or unspecified patterns may be combined.
That is, the shape, density, and the like of the image are not particularly limited as long as it is an image in which the toner consumption is large at the end portion in the longitudinal direction of the developing sleeve 4.

Next, the operation of the copying machine when executing the image forming process in the above-mentioned embodiment will be described with reference to the flowchart of FIG. 5 while referring to FIGS. Here, a case will be described in which only a latent image that becomes a solid black image is formed as shown in FIG. First, when a copy start is accepted from an operation panel (not shown) (step 10
1) Start the image forming process (step 10)
2). In this image forming process, the surface of the photosensitive drum 11 is uniformly charged by the charging device 12, the paper size of the transfer paper P is detected by an optical system (not shown), and the eraser 13 removes the charging potential of the non-image area. After that, an electrostatic latent image is formed on the photosensitive drum 11 by the exposure device 14,
Development is performed by the developing device 15. Then, the transfer device 16 transfers the toner image onto the transfer paper P, and then the cleaning device 17 removes the untransferred toner on the photosensitive drum 11. This series of image forming processes is repeated until the copying of one job is completed (step 103), and when the copying of one job is completed (Y in step 103).
es), and then, the operation proceeds to the operation of forming a latent image that becomes a black solid image. First, the charging device 12 charges a predetermined area on the surface of the photoconductor drum 11 (step 104), and the eraser 13 erases an area other than the area of the latent image forming a black solid image (step 105). Next, a developing bias voltage is applied to the developing sleeve 4 of the developing device 15 to visualize the latent image which is a black solid image formed on the photosensitive drum 11 (step 106). After that, the black solid image is cleaned by the cleaning device 17 (step 107).

The latent image forming a solid black image may be formed immediately after the image forming process of one job is completed as described above, or immediately before the image forming process of one job is started. You may do it. Alternatively, the process may be executed after the image forming process of one job is completed and a predetermined time has elapsed, or after a predetermined instruction is input. The latent image forming a solid black image can be formed in the middle of one job. However, the latent image forming operation for forming a solid black image is performed in order to eliminate background stains on all the formed images of one job. It is desirable to execute before or after one job. Further, by setting the timing in advance so that the latent image forming the black solid image is executed before or after one job, a dedicated detection for detecting the timing forming the latent image forming the black solid image. Since it is not necessary to provide timing means or the like, it is possible to reduce the size and cost of the device. (Hereinafter, margin)

By the way, since the number of copies of one job may be one or may be more than one, depending on the number of copies of one job, the latent image forming a black solid image may not be executed for a long time. is there. However, there is almost no problem with the number of copies to be executed in one general job. FIG. 6 shows the relationship between the number of copies and the toner density at the end of the developing sleeve 4.
In the figure, x indicates the number of copies until the toner density is reached at which toner scattering occurs. The number of copies is x
When the toner density exceeds x'and the toner density exceeds x '(the area exceeding the broken line), toner scattering or the like starts to occur. However, since the value of this x is usually several thousand sheets, a general copy number range of one job ( ~ Dozens of sheets) does not cause any particular problem. Incidentally, in an experiment in which a chart having an image area of 6% was continuously copied, toner scattering and the like occurred around 1500 sheets. However, the operation of forming a latent image that becomes a black solid image is
If necessary, it may be executed in the middle of the image forming process of one job.

[0049]

According to the first to fifth aspects of the present invention, the latent image is formed so that a large amount of toner adheres to the developer carrying member at the longitudinal end of the developer carrying member. Since a large amount of toner is consumed at the end portion in the longitudinal direction of the toner, even if the toner concentration rises at the end portion of the developer carrying member, the toner concentration distribution at the end portion in the longitudinal direction on the developer carrying member is increased. Can be substantially uniform. Therefore, an increase in toner concentration near the edge of the developer carrying member is suppressed, and toner scattering, contamination inside the apparatus, and scumming of the formed image caused by an increase in toner concentration near the edge of the developer carrying member are prevented. be able to.

In particular, according to the third aspect of the invention, since the latent image is formed such that a large amount of toner gradually adheres in the longitudinal direction of the developer carrier, the longitudinal direction of the developer carrier is increased. The distribution of the developer at the edges of the toner is also smooth with few steps, and the toner concentration distribution can be made more uniform.

In particular, according to the invention of claim 4, the latent image is formed so that a large amount of toner adheres and the visible image is formed before or after the image formation. Therefore, a large amount of toner adheres. When forming such a latent image, it is not necessary to provide a dedicated detection timing means or the like, and the size and cost of the apparatus can be reduced.

According to the fifth aspect of the invention, the latent image on which a large amount of toner adheres is formed by the eraser for removing the charging potential of the non-image area of the latent image carrier. It is not necessary to prepare a dedicated image input device or an image pattern for forming a latent image in which a large amount of toner adheres, so that the device can be downsized and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of a copying machine according to an embodiment.

FIG. 2 is a schematic configuration diagram of a copying machine according to the embodiment.

FIG. 3 is a partial cross-sectional view showing a schematic configuration of a developing device.

FIG. 4 is a schematic perspective view of another copying machine according to the embodiment.

FIG. 5 is a flowchart showing the operation of the copying machine when executing the image forming process.

FIG. 6 is an explanatory diagram showing the relationship between the number of copies and the toner density at the end of the developing sleeve.

FIG. 7 is an explanatory diagram of a magnetic force distribution in the longitudinal direction of the developer carrier, a developer amount distribution per unit area, and a magnetic particle amount distribution per unit length in the developer carrier rotating direction.

FIG. 8 is a configuration diagram showing an arrangement of a developer carrier and a developer regulating member that have been conventionally proposed.

[Explanation of symbols]

 4 Developing Sleeve 11 Photoreceptor Drum 12 Charging Device 13 Eraser 14 Exposure Device 15 Developing Device 16 Transfer Device 17 Cleaning Device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hajime Koyama 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd.

Claims (5)

[Claims] Claims: 1. A developer control unit, in which a developer in a developer accommodating portion in which a two-component developer containing toner and magnetic particles is stored is magnetically carried on a developer carrying member having a magnetic field generating means inside, thereby regulating the developer. After the amount of the developer carried on the developer carrying member is regulated by passing through the gap with the member, the developer is conveyed by rotation to the developing area facing the latent image carrying member and the toner intake opening portion is formed. In a developing process in which the toner in the toner storage portion, which is communicated with the developer storage portion via the, and is stored in contact with the developer in the developer storage portion, is taken in by the movement of the developer, at the time of non-image formation, The present invention is characterized in that a step of forming a latent image in which a large amount of toner adheres to an end portion in the longitudinal direction of the latent image carrier and a step of visualizing the latent image by the developer carrier are provided. Toner density control method . 2. A developer control unit, in which a developer in a developer accommodating portion, in which a two-component developer containing toner and magnetic particles is stored, is magnetically carried on a developer carrier having a magnetic field generating means therein. After the amount of the developer carried on the developer carrying member is regulated by passing through the gap with the member, the developer is conveyed by rotation to the developing area facing the latent image carrying member and the toner intake opening portion is formed. In an image forming apparatus including a developing device, which communicates with a developer containing portion via a developer and takes in the toner in the toner containing portion stored so as to contact the developer in the developer containing portion by the movement of the developer. In the non-image formation, a latent image is formed so that a large amount of toner adheres to an end portion in the longitudinal direction of the latent image carrier, and the latent image is visualized by the developer carrier. Image forming apparatus. 3. The image forming apparatus according to claim 2, wherein the latent image with a large amount of toner adheres to the latent image carrier such that the toner gradually adheres to both ends in the longitudinal direction of the latent image carrier. An image forming apparatus characterized by being an image. 4. The image forming apparatus according to claim 2 or 3, wherein formation of the latent image having a large amount of toner adhered thereto and visualization thereof are performed before or after image formation. Forming equipment. 5. The image forming apparatus according to claim 2, 3 or 4, wherein an eraser is used to remove a charge potential of a non-image area on the latent image carrier from the latent image to which a large amount of toner adheres. An image forming apparatus characterized by forming.